Clinical Approach to Cough

Comprehensive Practical Framework

1
Symptom Overview
Overview
2
Pathophysiology
Mechanism
3
History Taking
History
4
Physical Examination
Examination
5
Differential Diagnosis
Differential
6
Investigations
Workup
7
Clinical Decision-Making
Algorithm
8
Pearls and Pitfalls
Summary

1. Symptom Overview

Understanding the clinical significance and classification of cough

Cough is one of the most common symptoms prompting patients to seek medical attention, accounting for approximately 30 million physician visits annually in the United States alone. It represents roughly 8% of all outpatient encounters. Chronic cough affects an estimated 10-20% of adults worldwide and significantly impacts quality of life, causing sleep disturbance, social embarrassment, urinary incontinence, and even syncope in severe cases. Understanding the systematic approach to cough evaluation is essential for every clinician.

Definition

Cough is a sudden, forceful expulsion of air from the lungs through the mouth. It is a complex protective reflex mechanism involving coordinated activation of respiratory muscles following stimulation of sensory receptors in the airways and other sites. While primarily a defense mechanism to clear the airways of secretions, foreign particles, and irritants, cough becomes pathological when it is excessive, persistent, or associated with underlying disease.

Classification by Duration

Duration is the single most important factor in narrowing the differential diagnosis of cough. The classification below guides the initial approach and determines the likelihood of various etiologies.

Category	Duration	Common Causes	Clinical Significance
Acute	Less than 3 weeks	Viral upper respiratory tract infection, acute bronchitis, pneumonia, COVID-19, influenza, pertussis (early), acute exacerbation of chronic obstructive pulmonary disease or asthma	Most commonly infectious; usually self-limiting; focus on excluding serious causes (pneumonia, pulmonary embolism, heart failure)
Subacute	3 to 8 weeks	Post-infectious cough, pertussis, unrecognized asthma, bacterial sinusitis, slowly resolving pneumonia	Often post-infectious; pertussis (“100-day cough”) is frequently missed; consider chest radiograph if not improving
Chronic	Greater than 8 weeks	Upper airway cough syndrome, asthma, gastroesophageal reflux disease, non-asthmatic eosinophilic bronchitis, angiotensin-converting enzyme inhibitor-induced cough, chronic bronchitis, bronchiectasis, lung cancer	Requires systematic evaluation; “The Big Three” account for more than 90% in non-smokers with normal chest radiograph

Classification by Character

Productive (Wet) Cough

Characterized by sputum production. The appearance of sputum provides diagnostic clues:

Clear/mucoid: Viral infection, asthma, chronic bronchitis
Yellow/green (purulent): Bacterial infection, though color alone is unreliable
Rust-colored: Pneumococcal pneumonia
Pink and frothy: Pulmonary edema
Blood-streaked: Bronchitis, bronchiectasis, tuberculosis, malignancy
Foul-smelling: Lung abscess, anaerobic infection

Non-Productive (Dry) Cough

No significant sputum production. Common causes include:

Upper airway cough syndrome: Post-nasal drip irritating pharyngeal receptors
Asthma (cough-variant): Cough may be the sole manifestation
Gastroesophageal reflux disease: Silent reflux without heartburn in up to 75%
Angiotensin-converting enzyme inhibitors: Affects 5-20% of patients
Interstitial lung disease: Progressive dry cough with exertion
Viral infections: Early phase before secretions develop

Sputum Characteristics and Clinical Correlations

Sputum Appearance	Volume	Associated Conditions
Clear, thin	Minimal to moderate	Viral infection, early asthma, allergic rhinitis
Thick, tenacious	Variable	Asthma, dehydration, chronic bronchitis
Purulent (yellow/green)	Moderate to copious	Bacterial bronchitis, pneumonia, bronchiectasis
Copious and purulent	Greater than 25 mL/day	Bronchiectasis, lung abscess, cystic fibrosis
Blood-tinged (hemoptysis)	Variable	Bronchitis, tuberculosis, malignancy, pulmonary embolism

Classification by Pattern and Timing

Pattern	Description	Suggests
Nocturnal cough	Worse at night, especially when lying flat	Asthma, gastroesophageal reflux disease, heart failure, upper airway cough syndrome
Early morning cough	Upon awakening, often productive	Chronic bronchitis, bronchiectasis (postural drainage of overnight secretions)
Post-prandial cough	Within 1-2 hours after meals	Gastroesophageal reflux disease, aspiration
Exercise-induced cough	Triggered by physical activity, cold air	Exercise-induced bronchoconstriction, asthma
Seasonal pattern	Predictable worsening during specific seasons	Allergic rhinitis, pollen-triggered asthma
Paroxysmal cough	Sudden, violent bouts of coughing, often with inspiratory “whoop”	Pertussis, foreign body aspiration
Barking cough	Harsh, seal-like quality	Croup (primarily pediatric), laryngeal pathology
Honking or brassy cough	Loud, bizarre quality; often absent during sleep	Habit cough, psychogenic cough (diagnosis of exclusion)

Key Concept: “The Big Three”

In immunocompetent, non-smoking adults with chronic cough and a normal chest radiograph, three conditions account for more than 90% of cases:

Upper Airway Cough Syndrome (formerly post-nasal drip syndrome) — approximately 20-40%
Asthma (including cough-variant asthma) — approximately 20-30%
Gastroesophageal Reflux Disease — approximately 10-40%

These conditions frequently coexist, and up to 25% of patients have more than one cause contributing to their cough. Successful treatment often requires addressing all contributing factors.

Impact on Quality of Life

Chronic cough significantly impairs quality of life and can lead to multiple complications:

Physical Complications

Urinary stress incontinence (especially in women)
Cough syncope (cough-induced fainting)
Rib fractures (particularly in osteoporotic patients)
Muscle strain and chest wall pain
Subconjunctival hemorrhage
Hernias (inguinal, umbilical)
Gastroesophageal reflux exacerbation

Psychosocial Impact

Sleep disturbance and fatigue
Social embarrassment and isolation
Work absenteeism and decreased productivity
Depression and anxiety
Fear of serious underlying disease
Relationship strain
Reduced exercise tolerance

2. Pathophysiology and Mechanisms

Understanding the underlying mechanisms of cough

Understanding the cough reflex arc is essential for comprehending how various conditions trigger cough and why certain treatments are effective. The cough reflex serves as a vital protective mechanism, clearing the airways of secretions, foreign material, and irritants. When this reflex becomes hypersensitive or chronically activated, it transitions from protective to pathological.

The Cough Reflex Arc

The cough reflex consists of five key components working in sequence:

Component	Structure	Function
Receptors	Sensory nerve endings in airways (larynx, carina, bronchi), pharynx, external auditory canal, esophagus, pericardium, diaphragm	Detect mechanical and chemical stimuli; highest density at larynx and carina (most sensitive areas)
Afferent Pathway	Vagus nerve (cranial nerve X) — primary pathway; also glossopharyngeal nerve (cranial nerve IX) and trigeminal nerve (cranial nerve V)	Transmit sensory information from peripheral receptors to the brainstem cough center
Integration Center	Cough center in the medulla oblongata (nucleus tractus solitarius); also influenced by higher cortical centers	Process afferent signals; coordinate efferent motor response; cortical influence allows voluntary suppression or initiation of cough
Efferent Pathway	Vagus nerve, phrenic nerve (diaphragm), spinal motor nerves (intercostal and abdominal muscles)	Carry motor commands to respiratory muscles to execute the cough maneuver
Effectors	Diaphragm, intercostal muscles, abdominal muscles, larynx (vocal cords), bronchial smooth muscle	Execute the three phases of cough: inspiratory, compressive, and expulsive phases

The Three Phases of Cough

1. Inspiratory Phase

Duration: Variable

Mechanism: Deep inspiration to approximately 50-90% of total lung capacity. The glottis remains open. Volume of inspired air determines force of subsequent cough.

Clinical note: Patients with restrictive lung disease or muscle weakness may have ineffective cough due to reduced inspiratory capacity.

2. Compressive Phase

Duration: Approximately 0.2 seconds

Mechanism: Glottis closes tightly. Expiratory muscles contract forcefully against the closed glottis, generating intrathoracic pressures up to 300 mmHg.

Clinical note: This phase is responsible for cough-related complications (syncope, rib fractures, hernias).

3. Expulsive Phase

Duration: 0.2-0.5 seconds

Mechanism: Glottis opens suddenly. Rapid expulsion of air at velocities up to 500 miles per hour. Dynamic airway compression enhances shearing forces to dislodge mucus and debris.

Clinical note: Airway collapse in chronic obstructive pulmonary disease reduces cough effectiveness.

Receptor Types and Clinical Relevance

Three main types of sensory receptors mediate the cough reflex, each with distinct characteristics and clinical implications:

Rapidly Adapting Receptors (RARs)

Location: Epithelium of larger airways (trachea, main bronchi)

Stimuli: Mechanical stimuli (touch, particulates), rapid changes in airflow, bronchospasm, edema

Fiber type: Myelinated Aδ fibers — fast conduction

Clinical relevance: Respond to foreign body aspiration, mucus, inhaled irritants. Responsible for immediate “defensive” cough.

C-Fiber Receptors

Location: Throughout airways and lung parenchyma (bronchial and pulmonary C-fibers)

Stimuli: Chemical irritants (capsaicin, bradykinin, prostaglandins), inflammatory mediators, acid

Fiber type: Unmyelinated C fibers — slow conduction

Clinical relevance: Mediate cough in asthma, gastroesophageal reflux disease, angiotensin-converting enzyme inhibitor-induced cough. Key target for cough hypersensitivity syndrome.

Slowly Adapting Receptors (SARs)

Location: Airway smooth muscle

Stimuli: Lung inflation, sustained stretch

Fiber type: Myelinated Aβ fibers

Clinical relevance: Primarily involved in breathing pattern regulation (Hering-Breuer reflex). May modulate cough threshold rather than directly triggering cough.

