Chronic cough differential diagnosis

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Cough protects the airway. Acute viral epithelial irritation can persist for weeks, but daily cough beyond expected recovery may signal retained secretion, ongoing inflammation, aspiration or a hypersensitive reflex.

Wet quality directs attention to endobronchial secretions. Protracted bacterial bronchitis, bronchiectasis, CF, ciliary disease, foreign body and aspiration form a linked spectrum that requires active differentiation.

Dry cough can reflect post-viral hypersensitivity, asthma, upper-airway irritation, environmental exposure or a tic. Timing alone rarely identifies the cause.

History begins at the first day, not the clinic date. Abrupt onset is a foreign-body clue; neonatal onset suggests congenital or aspiration disease; repetitive paroxysms suggest pertussis.

Examination includes growth, oxygenation, clubbing, ENT, chest symmetry and crackles, cardiac signs and neurodevelopment. Observe swallowing when feeds trigger cough.

Chest radiography detects focal collapse, consolidation and gross structural change but early bronchiectasis and radiolucent objects can be invisible.

Spirometry assesses obstruction and reversibility. Normal results do not exclude intermittent asthma, but repeated normal objective testing weakens an asthma explanation for isolated cough.

PBB is a clinical treatment-response diagnosis. Antibiotic choice covers common airway bacteria; incomplete response requires confirmation of dose and adherence and a broader disease search.

CT uses child-optimised protocols only when structural information will change care. Bronchoscopy retrieves foreign bodies, samples lower-airway organisms and evaluates anatomy in selected cases.

Reassurance is an active outcome after a normal assessment: explain expected duration, remove irritants, avoid suppressants and set a date for reassessment.

Families can experience substantial sleep and school disruption even when physiology is safe. Validate burden while avoiding unsupported medicine trials.

Multidisciplinary care may include respiratory, ENT, speech and language therapy, immunology, physiotherapy and psychology according to the cough pathway.

Key points

Definitions vary: paediatric respiratory pathways commonly investigate daily cough beyond 4 weeks, while traditional BTS terminology calls more than 8 weeks chronic. Use trajectory and red flags rather than waiting for a label.
First branch is wet versus dry. A wet cough indicates airway secretion even when a child swallows sputum; parent-recorded audio or video can improve description.
First-line assessment is detailed history, examination, chest radiograph and spirometry with bronchodilator response when age and ability permit.
Ask onset, choking, cough-free intervals, nights, exercise, meals, position, triggers, whoop, vomiting, infections, medicines, smoke or vaping, travel and family history.
A normal chest radiograph does not exclude foreign body, bronchiectasis or aspiration. Red flags determine specialist CT, bronchoscopy, sweat test, ciliary, immune or swallow testing.
Protracted bacterial bronchitis is an isolated chronic wet cough without alternative pointers that resolves after an appropriate 2-week antibiotic, usually co-amoxiclav. Obtain culture when feasible and review at the end.
If wet cough fails to resolve after 2–4 weeks of appropriate treatment or recurs repeatedly, investigate bronchiectasis, foreign body, immune deficiency, CF and primary ciliary dyskinesia rather than repeating courses indefinitely.
Asthma causes variable wheeze, breathlessness, triggers and objective airflow or inflammatory evidence. Isolated dry cough without these features should not receive escalating inhaled corticosteroid indefinitely.
Post-infectious cough gradually improves after viral illness or pertussis. Antibiotics do not shorten a recovering viral cough; pertussis treatment mainly reduces transmission within its window.
Somatic or tic cough is diagnosed positively after organic red flags are excluded; characteristic distractibility, suppressibility or absent sleep cough can support it. Avoid dismissive language.
Do not empirically treat gastro-oesophageal reflux without compatible regurgitation, pain, dysphagia or aspiration features; acid suppression can cause harm.
Remove smoke and vape exposure, check vaccination and provide a defined follow-up endpoint. Worsening breathing, haemoptysis, fever, weight loss or reduced intake needs earlier review.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Persistent airway infection

Protracted bacterial bronchitis and bronchiectasis retain infected secretions that stimulate a daily wet cough. within the child-specific clinical phenotype.

