What causes incessant coughing?

Causes of Incessant Coughing

The most common causes of incessant (chronic) coughing are upper airway cough syndrome (UACS), asthma including cough-variant asthma, gastroesophageal reflux disease (GERD), and nonasthmatic eosinophilic bronchitis (NAEB), which together account for over 90% of cases in nonsmokers with normal chest radiographs who are not taking ACE inhibitors. 1

Primary Etiologies

The "Big Four" Causes

• Upper Airway Cough Syndrome (UACS): Previously called postnasal drip syndrome, this represents irritation from nasal secretions reaching the larynx, often linked to rhinitis or sinusitis 2, 1

• Asthma/Cough-Variant Asthma: Can present with cough as the only symptom without wheezing or breathlessness—these patients have bronchial hyperresponsiveness but a higher wheezing threshold 1, 3

• Gastroesophageal Reflux Disease (GERD): Critically, GERD can be "silent" from a GI standpoint in up to 75% of chronic cough cases, meaning patients have no heartburn or regurgitation 2, 1

• Nonasthmatic Eosinophilic Bronchitis (NAEB): Characterized by eosinophilic airway inflammation with normal spirometry and no bronchial hyperresponsiveness—often missed if not specifically considered 1

Additional Common Causes

• ACE Inhibitor Medications: A well-established cause that may take months to resolve after discontinuation 2

• Chronic Bronchitis/COPD: Typically associated with smoking history and usually accompanied by sputum production 2

• Pertussis Infection: Increasingly recognized as causing persistent cough; 10% of chronic cough cases in one series had positive nasal swabs for Bordetella 2

• Bronchiectasis: Can present as "dry" bronchiectasis without sputum production, though this accounts for only about 4% of specialist cough clinic cases 2

• Lung Cancer: The fourth most common presenting feature of lung cancer, particularly important in smokers 2

Pediatric-Specific Causes

In children, the etiology differs somewhat:

• Respiratory infections and post-infectious cough: Recurrent URTIs, pertussis, and Mycoplasma can cause prolonged cough 2

• Protracted bacterial bronchitis: A common cause in children 6-14 years 4

• Airway lesions: Congenital tracheomalacia or vascular anomalies—75% of affected children present with persistent cough 2

• Foreign body aspiration: Cough is present in up to 70% of cases in some series 2

• GERD is rarely the sole cause in children with isolated chronic cough, unlike in adults 2

Critical Diagnostic Pitfalls

Character and Timing Are Not Diagnostically Helpful

• The character of cough (wet, dry, paroxysmal, barking) does not predict the underlying cause 2, 1

• The timing of cough (nocturnal, with meals, postural) is similarly non-diagnostic 2, 1

• This is a crucial point: clinicians cannot rely on cough characteristics to guide diagnosis and must systematically evaluate for the common causes 1

Absence of Classic Symptoms Does Not Rule Out Diagnosis

• Absence of heartburn does not exclude GERD as the cause 2, 1

• Absence of wheezing does not exclude asthma 1, 3

• Absence of nasal symptoms does not exclude UACS 2

• Each of these conditions can present with cough as the sole manifestation 1

Multiple Simultaneous Causes Are Common

• Many patients have more than one reason for chronic cough occurring simultaneously 5

• Treatment must address all contributing factors for resolution 5, 6

Environmental and Occupational Triggers

• Cigarette smoke exposure (active or passive) is a major cause 2, 6

• Occupational sensitizers: Hot acidic conditions, chemical exposures, and dust can cause persistent cough 2

• Environmental pollutants and particulates contribute to chronic cough in the community 6

Less Common But Important Causes

• Medications beyond ACE inhibitors: Interferon alpha, certain antiretroviral therapies 2

• Atopic disease: Increases respiratory symptoms including cough 2

• Psychogenic/habit cough: Particularly in children, though this is a diagnosis of exclusion 2

• Arnold ear-cough reflex: Rare (2.3-4.2% of people) but can be triggered by ear canal stimulation from wax or other pathology 2

Underlying Mechanism: Cough Hypersensitivity

• Chronic cough is fundamentally characterized by persistent upregulation of the cough reflex 7, 6

• The associated conditions (UACS, asthma, GERD, NAEB) may act as triggers rather than fundamental causes, driving sensitization of cough pathways 7

• This explains why cough can persist even after treating the apparent underlying condition and why some cases remain refractory 7, 5