Anatomical Distribution of Cough Receptors

Location	Receptor Density	Afferent Nerve	Clinical Significance
Larynx	Very high	Superior laryngeal branch of vagus	Most sensitive area; aspiration protection; irritation causes violent cough
Carina	Very high	Vagus nerve	Critical defense zone; endotracheal tube positioning can trigger persistent cough
Trachea and main bronchi	High	Vagus nerve	Major airways well-protected; sputum clearance zone
Pharynx	Moderate	Glossopharyngeal nerve (cranial nerve IX)	Upper airway cough syndrome acts here; post-nasal drip irritation
External auditory canal	Low	Arnold’s nerve (auricular branch of vagus)	Arnold’s nerve reflex — ear examination or wax impaction triggers cough in 2-4% of people
Distal esophagus	Low	Vagal afferents	Gastroesophageal reflux disease may trigger cough via esophago-bronchial reflex without aspiration
Pericardium and diaphragm	Low	Phrenic and vagus nerves	Pericarditis, subphrenic abscess may present with cough

Often Overlooked Mechanism: Arnold’s Nerve Reflex

The external auditory canal contains sensory fibers from Arnold’s nerve (the auricular branch of the vagus nerve). In 2-4% of the population, stimulation of this nerve during ear examination, cerumen impaction, or even hearing aid use can trigger a cough reflex. Always examine the ears in patients with unexplained chronic cough — impacted cerumen may be a simple, treatable cause!

How Conditions Cause Cough

Understanding the specific mechanism by which each condition triggers cough guides targeted therapy:

Condition	Mechanism	Treatment Implication
Upper Airway Cough Syndrome (post-nasal drip)	Secretions drain posteriorly from nasal passages and sinuses, mechanically stimulating pharyngeal and laryngeal cough receptors. May also involve inflammatory mediators sensitizing receptors.	First-generation antihistamines (drying effect) plus decongestants; nasal corticosteroids for allergic component; treat underlying sinusitis if present
Asthma and Cough-Variant Asthma	Eosinophilic airway inflammation releases mediators that sensitize C-fiber receptors and rapidly adapting receptors. Bronchoconstriction stimulates mechanoreceptors. Cough may be only symptom without wheeze.	Inhaled corticosteroids to reduce inflammation; bronchodilators for symptom relief; response to therapy confirms diagnosis
Non-Asthmatic Eosinophilic Bronchitis	Eosinophilic inflammation of airways similar to asthma, but without bronchial hyperresponsiveness or airflow obstruction. Inflammatory mediators sensitize cough receptors.	Responds well to inhaled corticosteroids; does not respond to bronchodilators (distinguishes from asthma)
Gastroesophageal Reflux Disease	Two mechanisms: (1) Microaspiration of gastric contents irritates laryngeal and tracheobronchial receptors; (2) Esophago-bronchial vagal reflex — acid in distal esophagus triggers cough without aspiration. Up to 75% have “silent reflux” without heartburn.	Proton pump inhibitor twice daily for 2-3 months (acid suppression); lifestyle modifications; may require fundoplication in refractory cases
Angiotensin-Converting Enzyme (ACE) Inhibitor-Induced Cough	ACE inhibitors prevent breakdown of bradykinin and substance P, which accumulate in the airways and sensitize C-fiber receptors. Affects 5-20% of patients; more common in women and Asian populations.	Discontinue ACE inhibitor; switch to angiotensin receptor blocker (does not affect bradykinin metabolism); cough resolves in 1-4 weeks, occasionally up to 3 months
Chronic Bronchitis	Chronic inflammation leads to mucus gland hypertrophy and hypersecretion. Excess mucus mechanically stimulates rapidly adapting receptors. Defined as productive cough for at least 3 months in 2 consecutive years.	Smoking cessation is paramount; mucolytics may help; treat exacerbations; pulmonary rehabilitation
Bronchiectasis	Permanently dilated airways with impaired mucociliary clearance lead to chronic infection and inflammation. Copious sputum production stimulates mechanoreceptors; inflammatory mediators sensitize chemoreceptors.	Airway clearance techniques; treat underlying infection; long-term macrolides may reduce exacerbations
Interstitial Lung Disease	Fibrosis and distortion of lung architecture stimulate pulmonary C-fibers and stretch receptors. Inflammatory process releases mediators that sensitize cough receptors.	Treat underlying disease if possible; antifibrotic agents for idiopathic pulmonary fibrosis; cough often refractory and requires symptomatic management
Lung Cancer	Tumor directly irritates airway epithelium; may cause airway obstruction; post-obstructive pneumonia contributes. New or changed cough in smoker is red flag.	Treat underlying malignancy; palliative approaches for symptom control in advanced disease
Heart Failure	Pulmonary venous congestion stimulates pulmonary C-fibers (juxtacapillary or J receptors). Interstitial edema and airway edema contribute. Typically worse when supine.	Optimize heart failure management; diuretics reduce congestion; consider switching from ACE inhibitor if on one

Cough Hypersensitivity Syndrome

An Emerging Concept

Cough hypersensitivity syndrome describes a condition where the cough reflex becomes abnormally sensitive, resulting in coughing triggered by low-level stimuli that would not normally cause cough (such as talking, laughing, exposure to scents or temperature changes). Key features include:

Central sensitization: Heightened processing of cough signals in the brainstem and cortex
Peripheral sensitization: Upregulation and increased sensitivity of airway sensory nerves
Laryngeal paresthesia: Patients often describe throat tickle, irritation, or urge to cough
Allotussia: Cough triggered by non-tussive stimuli (talking, perfumes)
Hypertussia: Exaggerated cough response to known triggers

This concept helps explain why cough may persist despite treatment of identified causes and supports the use of neuromodulatory therapies (gabapentin, pregabalin, low-dose morphine) in refractory cases.

Pathophysiology of Cough Complications

The forceful nature of cough generates significant intrathoracic, intra-abdominal, and intracranial pressure changes that can lead to complications:

Complication	Mechanism	Risk Factors
Cough syncope	Increased intrathoracic pressure reduces venous return, leading to decreased cardiac output and cerebral perfusion. Similar mechanism to Valsalva maneuver.	Male sex, obesity, chronic obstructive pulmonary disease, severe paroxysmal cough
Stress urinary incontinence	Sudden increase in intra-abdominal pressure overcomes urethral sphincter resistance	Female sex, multiparity, pelvic floor weakness, obesity
Rib fractures	Repeated forceful contraction of intercostal and abdominal muscles creates stress on ribs	Osteoporosis, chronic corticosteroid use, metastatic bone disease, elderly patients
Subconjunctival hemorrhage	Elevated venous pressure transmitted to fragile conjunctival vessels	Anticoagulation, hypertension, severe paroxysmal coughing
Hernias	Repeated increases in intra-abdominal pressure stress weakened areas of the abdominal wall	Pre-existing fascial weakness, prior surgery, obesity, chronic cough

3. History Taking

A comprehensive approach to eliciting the cough history

Red Flags — Require Urgent Evaluation

The presence of any of the following warrants expedited investigation, often including chest imaging and specialist referral:

Hemoptysis — Malignancy, tuberculosis, pulmonary embolism, bronchiectasis
Unintentional weight loss (greater than 5% body weight) — Malignancy, tuberculosis, chronic infection
Night sweats — Tuberculosis, lymphoma, other malignancy
Fever persisting more than 1 week — Pneumonia, tuberculosis, abscess, empyema
Progressive dyspnea — Interstitial lung disease, malignancy, heart failure

Hoarseness lasting more than 3 weeks — Laryngeal cancer, recurrent laryngeal nerve involvement by lung cancer
Smoker over age 40 with new or changed cough — High risk for lung cancer
Stridor or significant dyspnea — Upper airway obstruction requiring urgent evaluation
Recurrent pneumonia in the same location — Endobronchial obstruction (tumor, foreign body)
Immunocompromised patient with new cough — Opportunistic infection, atypical pathogens

Systematic History: The “COUGHS” Approach

Use the mnemonic “COUGHS” to ensure comprehensive history taking for every patient presenting with cough:

C — Character and Course: What does the cough sound like (dry, wet, barking, whooping)? How has it evolved over time? Is it getting better, worse, or staying the same?
O — Output and Other Symptoms: Is there sputum production? What color, consistency, volume, and odor? Any hemoptysis? Associated symptoms: dyspnea, wheeze, chest pain, fever, rhinorrhea, heartburn, voice changes?
U — Understand Triggers and Timing: What makes it worse or better? Time of day (nocturnal, morning)? Relationship to meals, exercise, talking, position, environment, allergens, cold air?
G — General History: Past medical history (asthma, allergies, reflux, heart disease)? Current medications (especially angiotensin-converting enzyme inhibitors)? Smoking history (pack-years)? Occupational and environmental exposures?
H — How Does It Affect You?: Impact on sleep, work, social activities? Complications experienced (incontinence, syncope, chest pain)? Previous treatments tried and their effectiveness?
S — Sick Contacts and Special Circumstances: Recent illness in household or workplace? Travel history? Tuberculosis exposure? Immunocompromised state? Pets or animal exposures?