Variable airway inflammation

Asthma and eosinophilic disease produce episodic dry cough with wheeze, triggers and reversible airflow change. within the child-specific clinical phenotype.

Mechanical or aspiration cause

Foreign body, swallowing dysfunction, airway malacia and congenital lesions repeatedly irritate or obstruct the airway. within the child-specific clinical phenotype.

Post-infectious neural sensitivity

Viral or pertussis injury can leave a hypersensitive cough reflex after active infection has resolved. within the child-specific clinical phenotype.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Secretion receptor stimulation
Mucus and neutrophilic inflammation activate airway sensory nerves and produce the audible wet cough phenotype. during progression of the respiratory disorder.
2
Bronchial hyperresponsiveness
Inflamed asthmatic airways constrict to triggers, creating variable obstruction, wheeze and cough. during progression of the respiratory disorder.
3
Repeated aspiration injury
Food, liquid or refluxate entering the airway causes chemical inflammation, infection and progressive structural damage. during progression of the respiratory disorder.
4
Cough hypersensitivity and learning
After illness, heightened sensory gain and tic reinforcement can sustain cough without ongoing lower-airway disease. during progression of the respiratory disorder.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Cough quality

Clarify wet, dry, barking, paroxysmal or honking sound using caregiver recordings when clinic cough is absent.

Onset and timing

Establish abrupt choking, neonatal onset, infection, nights, exercise, meals, position and cough-free periods.

Associated respiratory features

Ask wheeze, stridor, breathlessness, sputum, haemoptysis, fever and recurrent focal pneumonia.

Systemic and growth features

Plot growth and assess stool, clubbing, ENT disease, immune infections, night sweats and development.

Exposure

Review smoke, vaping, damp, pets, allergens, TB contact, travel, vaccination and cough-inducing medicines.

Functional pattern

Assess sleep, school and suppressibility while avoiding an early psychogenic label before organic assessment.

Red flags requiring action

Daily wet cough is abnormal and suggests endobronchial infection, bronchiectasis, aspiration or impaired clearance.
Sudden onset after choking, unilateral wheeze or recurrent same-lobe pneumonia requires foreign-body assessment even with normal radiography.
Clubbing, faltering growth, hypoxaemia, haemoptysis, recurrent pneumonia or abnormal chest signs requires paediatric respiratory referral.
Neonatal onset, feeding difficulty, cough with meals or recurrent aspiration suggests congenital, ciliary or swallowing disease.
TB contact, travel, weight loss, fever or night sweats requires prompt specialist and public-health investigation.
Progressive breathlessness, exercise limitation, cardiac signs, immune deficiency or abnormal spirometry prevents a nonspecific-cough label.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
First-line: chest radiographFirst stepFirst line
Why
Identify focal collapse, infection, gross structural disease or cardiac enlargement.
Interpretation and limitations
A normal film narrows but does not exclude foreign body, aspiration or bronchiectasis.
02
First-line when able: spirometry with reversibilityFirst line
Why
Assess obstructive physiology and variable bronchodilator response.
Interpretation and limitations
Reversibility supports asthma in the correct phenotype; normal testing weakens but may not exclude intermittent disease.
03
Airway culture
Why
Identify bacteria in chronic wet cough or exacerbation before antibiotics when possible.
Interpretation and limitations
Interpret sputum, cough swab or lavage quality and repeated organisms with the respiratory team.
04
Thin-section CT
Why
Confirm bronchiectasis or define persistent focal structural disease.
Interpretation and limitations
Use specialist, child-optimised imaging when wet cough, clubbing, abnormal film or treatment failure justifies radiation.
05
Directed bronchoscopy, CF, ciliary, immune or swallow tests
Why
Investigate specific red flags and treatable causes.
Interpretation and limitations
Sudden focal disease prioritises bronchoscopy; multisystem and feeding phenotypes determine other specialist tests.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Protracted bacterial bronchitis

Chronic isolated wet cough resolving after appropriate 2-week antibiotic supports PBB, with recurrence prompting further investigation.

Asthma

Variable wheeze, breathlessness, night or exercise triggers and objective reversibility support asthma over isolated cough. when timing, examination and trajectory are integrated.

