Causes of Chronic Cough
In patients with chronic cough (lasting >8 weeks), the three dominant causes account for 92-100% of cases in nonsmokers not taking ACE inhibitors with normal chest X-rays: Upper Airway Cough Syndrome (UACS, formerly post-nasal drip syndrome), asthma, and gastroesophageal reflux disease (GERD)—either alone or in combination. 1
The "Big Three" Etiologies
The evidence from ACCP guidelines demonstrates remarkable consistency across multiple prospective studies from different countries 1:
- Upper Airway Cough Syndrome (UACS): Due to various rhinosinus conditions
- Asthma: Including "cough variant asthma" where cough is the only symptom
- Gastroesophageal Reflux Disease (GERD): Including "silent GERD" without typical reflux symptoms
These three conditions are so ubiquitous that in Western Hemisphere studies, they explained chronic cough in 92-100% of nonsmoking patients not on ACE inhibitors with normal chest radiographs 1. Critically, each can present with cough as the ONLY symptom—no other clinical findings may be present.
Initial Exclusions (Must Rule Out First)
Before pursuing the "big three," two common iatrogenic/behavioral causes must be addressed:
- Current cigarette smoking: Stop smoking and wait 4-6 weeks 2
- ACE inhibitor use: Discontinue and wait 4-6 weeks for resolution 1
Less Common But Important Causes
Nonasthmatic Eosinophilic Bronchitis (NAEB) deserves early consideration despite being less common 1:
- Prevalence: 13-33% in non-US studies, though oddly absent in many US series
- Characterized by: cough, eosinophilic bronchial infiltration, normal spirometry, no bronchial hyperresponsiveness
- Key advantage: Relatively easy to diagnose via induced sputum eosinophil staining and predictably responds to inhaled corticosteroids
Other less frequent causes include 1:
- Chronic bronchitis/COPD (in smokers)
- Postinfectious cough (including pertussis in localized outbreaks)
- Bronchiectasis
- Obstructive sleep apnea (more common in men) 3
- Medications beyond ACE inhibitors
- Endobronchial abnormalities (tumors, tuberculosis, sarcoidosis)
- Interstitial lung disease
- Psychogenic/habitual cough
Critical Clinical Pitfalls
The cough characteristics themselves are diagnostically worthless 1. The character, timing, or presence/absence of sputum production does not help identify the cause. Even significant sputum production in a nonsmoker not on ACE inhibitors with normal chest X-ray will usually be due to UACS, asthma, or GERD.
However, the medical history IS valuable for:
- ACE inhibitor use
- Smoking status (current or former)
- Geographic exposure to tuberculosis or endemic fungi
- Previous history of cancer, tuberculosis, or AIDS
- Systemic symptoms: fever, night sweats, weight loss (red flags requiring urgent evaluation)
Recommended Diagnostic Approach
The ACCP guidelines recommend focusing diagnostic efforts on detecting UACS, asthma, NAEB, or GERD—alone or in combination—as this approach yields the highest success rate 1. This focused strategy is far more productive than routinely searching for rare or obscure diagnoses.
Initial cost-effective testing should include 4:
- Chest radiography
- Spirometry
- Assessment of medications and environmental/occupational triggers
Multiple causes frequently coexist—one, two, or all three of the dominant etiologies may be present simultaneously 1.
When Cough Persists Despite Treatment
If cough remains refractory after thorough evaluation and optimal treatment of identified causes, consider cough hypersensitivity syndrome (also called refractory chronic cough) 5, 2. This involves neuronal dysregulation with peripheral and central mechanisms, characterized by throat tickle/itch and cough triggered by innocuous stimuli. Treatment options include speech therapy, gabapentin, or amitriptyline 5, 4.
Gender Considerations
Recent evidence shows men have higher rates of UACS (75% vs 53%) and OSA (21% vs 6%) compared to women, and men show greater treatment response (median VAS reduction 32mm vs 17.5mm) 3, suggesting gender-specific evaluation may be warranted.