Duration-Specific History Questions

Duration	Key Questions to Ask	Rationale
Acute (less than 3 weeks)	“Did this start with cold symptoms?” “Any fever, body aches, sore throat?” “Have you been around anyone sick?” “Any chest pain or shortness of breath?”	Focus on infectious causes and excluding serious conditions (pneumonia, pulmonary embolism, heart failure)
Subacute (3-8 weeks)	“Did this follow a respiratory infection?” “Has anyone else had prolonged cough?” “Any whooping or vomiting with cough?” “Is it gradually improving?”	Post-infectious cough is most common; pertussis frequently missed; determine trajectory
Chronic (greater than 8 weeks)	“Do you take any blood pressure medications?” “Do you smoke or have you ever smoked?” “Any nasal congestion or post-nasal drip?” “Any heartburn or acid taste?” “Does exercise trigger it?”	Systematically evaluate “The Big Three” plus angiotensin-converting enzyme inhibitor use and smoking-related causes

Targeted Questions by Suspected Cause

Suspected Cause	Key Features	Ask This Question
Upper Airway Cough Syndrome (post-nasal drip)	Throat clearing, sensation of secretions in throat, nasal congestion, sneezing	“Do you feel mucus dripping down the back of your throat?” “Do you frequently need to clear your throat?” “Any nasal stuffiness or sneezing?”
Asthma / Cough-Variant Asthma	Episodic symptoms, known triggers, nocturnal symptoms, personal or family history of atopy	“Does cold air, exercise, or strong scents trigger your cough?” “Is it worse at night?” “Do you have allergies, eczema, or does asthma run in your family?”
Gastroesophageal Reflux Disease	Post-prandial symptoms, worse when lying down; note that up to 75% have no typical reflux symptoms	“Is your cough worse after eating or when lying flat?” “Any heartburn, acid taste, or regurgitation?” “Do you ever wake up coughing or choking?”
Angiotensin-Converting Enzyme Inhibitor-Induced Cough	Dry, tickling cough; onset days to months after starting medication	“Do you take any blood pressure medications? Can you name them?” “When did you start this medication relative to when the cough began?”
Chronic Bronchitis	Productive cough most days, smoking history, morning sputum	“Do you bring up phlegm most days?” “How long has this been going on?” “Do you smoke or have you smoked in the past?”
Bronchiectasis	Copious daily sputum, recurrent respiratory infections, often childhood onset	“How much sputum do you produce daily — a teaspoon, tablespoon, or more?” “Have you had many chest infections over the years?” “Any history of severe childhood pneumonia, tuberculosis, or cystic fibrosis?”
Pertussis	Paroxysmal cough, inspiratory whoop, post-tussive vomiting, prolonged course	“Do you have violent coughing fits that leave you exhausted?” “Do you ever vomit after coughing?” “Do you make a whooping sound when catching your breath?”
Lung Cancer	New or changed cough in smoker, hemoptysis, weight loss, chest pain	“Has the character of your usual cough changed recently?” “Have you coughed up any blood?” “Any unexplained weight loss or loss of appetite?”
Interstitial Lung Disease	Dry cough, progressive exertional dyspnea, occupational exposures, connective tissue disease	“Are you more breathless with activity than you used to be?” “Any exposure to dusts, molds, or birds?” “Do you have any autoimmune conditions like rheumatoid arthritis?”
Heart Failure	Orthopnea, paroxysmal nocturnal dyspnea, peripheral edema, known cardiac disease	“How many pillows do you sleep with?” “Do you wake up at night gasping for air?” “Have you noticed your ankles swelling?”

Medication and Exposure History

Medications That Cause Cough

Angiotensin-converting enzyme (ACE) inhibitors — Most common drug-induced cause; affects 5-20% of patients; dry, tickling cough; can occur days to months after initiation; more common in women and Asian populations. Examples: lisinopril, enalapril, ramipril, captopril
Non-selective beta-blockers — May cause bronchospasm in susceptible individuals (asthma, chronic obstructive pulmonary disease). Examples: propranolol, nadolol, timolol (including eye drops)
Inhaled medications — Dry powder inhalers and some nebulized medications can irritate airways
Nitrofurantoin — Can cause acute or chronic pulmonary toxicity with cough
Methotrexate — Hypersensitivity pneumonitis
Amiodarone — Pulmonary toxicity with chronic use
Bleomycin and other chemotherapeutic agents — Pulmonary fibrosis

Social and Occupational History

Smoking: Quantify in pack-years (packs per day × years smoked). Active smoking causes chronic bronchitis; former smokers remain at elevated cancer risk. Include cannabis use, vaping, and secondhand smoke exposure.
Occupation: Asbestos exposure (construction, shipyards, insulation), coal dust (miners), silica (sandblasting, foundries), organic dusts (farmers, grain handlers), chemical fumes (manufacturing)
Environment: Mold exposure, air quality, heating systems, humidifiers, new carpets or renovations, air conditioning (Legionella)
Travel: Endemic mycoses (histoplasmosis in Ohio/Mississippi River valleys, coccidioidomycosis in southwestern United States), tuberculosis in high-prevalence areas
Pets and Hobbies: Birds (hypersensitivity pneumonitis from avian proteins), hot tubs (mycobacterial infection), farming (farmer’s lung)
Tuberculosis risk factors: Immigration from endemic areas, incarceration, homelessness, HIV infection, healthcare work

Previous Treatments and Response

Treatment History Guides Diagnosis

Always ask what treatments have been tried and whether they helped:

Antihistamines/decongestants improved cough — Supports upper airway cough syndrome
Bronchodilator (salbutamol) provided relief — Suggests asthma component
Proton pump inhibitor helped — Supports gastroesophageal reflux disease (though may take 2-3 months)
Antibiotics helped — May indicate bacterial infection, but improvement could be coincidental with viral illness resolution
Nothing has helped despite multiple trials — Consider missed diagnosis, multiple causes, cough hypersensitivity syndrome, or inadequate treatment duration

Important: Ask about duration of each treatment trial. Many treatments require weeks to months for full effect (inhaled corticosteroids: 6-8 weeks; proton pump inhibitors: 2-3 months).

4. Physical Examination

A systematic head-to-toe approach for patients with cough

Systematic Framework: Use the “Head to Extremities” approach for complete examination of patients presenting with cough. While the respiratory system is the primary focus, extra-pulmonary findings often provide crucial diagnostic clues. Remember that a normal examination does not exclude significant pathology.

General Inspection

Begin your assessment from the moment the patient enters the room:

Appearance: Well or unwell? Comfortable at rest or in distress? Cachectic (malignancy, chronic disease) or obese (obstructive sleep apnea, reflux)?
Respiratory effort: Tachypnea, use of accessory muscles, pursed-lip breathing, tripod positioning, inability to speak in full sentences
Color: Central cyanosis (lips, tongue), peripheral cyanosis, pallor, plethora
Cough character during examination: Listen for dry versus productive, barking, whooping, or honking quality
Voice: Hoarseness (laryngeal pathology, recurrent laryngeal nerve palsy), stridor (upper airway obstruction)
Sputum: If patient produces sputum during visit, note color, consistency, volume, and any blood

Vital Signs

Vital signs are frequently overlooked but provide essential diagnostic and prognostic information:

Vital Sign	What to Look For	Clinical Significance
Temperature	Fever (greater than 38°C / 100.4°F), hypothermia in severe sepsis	Fever suggests infection (pneumonia, bronchitis, tuberculosis); absence does not exclude infection, especially in elderly or immunocompromised
Heart Rate	Tachycardia (greater than 100 beats per minute), irregularity	Tachycardia indicates physiological stress (infection, hypoxia, pain, anxiety); atrial fibrillation may suggest underlying heart failure or thyroid disease
Blood Pressure	Hypotension (sepsis), hypertension (may indicate target organ when on antihypertensives)	Hypotension with infection is concerning for sepsis; note if on angiotensin-converting enzyme inhibitors
Respiratory Rate	Tachypnea (greater than 20 breaths per minute in adults)	Often the first vital sign to change in respiratory illness; greater than 24 breaths per minute is concerning; normal rate does not exclude significant pathology
Oxygen Saturation	Less than 94% on room air is abnormal; less than 90% requires supplemental oxygen	Desaturation indicates significant respiratory compromise; normal saturation does not exclude disease; can be falsely normal in anemia or carbon monoxide poisoning

Head, Eyes, Ears, Nose, and Throat Examination

Ears

External canal: Cerumen impaction (Arnold’s nerve reflex), foreign body, otitis externa
Tympanic membrane: Otitis media with effusion (suggests eustachian tube dysfunction, allergies)

Nose

Mucosa: Pale, boggy turbinates (allergic rhinitis); erythematous, edematous (infectious rhinitis)
Discharge: Clear (allergic or viral); purulent (bacterial sinusitis)
Septal deviation or polyps: May contribute to chronic rhinosinusitis

Eyes

Conjunctival injection: Allergies, viral infection
Allergic shiners: Dark circles under eyes (chronic allergies)
Subconjunctival hemorrhage: Complication of severe coughing

Oropharynx

Posterior pharynx: Cobblestoning (chronic post-nasal drip), mucus or purulent secretions draining posteriorly
Tonsillar enlargement: Infection, obstruction
Dental health: Poor dentition may predispose to aspiration pneumonia

Neck Examination

Lymphadenopathy: Anterior cervical (upper respiratory infection), posterior cervical (mononucleosis), supraclavicular (concerning for malignancy — Virchow’s node on left)
Thyroid: Goiter may cause tracheal compression; thyroid disease associated with both cardiac and respiratory conditions
Trachea: Midline position; deviation suggests mediastinal shift (effusion, pneumothorax, mass)
Jugular venous pressure: Elevated in heart failure, cor pulmonale, pericardial disease, superior vena cava obstruction

Respiratory Examination

Inspection

Chest wall shape: Barrel chest (hyperinflation in chronic obstructive pulmonary disease), kyphoscoliosis (restrictive defect), pectus deformities
Chest wall movement: Symmetry of expansion; reduced movement on affected side (effusion, pneumothorax, consolidation)
Intercostal recession: Indicates increased work of breathing
Scars: Previous thoracic surgery, chest tube sites

Palpation

Chest expansion: Place hands on chest wall with thumbs at midline; reduced expansion on affected side localizes pathology
Tactile vocal fremitus: Increased over consolidation; decreased over effusion or pneumothorax
Chest wall tenderness: Musculoskeletal cause, rib fracture from coughing (especially in osteoporosis)
Subcutaneous emphysema: Crepitus suggesting air leak (pneumothorax, esophageal rupture after severe vomiting from coughing paroxysms)

