What is the appropriate evaluation and treatment for a patient with a persistent cough lasting 1 month?

Evaluation and Management of Cough Lasting 1 Month

For a patient with cough lasting 1 month (subacute cough), first determine if this is postinfectious cough following a recent respiratory infection, then treat empirically for the most common causes: upper airway cough syndrome (postnasal drip), transient bronchial hyperresponsiveness, or early gastroesophageal reflux disease. 1

Initial Classification and Red Flag Assessment

A cough lasting 1 month falls into the subacute category (3-8 weeks duration) and requires a different approach than acute or chronic cough 1, 2:

• Screen immediately for red flags: hemoptysis, significant unintentional weight loss, voice changes, fever, or night sweats that would suggest serious underlying disease requiring urgent investigation 2
• Review medications: Stop ACE inhibitors if the patient is taking one, as these commonly cause persistent cough 1, 2
• Assess smoking status: Current smoking has a dose-related association with persistent cough and should prompt cessation counseling 1, 2

Diagnostic Approach

Baseline Investigations

Obtain a chest radiograph in all patients with subacute cough to rule out pneumonia, malignancy, or other serious thoracic pathology before proceeding with empiric treatment 1. The chest radiograph should be normal or near-normal before using a diagnostic algorithm for common causes 1.

Determine if Postinfectious

The critical first step is determining whether this is postinfectious cough (following a recent upper respiratory infection) versus other causes 1, 2:

• Postinfectious cough is defined as cough persisting for 3-8 weeks after symptoms of acute respiratory infection 1, 2
• Multiple mechanisms contribute: postviral airway inflammation (48.4%), upper airway cough syndrome (33.2%), cough-variant asthma (15.8%), and nonasthmatic eosinophilic bronchitis (5.4%) 2

Special Consideration: Pertussis

Suspect pertussis if the cough has lasted ≥2 weeks and is accompanied by paroxysms of coughing, post-tussive vomiting, or inspiratory whooping sound 1, 2:

• Obtain nasopharyngeal aspirate or swab for culture confirmation 1
• If pertussis is confirmed, treat with macrolide antibiotics and isolate for 5 days from treatment start 3
• Pertussis is frequently underdiagnosed in adults 2

Treatment Algorithm for Subacute Cough

If Postinfectious Cough is Confirmed

Start with inhaled ipratropium bromide as first-line therapy, as it may attenuate postinfectious cough 1, 3:

1. First-line: Inhaled ipratropium 1, 3

2. If inadequate response: Add inhaled corticosteroids when cough adversely affects quality of life 1

3. For severe paroxysms: Consider prednisone 30-40 mg daily for a short, finite period after ruling out other common causes (upper airway cough syndrome, asthma, GERD) 1, 3

4. If other measures fail: Central acting antitussives like dextromethorphan (60 mg for optimal suppression, not standard OTC doses) or sedating antihistamines for nighttime cough 1, 3

Important: Antibiotics have no role in postinfectious cough unless bacterial sinusitis or early pertussis is confirmed 1

If Non-Postinfectious or Unclear Etiology

Treat empirically in sequential and additive steps for the most common causes, as more than one may be present simultaneously 1:

1. Start with upper airway cough syndrome (postnasal drip): First-generation antihistamine/decongestant combination 1, 4

2. If cough persists, add asthma treatment: Even without wheezing, consider empiric trial of inhaled bronchodilators and corticosteroids 1, 4

3. If still persistent, add GERD treatment: Empiric proton pump inhibitor therapy without testing 1, 4

Symptomatic Relief Options

For benign viral cough requiring symptomatic relief 3:

• Simple home remedies first: Honey and lemon may be as effective as pharmacological treatments 3
• Dextromethorphan: Use 60 mg (not standard OTC doses of 15-30 mg which are subtherapeutic) for maximum cough reflex suppression 3
• Menthol inhalation: Provides acute but short-lived relief 3
• First-generation antihistamines: Particularly suitable for nocturnal cough, though they cause drowsiness 3
• Avoid codeine: No greater efficacy than dextromethorphan but significantly more adverse effects 3

Follow-Up and Reassessment

Reassess within 4-6 weeks 2:

• If cough persists beyond 8 weeks total duration, reclassify as chronic cough and pursue comprehensive evaluation including spirometry 1, 2
• For chronic cough, the most common causes are upper airway cough syndrome, asthma, gastroesophageal reflux disease, and nonasthmatic eosinophilic bronchitis, accounting for approximately 90% of cases 5, 4
• Consider chest CT only if chest radiograph is abnormal, empiric treatments fail, or there is clinical suspicion of underlying pulmonary disease 1

Common Pitfalls to Avoid

• Don't use subtherapeutic doses of dextromethorphan (standard OTC doses of 15-30 mg are often inadequate; use 60 mg) 3
• Don't prescribe antibiotics for postinfectious cough unless bacterial infection is confirmed 1, 2
• Don't overlook pertussis in adults with prolonged paroxysmal cough 2
• Don't perform chest CT as initial investigation when chest radiograph is normal and common causes haven't been addressed 1
• Don't forget that multiple causes often coexist requiring additive treatment approaches 1, 6