Bronchiectasis or cystic fibrosis

Clubbing, poor growth, recurrent infection, abnormal cultures or persistent wet cough directs CT and CF evaluation.

Foreign body or aspiration

Abrupt onset, focal signs or feeding association requires bronchoscopy or swallowing assessment despite normal routine imaging.

Post-infectious, tic or upper-airway cough

Gradual improvement, characteristic suppressibility or prominent rhinitis can support these after lower-airway red flags are excluded.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01TriageSeparate wet, dry and dangerousFirst stepCough persists daily beyond expected acute recovery.

1Identify physiological instability and red flags and establish wet versus dry quality.
2Take onset, trigger, feeding, infection and exposure history and examine growth, clubbing and focal signs.
3Obtain chest radiography and spirometry when feasible, then select rather than scatter further tests.

02WetTreat PBB only when phenotype fitsIsolated daily wet cough persists without another specific pointer.

1Send airway culture where feasible and give an appropriate 2-week co-amoxiclav course using current BNF-C dosing.
2Review for complete resolution and confirm adherence and dose.
3Investigate bronchiectasis and causes if cough persists after 2–4 weeks or recurs repeatedly.

03DrySeek objective variable diseasePersistent cough is dry without suppurative red flags.

1Assess wheeze, triggers, atopy, rhinitis, post-infectious trajectory, smoke and cough-inducing medicine.
2Use FeNO and spirometry through the asthma algorithm when the phenotype is compatible.
3Avoid indefinite empirical ICS, antibiotic or acid suppression when objective response and features are absent.

04SpecificRefer from the red flagChoking, focal signs, clubbing, growth failure, haemoptysis or feeding association is present.

1Use urgent bronchoscopy for high foreign-body suspicion and respiratory CT for suspected bronchiectasis.
2Use sweat, ciliary, immune, TB or swallow testing according to the specific phenotype.
3Treat the cause through the specialist team and monitor functional and structural recovery.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Missed progressive lung disease

Labelling wet cough as benign delays diagnosis of bronchiectasis, CF, aspiration or retained foreign body. when recognition or effective treatment is delayed.

Structural airway injury

Ongoing infection and aspiration can produce irreversible bronchial dilatation, fibrosis and impaired lung growth. when recognition or effective treatment is delayed.

Medicine-related harm

Repeated antibiotics, corticosteroids and acid suppression cause adverse effects and diagnostic anchoring without a compatible phenotype.

Functional and family impact

Persistent cough disrupts sleep, school, exercise and relationships and can reinforce anxiety or tic behaviour. when recognition or effective treatment is delayed.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Define the expected endpoint and review date for every treatment trial.
Document whether wet cough resolves completely, partially or recurs after antibiotic.
Track growth, activity, sleep, school and oxygenation alongside cough frequency.
Reassess new fever, haemoptysis, weight loss, focal signs or breathlessness urgently.
Review inhaler technique and objective asthma evidence before stepping up ICS.
Reduce smoke and vape exposure with household support, not blame.
Refer recurrent or unexplained cough rather than cycling through empirical medicines.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Children swallow sputum

A caregiver's wet-cough description is clinically meaningful even when no sputum sample is produced.

Four weeks prompts thought

Investigation should begin earlier when red flags exist and should not be postponed simply to reach an 8-week label.

PBB requires complete response

Partial improvement is not diagnostic and should reopen adherence, organism, bronchiectasis and aspiration assessment.

Normal radiography has limits

Radiolucent foreign body and early bronchiectasis can remain invisible despite clinically important disease.

A therapeutic trial is an experiment

State the hypothesis, duration and measurable response and stop treatment when the predicted result does not occur.

11Common pitfallsFrequent interpretation and management errors.

01
Do not call a daily wet cough normal.
02
Do not wait 8 weeks when a foreign body or serious red flag is present.
03
Do not exclude foreign body or bronchiectasis from a normal radiograph.
04
Do not diagnose asthma from isolated cough without compatible variability.
05
Do not repeat antibiotics indefinitely for recurrent wet cough.
06
Do not prescribe acid suppression without reflux-related features.
07
Do not label cough psychogenic before positive assessment and red-flag exclusion.
08
Do not end follow-up without a defined recovery or escalation point.