Percussion

Resonant: Normal lung
Dull: Consolidation, effusion, mass, atelectasis
Hyperresonant: Pneumothorax, emphysema, asthma with air trapping
Stony dull: Large pleural effusion

Auscultation

Listen systematically in all lung zones, comparing side to side:

Finding	Description	Associated Conditions
Normal breath sounds	Vesicular (soft, low-pitched, inspiration longer than expiration) over lung fields; bronchial (loud, high-pitched) over trachea	Normal examination — does not exclude asthma, gastroesophageal reflux disease, upper airway cough syndrome, angiotensin-converting enzyme inhibitor cough
Polyphonic wheeze	Multiple musical pitches, predominantly expiratory	Asthma, chronic obstructive pulmonary disease, bronchitis — indicates diffuse airway narrowing
Monophonic wheeze	Single fixed pitch, may be inspiratory or expiratory	Fixed airway obstruction — tumor, foreign body, bronchial stenosis
Stridor	High-pitched, predominantly inspiratory, heard over neck	Upper airway obstruction — laryngeal edema, tumor, foreign body, vocal cord dysfunction (requires urgent evaluation)
Fine crackles (rales)	High-pitched, discontinuous sounds like Velcro; typically end-inspiratory	Interstitial lung disease (pulmonary fibrosis), early pulmonary edema, atelectasis
Coarse crackles	Low-pitched, bubbling sounds; early inspiratory or throughout inspiration	Bronchiectasis, pneumonia, severe pulmonary edema, secretions in large airways
Bronchial breath sounds over lung fields	Loud, high-pitched, with equal inspiratory and expiratory phases; heard away from central airways	Consolidation (pneumonia) — air-filled bronchi transmitting sound through solid lung tissue
Absent breath sounds	Markedly reduced or absent air entry	Large pleural effusion, pneumothorax, severe hyperinflation, mucus plugging with atelectasis
Pleural friction rub	Creaking, grating sound; heard in both inspiration and expiration	Pleuritis (infection, pulmonary embolism, malignancy, connective tissue disease)

Cardiovascular Examination

Cardiac disease is an important and frequently overlooked cause of cough:

Jugular venous pressure: Elevated in right heart failure, cor pulmonale (from chronic lung disease)
Apex beat: Displaced laterally in cardiomegaly; heaving quality suggests left ventricular hypertrophy
Heart sounds: Third heart sound (S3 gallop) indicates volume overload/heart failure; fourth heart sound (S4) suggests stiff ventricle
Murmurs: Mitral regurgitation and mitral stenosis can cause pulmonary congestion and cough
Peripheral edema: Bilateral pitting edema suggests heart failure; unilateral may indicate deep vein thrombosis (consider pulmonary embolism)

Abdominal Examination

Obesity: Associated with gastroesophageal reflux disease, obstructive sleep apnea, obesity hypoventilation syndrome
Hepatomegaly: May indicate right heart failure with hepatic congestion
Ascites: Advanced heart failure, liver disease (hepatopulmonary syndrome), malignancy
Hernias: May be complication of chronic cough; check inguinal and umbilical regions
Epigastric tenderness: May suggest gastroesophageal reflux disease, peptic ulcer disease

Extremities

Digital clubbing: Loss of nail bed angle, increased nail curvature, sponginess of nail bed. Suggests lung cancer, bronchiectasis, interstitial lung disease, cyanotic heart disease, infective endocarditis. Not seen in chronic obstructive pulmonary disease or asthma.
Peripheral cyanosis: Blue discoloration of fingers and toes; indicates poor perfusion or hypoxemia
Nicotine staining: Yellow-brown discoloration of fingers; indicates ongoing tobacco use
Peripheral edema: Pitting edema of ankles suggests heart failure or cor pulmonale
Joint abnormalities: Rheumatoid arthritis and other connective tissue diseases associated with interstitial lung disease
Asterixis: Flapping tremor may indicate carbon dioxide retention in severe respiratory failure

Expected Findings by Etiology

Condition	General	Respiratory	Other Key Findings
Upper Airway Cough Syndrome	Usually well-appearing	Often normal; may have rhonchi that clear with coughing	Cobblestoned posterior pharynx, nasal mucosal changes, post-nasal drip visible
Asthma	May be normal between attacks	Polyphonic expiratory wheeze (may be absent if mild or severe); prolonged expiratory phase	Signs of atopy (eczema, allergic rhinitis); normal examination common in cough-variant asthma
Gastroesophageal Reflux Disease	Often obese; otherwise well-appearing	Usually entirely normal	Dental erosions (severe reflux); pharyngeal erythema; epigastric tenderness
Chronic Obstructive Pulmonary Disease	Barrel chest, pursed-lip breathing, use of accessory muscles	Diffuse wheeze, prolonged expiration, decreased breath sounds, hyperresonance	Nicotine staining, peripheral cyanosis in advanced disease; no clubbing
Pneumonia	Febrile, tachypneic, may appear toxic	Focal crackles, bronchial breathing, dullness to percussion, increased fremitus	Fever, tachycardia; confusion in elderly
Bronchiectasis	May have daily productive cough	Coarse crackles, often at lung bases; may have wheeze	Clubbing (advanced cases); copious purulent sputum production
Interstitial Lung Disease	Progressive dyspnea on exertion	Fine, late inspiratory “Velcro-like” crackles at bases; may progress up lung fields	Clubbing; may have features of underlying connective tissue disease
Heart Failure	Orthopnea, paroxysmal nocturnal dyspnea	Bibasilar crackles, may have wheeze (“cardiac asthma”)	Elevated jugular venous pressure, S3 gallop, displaced apex, peripheral edema
Lung Cancer	May have weight loss, cachexia	May be normal; may have focal findings (mass effect), lymphangitic spread (crackles), effusion	Clubbing, supraclavicular lymphadenopathy, Horner syndrome, hoarseness
Angiotensin-Converting Enzyme Inhibitor Cough	Well-appearing	Entirely normal	No physical examination findings; diagnosis is clinical

Important Teaching Point: Normal Examination is Common!

Many of the most common causes of chronic cough present with entirely normal physical examination findings. This includes:

Upper airway cough syndrome — Posterior pharynx may appear normal between episodes
Cough-variant asthma — No wheeze audible when not actively symptomatic
Gastroesophageal reflux disease — Physical examination is typically unremarkable
Angiotensin-converting enzyme inhibitor-induced cough — No examination abnormalities
Non-asthmatic eosinophilic bronchitis — Normal examination

A normal physical examination does not exclude significant pathology and should not provide false reassurance. The history remains the most valuable diagnostic tool in evaluating cough.

5. Differential Diagnosis

Systematic approach organized by probability and clinical features

The differential diagnosis of cough is best organized by duration, as this single factor dramatically changes the probability of various etiologies. Within each duration category, conditions are further organized by probability to guide clinical reasoning and investigation.

Acute Cough (Duration: Less Than 3 Weeks)

Acute cough is overwhelmingly infectious in etiology. The primary clinical challenge is distinguishing self-limiting viral illness from conditions requiring specific treatment or urgent intervention.

Probability	Condition	Key Features	Red Flags
COMMON (approximately 80%)	Viral Upper Respiratory Tract Infection	Rhinorrhea, sore throat, low-grade fever, malaise; self-limiting over 7-10 days; cough may persist 2-3 weeks	High fever, severe symptoms, immunocompromised host
	Acute Bronchitis	Cough (productive or dry), chest discomfort, low-grade fever; usually viral; typically resolves in 1-3 weeks	Persistent high fever, dyspnea, focal chest findings suggesting pneumonia
	Acute Exacerbation of Asthma	Known asthmatic with increased cough, wheeze, dyspnea; often triggered by viral infection	Severe dyspnea, inability to speak sentences, silent chest, cyanosis
	Acute Exacerbation of Chronic Obstructive Pulmonary Disease	Increased cough, sputum volume and purulence, worsening dyspnea in known chronic obstructive pulmonary disease patient	Severe dyspnea, confusion, cyanosis, use of accessory muscles
LESS COMMON (approximately 15%)	Community-Acquired Pneumonia	Productive cough, fever, dyspnea, pleuritic chest pain; focal crackles and dullness on examination	High fever, rigors, tachypnea, hypoxia, confusion (especially elderly)
	Influenza	Abrupt onset, high fever, severe myalgias, headache, dry cough; seasonal pattern	Dyspnea, persistent fever, worsening after initial improvement (secondary bacterial infection)
	COVID-19	Dry cough, fever, fatigue, loss of taste/smell; variable severity; may progress to pneumonia	Dyspnea, hypoxia, persistent fever, chest pain
UNCOMMON BUT SERIOUS (approximately 5%)	Pulmonary Embolism	Sudden dyspnea, pleuritic chest pain, cough (may be dry or with hemoptysis); risk factors for venous thromboembolism	Hemoptysis, syncope, hypotension, severe hypoxia
	Acute Heart Failure	Dyspnea, orthopnea, paroxysmal nocturnal dyspnea, cough worse when lying flat; pink frothy sputum in severe cases	Severe dyspnea, hypoxia, pink frothy sputum, hypotension
	Foreign Body Aspiration	Sudden onset cough, choking episode; may have unilateral wheeze or decreased breath sounds	Stridor, severe respiratory distress, cyanosis
	Pertussis (Early Catarrhal Phase)	Mild cough, rhinorrhea resembling common cold; highly contagious; progresses to paroxysmal phase	Household contacts, unvaccinated status, healthcare worker exposure

Subacute Cough (Duration: 3 to 8 Weeks)

Subacute cough most commonly represents post-infectious cough following a viral upper respiratory tract infection. However, pertussis is frequently missed in this category and should be considered in any patient with prolonged cough, particularly if paroxysmal.

