Differential Diagnosis for Persistent Dry Cough Three Months Post-Viral Bronchitis
At three months post-viral bronchitis, this patient's persistent dry cough has transitioned from subacute to chronic cough, and you must systematically evaluate for upper airway cough syndrome (previously postnasal drip), asthma, gastroesophageal reflux disease, and nonasthmatic eosinophilic bronchitis—the four conditions that account for the vast majority of chronic cough cases. 1, 2
Key Temporal Classification
- This is now chronic cough (>8 weeks duration), not postinfectious cough, which by definition resolves within 8 weeks of the initial respiratory infection 1, 3
- The ACCP guidelines explicitly state that if cough persists beyond 8 weeks following acute respiratory infection, you must consider diagnoses other than postinfectious cough 1
Primary Differential Diagnoses to Evaluate
1. Upper Airway Cough Syndrome (UACS)
- Most common cause of chronic cough, accounting for approximately 60% of cases in clinical series 4
- Pathogenesis involves persistent inflammation of nose and paranasal sinuses following the viral infection 1
- Look for: throat clearing, sensation of postnasal drip, nasal discharge, or rhinosinusitis symptoms 1, 5
2. Asthma (Including Cough-Variant Asthma)
- Critical not to miss, as asthma is commonly misdiagnosed as acute bronchitis in approximately one-third of patients presenting with acute cough 1, 6
- Approximately 40% of previously healthy individuals develop transient bronchial hyperresponsiveness after acute respiratory infections, though this typically resolves within 6 weeks 6
- In retrospective studies, 65% of patients with recurrent "acute bronchitis" episodes actually had mild asthma 1
- Accounts for 26-58% of chronic cough cases 4, 5
- Look for: wheezing, dyspnea, nocturnal symptoms, or response to bronchodilators 2
3. Gastroesophageal Reflux Disease (GERD)
- Accounts for 9-41% of chronic cough cases 4, 5
- May be triggered or exacerbated by vigorous coughing from the initial viral illness 1
- The "pathogenic triad" of asthma, UACS, and GERD accounts for 93.6% of chronic cough cases 5
- Look for: heartburn, regurgitation, or cough worsening after meals or when supine 2
4. Nonasthmatic Eosinophilic Bronchitis
- Important cause when spirometry is normal but cough persists 2
- Requires sputum eosinophil analysis for diagnosis 2
Less Common but Important Considerations
Bordetella Pertussis Infection
- Must consider if: paroxysms of coughing, post-tussive vomiting, or inspiratory whooping sound are present 1
- Diagnosis should be made when cough lasts >2 weeks with these characteristic features unless another diagnosis is proven 1
Other Considerations
- Bronchiectasis: accounts for 5-17.9% of chronic cough cases 4, 5
- Chronic obstructive pulmonary disease: especially if smoking history 1, 2
- Medication-induced: rule out ACE inhibitor use 2
Diagnostic Approach
Initial Evaluation
- Chest radiograph is essential to rule out pneumonia, malignancy, or other structural abnormalities 1, 7
- Spirometry to evaluate for asthma or obstructive lung disease 1, 2
- Clinical assessment for UACS symptoms (rhinosinusitis, postnasal drip) 1
Targeted Investigations if Initial Workup Unrevealing
- CT of paranasal sinuses if UACS suspected 5
- Bronchial provocation testing (methacholine or carbachol) for asthma 5
- 24-hour esophageal pH monitoring for GERD 5
- Sputum eosinophil count for nonasthmatic eosinophilic bronchitis 2
Critical Pitfalls to Avoid
- Do not assume this is still "postinfectious cough" at 3 months duration—this diagnosis is only valid for 3-8 weeks post-infection 1, 3
- Do not prescribe antibiotics unless bacterial sinusitis or pertussis is specifically suspected, as viral etiology accounts for >90% of initial bronchitis cases 1, 8
- Do not overlook extrapulmonary causes, particularly UACS and GERD, which are frequently missed in non-specialized settings 4
- Do not miss underlying asthma, which is the most commonly overlooked diagnosis in patients with recurrent "bronchitis" 1, 6