What is the cause of a medical condition?

Common Causes of Medical Conditions

The three most common causes of chronic cough are upper airway cough syndrome (UACS), asthma, and gastroesophageal reflux disease (GERD), which together account for 92-100% of cases in nonsmokers with normal chest radiographs who are not taking ACE inhibitors. 1

Primary Causes of Chronic Cough

Most Common Causes

1. Upper Airway Cough Syndrome (UACS)

   • Previously known as post-nasal drip syndrome (PNDS)
   • Can present as "silent UACS" with cough as the only symptom
   • Caused by various rhinosinus conditions

2. Asthma

   • May present as "cough variant asthma" with cough as the primary symptom
   • No other typical asthma symptoms may be present

3. Gastroesophageal Reflux Disease (GERD)

   • Can manifest as "silent GERD" with cough but no typical reflux symptoms
   • Diagnosis often requires empiric treatment or specialized testing

Less Common but Important Cause

1. Nonasthmatic Eosinophilic Bronchitis (NAEB)
   • Characterized by cough, eosinophilic infiltration, normal spirometry
   • Prevalence ranges from 13-33% in studies outside the United States
   • Can be diagnosed by properly performed staining of induced sputum for eosinophils
   • Responds predictably to inhaled corticosteroid therapy

Uncommon Causes of Cough

When common causes have been ruled out, consider uncommon causes, which include:

Pulmonary Disorders

• Tracheobronchomalacia
• Airway stenosis/strictures
• Tracheobronchial amyloidosis
• Airway foreign bodies
• Pulmonary edema
• Pulmonary embolism

Nonpulmonary Disorders

• Connective tissue disorders (rheumatoid arthritis, lupus, etc.)
• Vasculitides (Wegener's granulomatosis, giant cell arteritis)
• Esophageal disorders
• Inflammatory bowel diseases
• Thyroid disorders

Diagnostic Approach

When evaluating a patient with chronic cough:

1. Rule out common triggers first:

   • ACE inhibitor use
   • Smoking
   • Abnormal chest radiograph findings

2. Systematically evaluate for the triad of common causes:

   • UACS
   • Asthma
   • GERD

3. Consider NAEB if initial evaluations are negative, particularly by testing for sputum eosinophilia

4. Only after thorough evaluation for common causes, consider uncommon causes 1

Important Clinical Considerations

• The character, timing, or presence of sputum production in cough has limited diagnostic value
• Even with significant bronchorrhea, the common triad causes are still most likely
• Medical history is important for identifying ACE inhibitor use, smoking status, geographic exposures (TB, fungal diseases), and history of cancer or immunocompromise
• Uncommon causes should only be considered when evaluation for common causes has been thorough and unsuccessful 1

Conclusion

When determining the cause of a medical condition, particularly chronic cough, a systematic approach focusing first on the most common etiologies will yield the highest diagnostic success. The evidence clearly demonstrates that for chronic cough, UACS, asthma, and GERD represent the overwhelming majority of cases, and should be the initial focus of diagnostic evaluation.