Probability	Condition	Key Features	Expected Course
COMMON (approximately 70%)	Post-Infectious Cough	Cough persisting after resolution of acute upper respiratory tract infection; no fever; gradually improving	Resolves spontaneously over 3-8 weeks; may respond to inhaled corticosteroids or ipratropium
COMMON (approximately 70%)	Unrecognized Asthma or Chronic Obstructive Pulmonary Disease	Cough triggered or unmasked by recent respiratory infection; may have subtle wheeze, prolonged expiration	Persists until appropriately treated; responds to bronchodilators and inhaled corticosteroids
LESS COMMON (approximately 20%)	Pertussis (Whooping Cough)	Paroxysmal cough with inspiratory “whoop,” post-tussive vomiting, cough lasting weeks to months; often called “100-day cough”	Paroxysmal phase lasts 2-8 weeks; convalescent phase with gradually diminishing cough can last months
LESS COMMON (approximately 20%)	Bacterial Sinusitis	Cough with purulent nasal discharge, facial pain/pressure, symptoms worsening after initial improvement or lasting more than 10 days	Responds to antibiotics; untreated may persist or lead to complications
UNCOMMON (approximately 10%)	Slowly Resolving Pneumonia	Persistent cough after treated pneumonia; radiographic abnormalities may persist 6-8 weeks	Gradual improvement; failure to improve should prompt evaluation for complications or alternative diagnosis
UNCOMMON (approximately 10%)	New Presentation of Chronic Cough Etiology	Upper airway cough syndrome, asthma, or gastroesophageal reflux disease presenting for first time or newly symptomatic	Persists beyond 8 weeks if untreated; becomes chronic cough

Chronic Cough (Duration: Greater Than 8 Weeks)

Step-by-Step Approach to Chronic Cough:

Step 1: Rule out obvious causes — Is the patient taking an angiotensin-converting enzyme inhibitor? Is the patient a current smoker? Is the chest radiograph abnormal?
Step 2: Consider “The Big Three” — Upper airway cough syndrome, asthma, and gastroesophageal reflux disease account for more than 90% of chronic cough in non-smokers with normal chest radiograph
Step 3: Investigate systematically — If initial evaluation is unrevealing, pursue targeted investigations for less common causes
Step 4: Consider multiple etiologies — Up to 25% of patients have more than one cause; all must be addressed for resolution

Probability	Condition	Approximate Frequency	Key Distinguishing Features
COMMON	Upper Airway Cough Syndrome (Post-Nasal Drip Syndrome)	20-40%	Sensation of secretions in throat, frequent throat clearing, nasal congestion; cobblestoned posterior pharynx; responds to antihistamines/decongestants
	Asthma (including Cough-Variant Asthma)	20-30%	Episodic symptoms, nocturnal cough, triggers (cold air, exercise, allergens); may have no wheeze; responds to bronchodilators and inhaled corticosteroids
	Gastroesophageal Reflux Disease	10-40%	Cough worse after meals or when supine; up to 75% have “silent reflux” without heartburn; requires prolonged proton pump inhibitor trial (2-3 months)
	Non-Asthmatic Eosinophilic Bronchitis	10-15%	Chronic cough with sputum eosinophilia but no airway hyperresponsiveness; normal spirometry and methacholine challenge; responds to inhaled corticosteroids
	Angiotensin-Converting Enzyme Inhibitor-Induced Cough	Variable (5-20% of those on these medications)	Dry, tickling cough; onset days to months after starting medication; more common in women and Asian populations; resolves 1-4 weeks after stopping
LESS COMMON	Chronic Bronchitis	5-10%	Productive cough most days for at least 3 months in 2 consecutive years; smoking history; morning sputum production
	Bronchiectasis	3-5%	Copious daily purulent sputum (often greater than 25 mL/day); recurrent respiratory infections; may have clubbing; high-resolution computed tomography diagnostic
	Chronic Obstructive Pulmonary Disease	Variable	Smoking history, dyspnea, productive cough; airflow obstruction on spirometry; often overlaps with chronic bronchitis
	Obstructive Sleep Apnea	Variable	Snoring, witnessed apneas, daytime somnolence, morning headaches; obesity; cough may be due to associated reflux or airway inflammation
UNCOMMON BUT IMPORTANT	Lung Cancer	2-5%	New or changed cough in smoker; hemoptysis, weight loss, chest pain; may present as post-obstructive pneumonia
	Interstitial Lung Disease	Variable	Progressive exertional dyspnea, dry cough; fine inspiratory crackles; clubbing; restrictive pattern on spirometry; ground-glass or reticular changes on imaging
	Tuberculosis	Variable (depends on population)	Chronic cough, night sweats, weight loss, hemoptysis; risk factors: immigration from endemic areas, immunosuppression, incarceration, homelessness
	Heart Failure	Variable	Orthopnea, paroxysmal nocturnal dyspnea, peripheral edema; cough worse when supine; elevated jugular venous pressure, S3 gallop
	Cough Hypersensitivity Syndrome	Variable	Heightened cough reflex; triggered by low-level stimuli (talking, laughing, scents); laryngeal paresthesia; often diagnosis of exclusion after treating other causes

Anatomical Approach to Chronic Cough

Organizing the differential by anatomical location can help ensure comprehensive consideration of all potential causes:

Upper Airway

Upper airway cough syndrome (post-nasal drip)

Allergic rhinitis

Chronic sinusitis

Vasomotor rhinitis

Laryngopharyngeal reflux

Vocal cord dysfunction

Central Airways

Asthma and cough-variant asthma

Chronic bronchitis

Bronchiectasis

Endobronchial tumor

Foreign body

Tracheobronchomalacia

Lung Parenchyma

Interstitial lung disease

Lung cancer

Chronic infection (tuberculosis, non-tuberculous mycobacteria)

Sarcoidosis

Hypersensitivity pneumonitis

Eosinophilic pneumonia

Extra-Pulmonary

Gastroesophageal reflux disease

Heart failure

Pericardial disease

Angiotensin-converting enzyme inhibitor-induced

Arnold’s nerve reflex (ear canal)

Psychogenic/habit cough

Drug-Induced Cough

Always review the medication list in any patient with chronic cough. The following medications are known to cause or exacerbate cough:

Drug or Drug Class	Mechanism	Characteristics	Time to Resolution After Stopping
Angiotensin-Converting Enzyme (ACE) Inhibitors (lisinopril, enalapril, ramipril, captopril, benazepril, perindopril)	Accumulation of bradykinin and substance P in airways due to inhibition of their degradation	Dry, tickling, non-productive cough; can occur within days or up to years after starting; not dose-dependent; affects 5-20% of patients; more common in women, Asian populations	Usually 1-4 weeks; may take up to 3 months in some cases
Angiotensin Receptor Blockers (ARBs) (losartan, valsartan, irbesartan)	Rarely cause cough as they do not affect bradykinin metabolism; however, small percentage of ACE inhibitor cough patients may also cough with ARBs	Much less common than ACE inhibitors (less than 1%); safe alternative in most patients with ACE inhibitor cough	Similar to ACE inhibitors if occurs
Non-Selective Beta-Blockers (propranolol, nadolol, timolol including eye drops)	Block beta-2 receptors in bronchial smooth muscle, causing bronchoconstriction in susceptible individuals	Bronchospasm, wheeze, and cough; primarily in patients with underlying asthma or chronic obstructive pulmonary disease; even topical (eye drops) can cause systemic effects	Days to weeks after discontinuation
Inhaled Medications (dry powder inhalers, some nebulized medications)	Direct irritation of airways; lactose in dry powder inhalers; preservatives in nebulized solutions	Cough immediately following inhalation; may limit adherence to inhaler therapy	Immediate with change to alternative formulation
Nitrofurantoin	Acute hypersensitivity reaction or chronic interstitial pneumonitis	Acute: fever, dyspnea, cough within days to weeks; Chronic: insidious onset with prolonged use	Acute: days to weeks; Chronic: may be incomplete
Methotrexate	Hypersensitivity pneumonitis; not dose-dependent	Subacute onset of dyspnea, dry cough, fever; ground-glass infiltrates on imaging	Weeks to months; may require corticosteroids
Amiodarone	Direct pulmonary toxicity; accumulates in lung tissue	Insidious onset of cough, dyspnea; typically with cumulative dose; may present as interstitial pneumonitis or organizing pneumonia	Months (drug has very long half-life); may be permanent
Sirolimus / Everolimus	Drug-induced interstitial lung disease	Progressive cough, dyspnea; seen in transplant patients and those on mTOR inhibitors for cancer	Variable; may require dose reduction or discontinuation
Chemotherapeutic Agents (bleomycin, busulfan, cyclophosphamide)	Direct pulmonary toxicity leading to pneumonitis or fibrosis	Progressive dyspnea and dry cough; dose-dependent for some agents (bleomycin); may be irreversible	Variable; fibrosis may be permanent
Targeted Therapies and Immunotherapy (checkpoint inhibitors, TKIs)	Immune-mediated pneumonitis (checkpoint inhibitors); interstitial lung disease (tyrosine kinase inhibitors)	Variable onset; may be severe; requires high index of suspicion	Variable; often requires corticosteroids

Quick Reference: “If You See This, Think This”

Use these clinical clues to rapidly narrow your differential:

Clinical Clue	Think This First	Next Step
Patient on ACE inhibitor	ACE inhibitor-induced cough	Stop ACE inhibitor, switch to ARB; reassess in 1-4 weeks
Current smoker with chronic productive cough	Chronic bronchitis; consider lung cancer if new or changed	Chest radiograph; spirometry; smoking cessation; low-dose CT if meets screening criteria
Throat clearing, post-nasal drip sensation	Upper airway cough syndrome	Trial of first-generation antihistamine plus decongestant
Cough worse at night or with exercise, cold air	Asthma or cough-variant asthma	Spirometry with bronchodilator response; consider methacholine challenge; trial of inhaled corticosteroid
Cough worse after meals or when lying down	Gastroesophageal reflux disease	Empiric proton pump inhibitor twice daily for 2-3 months; lifestyle modifications
Paroxysmal cough with vomiting or inspiratory whoop	Pertussis	Nasopharyngeal swab for PCR/culture; macrolide antibiotic
Hemoptysis in smoker or former smoker	Lung cancer until proven otherwise	Urgent chest CT; bronchoscopy if indicated
Progressive exertional dyspnea with dry cough	Interstitial lung disease	High-resolution chest CT; pulmonary function tests; consider rheumatologic workup
Night sweats, weight loss, hemoptysis, TB risk factors	Tuberculosis	Chest radiograph; sputum for acid-fast bacilli smear and culture; airborne isolation
Orthopnea, peripheral edema, S3 gallop	Heart failure	Echocardiogram; BNP/NT-proBNP; chest radiograph
Copious daily purulent sputum production	Bronchiectasis	High-resolution chest CT; sputum culture
Cough triggered by ear examination or hearing aid	Arnold’s nerve reflex	Examine ears; remove cerumen impaction or irritating hearing aid component

6. Diagnostic Investigations

A stepwise, cost-effective approach guided by clinical suspicion

The approach to investigating cough depends on its duration and the clinical context. For acute cough, investigations are often unnecessary unless red flags are present. For chronic cough, a systematic approach focusing on the most common causes yields the highest diagnostic return.

