What is the approach to diagnosing a chronic cough?

Diagnosing Chronic Cough

The diagnostic approach to chronic cough (lasting >8 weeks) should focus primarily on detecting and treating the three most common causes: Upper Airway Cough Syndrome (UACS), asthma, and Gastroesophageal Reflux Disease (GERD), as these account for the vast majority of cases in non-smokers with normal chest X-rays. 1

Initial Evaluation

1. Define chronicity: Confirm cough duration >8 weeks 1, 2

2. Rule out red flags requiring urgent attention:

   • Fever, weight loss, hemoptysis, recurrent pneumonia 2
   • History of cancer, tuberculosis, or immunocompromise 1

3. Essential first-line investigations:

   • Chest radiograph (mandatory) 1, 2
   • Medication review (especially ACE inhibitors) 1
   • Smoking status assessment 1

4. Key history elements to assess:

   • Timing and pattern of cough (worsening after meals suggests GERD) 1
   • Productive vs. non-productive nature 1
   • Environmental/occupational exposures 1
   • Associated symptoms (postnasal drip, heartburn, wheezing) 1

Systematic Approach to Common Causes

1. Medication and Environmental Causes

• ACE inhibitors: Discontinue regardless of temporal relationship to cough onset (resolution typically within days to 2 weeks) 1
• Smoking: Recommend cessation (cough typically resolves within 4 weeks) 1
• Environmental irritants: Identify and eliminate exposure 1

2. Upper Airway Cough Syndrome (UACS)

• Clinical features: Postnasal drip, throat clearing, nasal discharge 1
• Diagnostic approach:
  • Trial of first-generation antihistamine/decongestant for 2-4 weeks 1
  • Consider nasal endoscopy or CT of paranasal sinuses if symptoms persist 3

3. Asthma and Related Conditions

• Clinical features: May present only as cough without wheezing ("cough variant asthma") 4
• Diagnostic approach:
  • Spirometry (essential) 1
  • Consider peak flow measurements 1
  • Fractional exhaled nitric oxide (FeNO) testing 1
  • Bronchial provocation testing if spirometry normal 1
  • Consider induced sputum analysis for eosinophils (for non-asthmatic eosinophilic bronchitis) 1

4. Gastroesophageal Reflux Disease (GERD)

• Clinical features: May be "silent" with no typical reflux symptoms 4, 1
• Predictive profile: Non-smoker, not taking ACE inhibitors, normal chest X-ray, cough worsening after meals 1
• Diagnostic approach:
  • Empiric trial of PPI therapy (twice-daily for 3 months) 1
  • Consider 24-hour esophageal pH monitoring if symptoms persist 1
  • Note: Normal esophagoscopy does not rule out GERD-related cough 1

Additional Testing for Persistent Cough

If initial evaluation and empiric treatment for common causes fail:

1. Advanced imaging: High-resolution CT scan of the chest 1, 2

2. Specialized testing:

   • Laryngoscopy for hoarseness 3
   • Bronchoscopy for persistent unexplained cough 1
   • Sputum evaluation for suspected infection or inflammatory response 1

3. Consider less common causes:

   • Bronchiectasis
   • Chronic bronchitis
   • Interstitial lung disease
   • Congestive heart failure
   • Thyroid disease
   • Neuromuscular disorders
   • Mediastinal mass 4

Refractory Chronic Cough

For persistent cough despite thorough evaluation:

• Consider cough hypersensitivity syndrome 2
• Treatment options include neuromodulators (gabapentin, pregabalin) and speech pathology therapy for cough suppression techniques 1, 2

Follow-up and Re-evaluation

• Re-evaluate if cough persists beyond 4-6 weeks of appropriate treatment 1
• Consider specialist referral if:
  • Cough persists despite appropriate treatment
  • Suspected serious underlying pathology
  • Significant impact on quality of life 1

Common Pitfalls to Avoid

• Failing to discontinue ACE inhibitors 1
• Not considering "silent" GERD as a cause for cough 4, 1
• Inadequate duration of treatment, especially for GERD 1
• Using cough character or timing alone to rule in/out specific diagnoses 4
• Overlooking multiple concurrent causes (up to 25% of cases) 5