Baseline Investigations for Chronic Cough

These investigations should be considered for all patients with chronic cough to exclude common and serious etiologies:

Investigation	Purpose	What to Look For	Practical Points
Chest Radiograph (Posteroanterior and Lateral)	Exclude parenchymal disease, mass lesions, cardiomegaly, pleural abnormalities	Mass, infiltrate, interstitial changes, cardiomegaly, pleural effusion, hilar adenopathy	Essential first-line test; normal result narrows differential significantly but does not exclude all causes; abnormal result directs further workup
Spirometry	Detect airflow obstruction (asthma, chronic obstructive pulmonary disease) or restriction	FEV1/FVC ratio less than 0.7 indicates obstruction; significant bronchodilator response (greater than 12% and greater than 200 mL increase in FEV1) suggests asthma	Normal spirometry does not exclude asthma (may be normal between episodes); consider bronchoprovocation testing if high suspicion
Complete Blood Count	Screen for infection, eosinophilia, anemia	Leukocytosis (infection); eosinophilia (asthma, eosinophilic bronchitis, parasites); anemia (chronic disease, malignancy)	Peripheral eosinophilia supports allergic or eosinophilic airway disease but is not always present

Targeted Investigations by Suspected Etiology

If Suspecting Upper Airway Cough Syndrome

First-Line Approach

Empiric treatment trial: First-generation antihistamine (chlorpheniramine or diphenhydramine) plus decongestant for 2-3 weeks is both diagnostic and therapeutic
Response confirms diagnosis — No imaging needed if patient improves
Nasal endoscopy: If available, can visualize post-nasal drip, polyps, or anatomical abnormalities

Second-Line Tests (If No Response)

Sinus CT scan: Evaluate for chronic sinusitis, anatomical abnormalities, polyps; reserve for treatment failures or suspected complications
Allergy testing: Skin prick tests or specific IgE for environmental allergens if allergic rhinitis suspected
Nasal cytology: Eosinophils suggest allergic rhinitis; neutrophils suggest infection

If Suspecting Asthma or Cough-Variant Asthma

First-Line Tests

Spirometry with bronchodilator response: FEV1 increase of greater than 12% AND greater than 200 mL after bronchodilator confirms reversible obstruction
Peak flow monitoring: Diurnal variation greater than 20% suggests asthma; have patient record morning and evening readings for 2 weeks
Empiric trial of inhaled corticosteroid: Response within 6-8 weeks supports diagnosis of asthma

Second-Line Tests

Methacholine challenge test: Positive if PC20 (concentration causing 20% fall in FEV1) is less than 4 mg/mL; high sensitivity (greater than 95%) — negative result essentially excludes current asthma
Fractional exhaled nitric oxide (FeNO): Greater than 50 parts per billion in untreated patient suggests eosinophilic airway inflammation; supports asthma diagnosis; useful for monitoring
Induced sputum for eosinophils: Eosinophils greater than 3% supports asthma or eosinophilic bronchitis

If Suspecting Non-Asthmatic Eosinophilic Bronchitis

Diagnostic Criteria

Chronic cough as the predominant symptom
Sputum eosinophilia: Greater than 3% eosinophils on induced sputum
Normal spirometry: No airflow obstruction
Negative bronchoprovocation: Normal methacholine challenge (distinguishes from asthma)

Key Distinction from Asthma

No bronchial hyperresponsiveness — This is the key differentiating feature
Responds to inhaled corticosteroids — Like asthma, responds well to anti-inflammatory therapy
Does not respond to bronchodilators — No benefit from beta-agonists

If Suspecting Gastroesophageal Reflux Disease

First-Line Approach

Empiric proton pump inhibitor trial: High-dose proton pump inhibitor (twice daily dosing) for at least 2-3 months; this is the recommended initial approach
Lifestyle modifications: Weight loss, avoid eating before bed, elevate head of bed, avoid trigger foods
Response to therapy: Improvement confirms reflux as contributor; note that cough may take 2-3 months to resolve

Second-Line Tests (If No Response or Diagnosis Uncertain)

24-hour esophageal pH monitoring: Gold standard; quantifies acid exposure; correlates reflux events with cough episodes; DeMeester score greater than 14.7 is abnormal
Combined pH-impedance monitoring: Detects both acid and non-acid reflux; more sensitive than pH monitoring alone
Upper endoscopy: Visualize esophagitis, Barrett’s esophagus; normal endoscopy does not exclude reflux-related cough
Barium swallow: May show hiatal hernia or anatomical abnormality but limited sensitivity for reflux

If Suspecting Bronchiectasis

Diagnostic Imaging

High-resolution chest CT: Diagnostic study of choice; shows bronchial dilation (internal diameter greater than accompanying artery), bronchial wall thickening, “signet ring sign,” lack of normal tapering
Chest radiograph: May show “tram-track” lines, ring shadows, but sensitivity is low; often normal in mild disease

Etiological Workup

Sputum culture: Identify colonizing organisms (Pseudomonas aeruginosa, Haemophilus influenzae, non-tuberculous mycobacteria)
Immunoglobulin levels: Screen for immunodeficiency (IgG, IgA, IgM)
Consider: Cystic fibrosis testing (sweat chloride), ciliary function testing, alpha-1 antitrypsin level, rheumatoid factor/autoimmune panel

If Suspecting Lung Cancer or Serious Pulmonary Pathology

Imaging

Chest CT with contrast: Detailed evaluation of mass lesions, lymphadenopathy, mediastinal involvement
PET-CT: Staging for known or suspected malignancy; identifies metabolically active lesions

Tissue Diagnosis

Bronchoscopy: Direct visualization; bronchoalveolar lavage; endobronchial biopsy; transbronchial biopsy
CT-guided biopsy: For peripheral lesions not accessible by bronchoscopy
Sputum cytology: Limited sensitivity but non-invasive; may identify central tumors

If Suspecting Interstitial Lung Disease

First-Line Tests

High-resolution chest CT: Characterize pattern of disease (usual interstitial pneumonia pattern, non-specific interstitial pneumonia, organizing pneumonia, hypersensitivity pneumonitis)
Pulmonary function tests: Typically show restrictive pattern (reduced total lung capacity, FVC) with reduced diffusing capacity (DLCO)

Further Evaluation

Autoimmune panel: ANA, rheumatoid factor, anti-CCP, myositis panel (interstitial lung disease may be first manifestation of connective tissue disease)
Hypersensitivity pneumonitis panel: Precipitins to common antigens (birds, molds)
Bronchoscopy with bronchoalveolar lavage: Cell differential can help characterize disease
Surgical lung biopsy: May be required for definitive diagnosis in unclear cases

Empiric Treatment Trials as Diagnostic Tools

Sequential Empiric Therapy Approach

When the diagnosis is unclear and initial investigations are unrevealing, empiric treatment trials serve as both diagnostic and therapeutic interventions. Response to specific therapy supports the corresponding diagnosis. This approach is particularly useful for “The Big Three” causes of chronic cough.

Trial 1 — Upper Airway Cough Syndrome: First-generation antihistamine (chlorpheniramine 4 mg three times daily or diphenhydramine 25 mg three times daily) plus decongestant (pseudoephedrine 60 mg three times daily) for 2-3 weeks. Second-generation antihistamines are less effective for cough.
Trial 2 — Asthma: Inhaled corticosteroid (beclomethasone, budesonide, or fluticasone at moderate dose) with or without long-acting beta-agonist for 6-8 weeks. Response supports asthma diagnosis.
Trial 3 — Gastroesophageal Reflux Disease: Proton pump inhibitor twice daily (omeprazole 20 mg, lansoprazole 30 mg, or equivalent, taken 30 minutes before breakfast and dinner) for 2-3 months. Cough improvement may be gradual.

Important considerations:

Ensure adequate duration of each trial before concluding treatment failure
Multiple causes may coexist — partial response suggests additional contributing factors
Patient adherence is crucial — confirm compliance before labeling treatment as unsuccessful

Investigation Summary by Cough Duration

Duration	Routine Investigations	Investigations for Red Flags
Acute (less than 3 weeks)	Usually none required; self-limiting illness presumed	Chest radiograph if pneumonia suspected; oxygen saturation; consider D-dimer/CT angiography if pulmonary embolism suspected; COVID-19/influenza testing if indicated
Subacute (3-8 weeks)	Chest radiograph if not improving; consider pertussis testing (nasopharyngeal PCR) if paroxysmal cough or epidemic exposure	As above; chest CT if abnormal radiograph or high concern for serious pathology
Chronic (greater than 8 weeks)	Chest radiograph; spirometry; review medication list for ACE inhibitors; complete blood count	Chest CT (if smoker, hemoptysis, abnormal radiograph); bronchoscopy if suspicious for malignancy or foreign body; high-resolution CT if interstitial lung disease suspected

Key Diagnostic Thresholds and Values

Test	Diagnostic Threshold	Interpretation
Spirometry — Airflow Obstruction	FEV1/FVC ratio less than 0.7	Confirms obstructive pattern (asthma, chronic obstructive pulmonary disease)
Spirometry — Bronchodilator Response	Greater than 12% AND greater than 200 mL improvement in FEV1	Significant reversibility; supports asthma diagnosis
Methacholine Challenge	PC20 less than 4 mg/mL (moderate to severe); less than 16 mg/mL (borderline)	Positive test indicates bronchial hyperresponsiveness; high sensitivity for asthma
Fractional Exhaled Nitric Oxide (FeNO)	Greater than 50 ppb (high); 25-50 ppb (intermediate); less than 25 ppb (normal)	High value suggests eosinophilic airway inflammation; supports asthma diagnosis; useful for monitoring corticosteroid response
Induced Sputum Eosinophils	Greater than 3%	Supports asthma or non-asthmatic eosinophilic bronchitis
24-Hour Esophageal pH Monitoring	DeMeester score greater than 14.7; acid exposure time greater than 4.5%	Confirms pathological acid reflux
Peak Flow Variability	Greater than 20% diurnal variation	Supports asthma diagnosis

7. Pattern Recognition and Clinical Decision-Making

Practical algorithms and decision pathways

Effective management of cough requires systematic clinical reasoning. This section provides practical algorithms to guide decision-making from initial presentation through treatment and follow-up.

Step 1: Is This Urgent?

Before proceeding with routine evaluation, assess for features requiring immediate action:

Clinical Scenario	Urgency Level	Immediate Action
Massive hemoptysis (greater than 200 mL/24 hours), respiratory distress, stridor, or impending airway compromise	EMERGENT	Secure airway, high-flow oxygen, IV access, urgent specialist consultation (pulmonology, thoracic surgery, interventional radiology); consider intubation; position patient with bleeding lung down if known
Severe dyspnea, hypoxia (SpO2 less than 90%), hemodynamic instability, suspected pulmonary embolism	EMERGENT	Supplemental oxygen, cardiac monitoring, IV access, urgent chest imaging, consider anticoagulation if pulmonary embolism suspected; emergency department evaluation
High fever with productive cough, tachypnea, focal chest findings suggesting pneumonia	URGENT	Chest radiograph, oxygen saturation, blood cultures if febrile, initiate empiric antibiotics; assess severity (CURB-65 or PSI score); determine inpatient versus outpatient management
Hemoptysis in smoker or former smoker over age 40	URGENT	Chest radiograph immediately; if abnormal or high clinical suspicion, chest CT within days; expedited pulmonology referral; bronchoscopy if indicated
Suspected pertussis in healthcare worker or close contact of infant	URGENT	Nasopharyngeal swab for pertussis PCR; initiate macrolide antibiotic immediately (azithromycin or clarithromycin); exclude from work/contact until 5 days of antibiotic completed; contact tracing
Chronic cough with weight loss, night sweats, tuberculosis risk factors	URGENT	Chest radiograph; if suspicious, implement airborne isolation; obtain sputum for acid-fast bacilli smear and culture; public health notification if tuberculosis confirmed
Uncomplicated acute cough (less than 3 weeks) with mild symptoms, no red flags	ROUTINE	Symptomatic treatment; reassurance about expected 2-3 week duration; safety-net advice about when to return; no investigations usually required
Chronic cough (greater than 8 weeks) without red flags, non-smoker, normal chest radiograph	ROUTINE	Systematic evaluation for “Big Three” causes; review medications for ACE inhibitors; empiric treatment trials; outpatient workup appropriate

Step 2: Classify by Duration

Acute (Less Than 3 Weeks)

Most likely: Viral upper respiratory tract infection

Approach: Symptomatic treatment unless red flags present

Proceed to Algorithm A

Subacute (3-8 Weeks)

Most likely: Post-infectious cough

Approach: Consider pertussis; reassess if not improving

Proceed to Algorithm B

Chronic (Greater Than 8 Weeks)

Most likely: Upper airway cough syndrome, asthma, or gastroesophageal reflux disease

Approach: Systematic evaluation and empiric trials

Proceed to Algorithm C

Step 3: Follow the Appropriate Algorithm

Algorithm A: Acute Cough (Less Than 3 Weeks)

Clinical Scenario	Most Likely Diagnosis	Action
Rhinorrhea, sore throat, low-grade fever, mild cough; no dyspnea or focal findings	Viral upper respiratory tract infection	Symptomatic treatment (honey, dextromethorphan for adults); no antibiotics; expected resolution in 7-10 days; cough may persist 2-3 weeks
Productive cough, low-grade fever, chest discomfort; clear lungs on examination	Acute bronchitis	Symptomatic treatment; antibiotics NOT indicated for uncomplicated bronchitis; consider chest radiograph if symptoms severe or prolonged
Cough with fever, dyspnea, focal crackles, dullness to percussion	Community-acquired pneumonia	Chest radiograph to confirm; assess severity (CURB-65); initiate empiric antibiotics; hospitalize if severe
Known asthmatic with increased cough, wheeze, dyspnea following upper respiratory infection	Acute asthma exacerbation	Increase bronchodilator frequency; short course of oral corticosteroids; reassess inhaled corticosteroid dose; action plan for future exacerbations
Sudden onset dyspnea, pleuritic chest pain, risk factors for venous thromboembolism	Pulmonary embolism	Assess pre-test probability (Wells score); D-dimer if low probability; CT pulmonary angiography if elevated D-dimer or high probability; anticoagulation if confirmed
Dyspnea, orthopnea, peripheral edema, elevated jugular venous pressure, S3 gallop	Acute heart failure	Chest radiograph (pulmonary edema, cardiomegaly); BNP/NT-proBNP; echocardiogram; diuretics; treat underlying cause

Algorithm B: Subacute Cough (3-8 Weeks)

Clinical Scenario	Most Likely Diagnosis	Action
Cough persisting after resolved upper respiratory infection; gradually improving; no fever	Post-infectious cough	Reassurance (may take 8 weeks to fully resolve); consider inhaled ipratropium or short course of inhaled corticosteroid if bothersome; chest radiograph if not improving by 8 weeks
Paroxysmal cough, post-tussive vomiting, inspiratory whoop; household contacts with similar illness	Pertussis	Nasopharyngeal PCR; macrolide antibiotic (azithromycin 5 days or clarithromycin 7 days); antibiotics reduce transmission but may not shorten cough duration if started late; notify contacts
Purulent nasal discharge, facial pain/pressure, symptoms greater than 10 days or worsening after improvement	Bacterial sinusitis	Amoxicillin-clavulanate for 5-7 days; nasal saline irrigation; decongestants; consider imaging if recurrent or not responding
Persistent cough with nocturnal symptoms or exercise intolerance; personal or family history of atopy	Newly symptomatic asthma	Spirometry; trial of inhaled corticosteroid for 6-8 weeks; if responds, continue asthma management; if no response, reconsider diagnosis

Algorithm C: Chronic Cough (Greater Than 8 Weeks)

Initial Assessment for All Patients with Chronic Cough:

Review medications: Is patient on an ACE inhibitor? → Stop and switch to ARB; reassess in 1-4 weeks
Assess smoking status: Current smoker? → Smoking cessation is essential; chest radiograph required; consider lung cancer screening if eligible
Obtain chest radiograph: Abnormal? → Pursue specific diagnosis based on findings (CT, bronchoscopy, etc.)
If above are addressed/negative: Proceed with systematic evaluation for “The Big Three”

Clinical Scenario	Most Likely Diagnosis	Action
Throat clearing, sensation of post-nasal drip, nasal congestion, cobblestoned posterior pharynx	Upper airway cough syndrome	First-generation antihistamine plus decongestant for 2-3 weeks; if allergic component, add nasal corticosteroid; if no response, consider sinus CT
Cough worse at night or with exercise/cold air; wheeze; atopic history; variable symptoms	Asthma or cough-variant asthma	Spirometry with bronchodilator; if normal but high suspicion, methacholine challenge or FeNO; trial of inhaled corticosteroid for 6-8 weeks
Cough worse after meals or when supine; heartburn or regurgitation (may be absent)	Gastroesophageal reflux disease	Proton pump inhibitor twice daily for 2-3 months; lifestyle modifications; if no response, consider pH monitoring before escalating
Chronic cough with sputum eosinophilia but normal spirometry and negative methacholine challenge	Non-asthmatic eosinophilic bronchitis	Inhaled corticosteroid (responds well); does not require bronchodilators
Daily dry, tickling cough; patient on ACE inhibitor; onset days to months after starting medication	ACE inhibitor-induced cough	Discontinue ACE inhibitor; switch to ARB; cough should resolve within 1-4 weeks (may take up to 3 months)
Partial response to treatment or multiple treatments needed for resolution	Multiple etiologies (present in up to 25%)	Continue successful treatments while adding therapy for additional suspected causes; all contributing factors must be addressed

“What Do I Do If…” Decision Reference

Clinical Situation	Immediate Action	Next Step
Patient on ACE inhibitor presents with chronic dry cough	Stop ACE inhibitor today; switch to ARB for blood pressure/cardiac indication	Reassess in 1-4 weeks; if cough persists beyond 4 weeks, ACE inhibitor was likely not the only cause — continue systematic evaluation
Smoker over age 40 with new or changed cough	Obtain chest radiograph immediately; strongly encourage smoking cessation	If radiograph abnormal or high suspicion despite normal radiograph, obtain chest CT; refer for bronchoscopy if mass or suspicious lesion; ensure low-dose CT screening if meets criteria
Patient requests antibiotics for acute bronchitis	Explain that acute bronchitis is usually viral; antibiotics do not help and may cause harm	Offer symptomatic treatment; provide safety-net advice about when to return (worsening symptoms, new fever, dyspnea, symptoms beyond 3 weeks)
Chronic cough with normal chest radiograph and no response to empiric treatment for “Big Three”	Reassess diagnosis; confirm adequate treatment duration and patient adherence	Consider high-resolution chest CT; spirometry with methacholine challenge; FeNO; consider bronchoscopy; refer to pulmonology/cough specialist; consider cough hypersensitivity syndrome
Patient has tried multiple treatments with only partial improvement	Consider multiple coexisting etiologies (affects up to 25% of chronic cough patients)	Continue treatments that provided partial benefit; systematically add therapies for other suspected causes; all contributing factors must be treated for full resolution
Cough causing significant complications (incontinence, syncope, rib fracture)	Acknowledge impact on quality of life; expedite workup	Aggressive treatment of underlying cause; consider short-term cough suppression (codeine, dextromethorphan) while pursuing diagnosis; refer to specialist if refractory
Chronic cough persists despite treating all identified causes	Consider cough hypersensitivity syndrome (unexplained chronic cough)	Speech pathology/behavioral cough suppression therapy; consider trial of neuromodulatory agents (gabapentin, pregabalin, low-dose morphine) under specialist guidance

Troubleshooting Refractory Cough

Ask These Questions When Cough Does Not Respond to Treatment

Was the treatment duration adequate? — Inhaled corticosteroids require 6-8 weeks; proton pump inhibitors require 2-3 months; don’t abandon treatment prematurely
Was patient adherence good? — Confirm patient is taking medications correctly; check inhaler technique; verify twice-daily proton pump inhibitor dosing 30 minutes before meals
Were all potential causes addressed? — Up to 25% of patients have multiple etiologies; partial response suggests additional contributing factors
Is the diagnosis correct? — Reconsider if expected response not seen; obtain additional testing (methacholine challenge, pH monitoring, high-resolution CT)
Was the ACE inhibitor stopped? — Easy to overlook; cough may take up to 3 months to resolve after stopping
Is the patient still smoking? — Ongoing smoking perpetuates chronic bronchitis and inflammation
Are there less common causes? — Consider bronchiectasis, interstitial lung disease, obstructive sleep apnea, cardiac causes
Could this be cough hypersensitivity syndrome? — Heightened cough reflex sensitivity; may benefit from speech therapy or neuromodulatory agents

When to Refer to a Specialist

Scenario	Refer To	Urgency
Hemoptysis in smoker; suspected lung cancer	Pulmonology; Thoracic Surgery if operable lesion	Urgent (within days)
Suspected interstitial lung disease	Pulmonology (ideally interstitial lung disease specialist)	Soon (within 2-4 weeks)
Chronic cough not responding to standard therapy after 2-3 months	Pulmonology or Cough Specialist	Routine (within 4-6 weeks)
Chronic sinusitis not responding to medical therapy	Otolaryngology (ENT)	Routine
Gastroesophageal reflux disease not responding to aggressive proton pump inhibitor therapy	Gastroenterology	Routine
Suspected vocal cord dysfunction or laryngeal pathology	Otolaryngology; Speech-Language Pathology	Routine
Refractory cough with significant quality of life impact	Multidisciplinary cough clinic if available	Routine

8. Clinical Pearls and Pitfalls

Practical wisdom — learn from successes and avoid common mistakes

Must-Know Clinical Pearls

“The Big Three” dominate chronic cough: Upper airway cough syndrome, asthma, and gastroesophageal reflux disease account for more than 90% of chronic cough in non-smokers with a normal chest radiograph. Master these three conditions and you will successfully manage most chronic cough.

Duration is your most powerful diagnostic tool: Acute, subacute, and chronic cough have fundamentally different differential diagnoses. Always establish duration as your first step — it immediately narrows the possibilities.

Always review the medication list: ACE inhibitor-induced cough is one of the most common causes of chronic cough and is frequently overlooked. It’s easily treatable by switching to an ARB. Ask specifically about blood pressure medications by name.

Silent reflux is common: Up to 75% of patients with gastroesophageal reflux disease-related cough have no typical reflux symptoms (heartburn, regurgitation). Do not rule out reflux simply because the patient denies heartburn.

First-generation antihistamines work better for cough: For upper airway cough syndrome, older sedating antihistamines (chlorpheniramine, diphenhydramine) are more effective than newer non-sedating antihistamines (loratadine, cetirizine) due to their anticholinergic drying effect.

Check the ears: Arnold’s nerve reflex — stimulation of the external auditory canal can trigger cough in 2-4% of people. Cerumen impaction or hearing aid irritation can be a simple, treatable cause of chronic cough.

Think pertussis in subacute cough: Pertussis is frequently missed in adults. The characteristic “whoop” is often absent in adults. Consider it when cough is paroxysmal, causes post-tussive vomiting, or has persisted for weeks — especially with sick contacts.

Multiple etiologies are common: Up to 25% of chronic cough patients have more than one contributing cause. Partial response to treatment suggests additional factors — continue working treatments while adding therapy for other suspected causes.

Critical Pitfalls to Avoid

Stopping ACE inhibitors too briefly: Cough may take 1-4 weeks to resolve after stopping, and occasionally up to 3 months. Do not conclude the ACE inhibitor was not the cause after only a few days. Give it adequate time before resuming evaluation.

Prescribing antibiotics for acute bronchitis: Acute bronchitis is almost always viral. Antibiotics provide no benefit and contribute to antibiotic resistance. Resist patient pressure for unnecessary antibiotics — educate about expected duration and symptomatic treatment.

Inadequate treatment duration: Inhaled corticosteroids for asthma require 6-8 weeks to assess efficacy. Proton pump inhibitors for reflux-related cough require 2-3 months of twice-daily dosing. Abandoning treatment too early leads to missed diagnoses.

Dismissing cough in a smoker as “just smoker’s cough”: New or changed cough in a smoker over age 40 is lung cancer until proven otherwise. Always obtain a chest radiograph, and have a low threshold for chest CT. Early detection saves lives.

Ignoring red flags: Hemoptysis, weight loss, night sweats, and progressive dyspnea demand urgent investigation. Do not attribute these to benign causes without thorough evaluation. Missing lung cancer or tuberculosis has devastating consequences.

Ruling out gastroesophageal reflux disease because “there’s no heartburn”: Silent reflux without typical symptoms accounts for the majority of reflux-related cough. Always include gastroesophageal reflux disease in your differential for chronic cough, even when the patient denies classic symptoms.

Assuming normal examination excludes serious disease: Many causes of chronic cough — including asthma, gastroesophageal reflux disease, upper airway cough syndrome, and ACE inhibitor-induced cough — have completely normal physical examinations. A normal exam does not provide reassurance.

Using once-daily proton pump inhibitor for suspected reflux-cough: Standard once-daily proton pump inhibitor is insufficient for reflux-related cough. Twice-daily dosing (before breakfast and before dinner) for at least 2-3 months is required for an adequate therapeutic trial.

Key Takeaways

Duration classifies cough: Acute (less than 3 weeks), subacute (3-8 weeks), and chronic (greater than 8 weeks) have fundamentally different etiologies and approaches. Establish duration first.
“The Big Three” cause 90% of chronic cough: In non-smoking adults with a normal chest radiograph, upper airway cough syndrome, asthma, and gastroesophageal reflux disease account for the vast majority of cases.
Multiple causes are common: Up to 25% of patients have more than one etiology. Partial response to treatment indicates additional contributing factors that must be addressed.
Empiric treatment is both diagnostic and therapeutic: Response to specific therapy confirms the diagnosis. Ensure adequate duration before concluding treatment failure.
Check medications first: ACE inhibitors cause cough in 5-20% of patients. This is easily treatable by switching to an ARB. Always ask about blood pressure medications by name.
Silent reflux is the rule, not the exception: Up to 75% of reflux-related cough occurs without heartburn. Do not exclude gastroesophageal reflux disease based on absence of typical symptoms.
Red flags require urgent action: Hemoptysis, weight loss, night sweats, progressive dyspnea, hoarseness greater than 3 weeks, and new cough in smokers over 40 demand expedited evaluation.
Normal examination is common and not reassuring: Many of the most common causes of chronic cough have completely normal physical examination findings.
Acute bronchitis does not need antibiotics: Resist pressure to prescribe. Educate patients about the viral etiology and expected 2-3 week duration of cough.
Consider pertussis in prolonged cough: The “100-day cough” is frequently missed in adults. Consider testing when cough is paroxysmal or persists beyond 2-3 weeks.

Quick Reference Algorithm

Systematic Approach to Cough:

Assess urgency: Are there red flags requiring immediate action? (Hemoptysis, severe dyspnea, hypoxia, suspected pulmonary embolism or pneumonia)
Establish duration: Acute (less than 3 weeks), subacute (3-8 weeks), or chronic (greater than 8 weeks)?
For chronic cough — check these first:
- Is the patient on an ACE inhibitor? → Stop and switch to ARB
- Is the patient a current smoker? → Chest radiograph; smoking cessation; consider cancer screening
- Is the chest radiograph abnormal? → Pursue specific diagnosis
Evaluate for “The Big Three”: Upper airway cough syndrome, asthma, gastroesophageal reflux disease — consider empiric treatment trials
Ensure adequate treatment duration: 2-3 weeks for antihistamines; 6-8 weeks for inhaled corticosteroids; 2-3 months for proton pump inhibitors
Consider multiple etiologies: If partial response, continue effective treatments while adding therapy for other suspected causes
Refer if refractory: Specialist evaluation for cough not responding to systematic approach after 2-3 months