What is the next step in managing a patient with a persistent cough for 2 months despite consultations with an allergist and a primary care physician (PCP)?

Next Steps for Persistent Cough After Initial Consultations

The patient requires a systematic diagnostic workup starting with chest radiograph and spirometry, followed by sequential empiric treatment trials targeting the three most common causes: upper airway cough syndrome (UACS), asthma, and gastroesophageal reflux disease (GERD), which together account for approximately 90% of chronic cough cases. 1

Immediate Baseline Investigations

Essential First-Line Testing

• Obtain a chest radiograph immediately if not already done, as this is mandatory for all patients with chronic cough (>8 weeks) and can identify abnormalities in 31% of cases 2
• Perform spirometry with bronchodilator response to identify airflow obstruction and assess for asthma, as this should be done in all patients with chronic cough 2
• Note that normal spirometry does not exclude asthma as a cause, since many patients with cough-variant asthma lack spirometric reversibility 2

Sequential Empiric Treatment Approach

Given that the patient has already seen an allergist and PCP without resolution, you should now implement a structured algorithmic approach:

First: Treat Upper Airway Cough Syndrome (UACS)

• Initiate a first-generation antihistamine-decongestant combination as the initial empiric therapy 1
• Look for clinical clues: nasal discharge, throat clearing, postnasal drip sensation 1
• UACS (previously called postnasal drip syndrome) is one of the most common causes in specialist cough clinics 2

Second: Treat Asthma (if UACS treatment fails)

• Start empiric trial of inhaled bronchodilators and/or inhaled corticosteroids 1
• If spirometry is normal but asthma is still suspected, consider bronchoprovocation challenge testing 1
• For patients with normal spirometry in whom cough-predominant asthma or eosinophilic bronchitis is suspected, offer a therapeutic trial of oral prednisolone 2
• Look for triggers: cold air, exercise, nighttime worsening 1

Third: Treat GERD (if above treatments fail)

• Initiate high-dose proton pump inhibitor (PPI) therapy along with dietary modifications and lifestyle changes 1
• This is recommended for patients with the following profile: cough >2 months, normal chest radiograph, nonsmoker, not on ACE inhibitors, failed treatment for UACS and asthma 2
• Look for heartburn, regurgitation, or sour taste, though GERD can cause cough without typical GI symptoms 2
• Response time is variable—some patients respond within 2 weeks, others may take several months 2

Advanced Diagnostic Testing (If Empiric Trials Fail)

When to Pursue Further Workup

If the patient has undergone adequate therapeutic trials of the above three conditions without improvement, consider:

• High-resolution CT (HRCT) scan of chest to evaluate for bronchiectasis, interstitial lung disease, or occult masses 1
• 24-hour esophageal pH monitoring if GERD is suspected but empiric PPI therapy failed, though interpretation can be problematic 2, 1
• Bronchoscopy to evaluate for endobronchial lesions, sarcoidosis, eosinophilic bronchitis, or occult infection 1
• Consider pertussis testing (nasal swab for Bordetella), as 10% of chronic cough cases in one series were positive 2

Treatment of Unexplained Chronic Cough

If systematic evaluation and adequate therapeutic trials have been completed without identifying a cause:

• Consider a trial of gabapentin starting at 300 mg once daily, escalating as tolerated to maximum 1,800 mg daily in divided doses 2, 1
• Discuss potential side effects and reassess risk-benefit at 6 months before continuing 2, 1
• Multimodality speech pathology therapy is a reasonable alternative approach 2, 1
• Do NOT prescribe inhaled corticosteroids if bronchial hyperresponsiveness and eosinophilia testing are negative 2, 1
• Do NOT continue PPI therapy if objective testing for acid reflux is negative 2, 1

Critical Pitfalls to Avoid

• Inadequate treatment duration: Each therapeutic trial must be given sufficient time before declaring failure—stopping therapy prematurely is a common error 1
• Failing to recognize multiple simultaneous causes: Some patients require combined therapy for more than one condition 1
• Diagnosing "unexplained cough" prematurely: This diagnosis should only be made after completing systematic evaluation with objective testing and adequate therapeutic trials according to published guidelines 2, 1
• Assuming the allergist and PCP have completed the full workup: Verify that chest radiograph, spirometry, and sequential empiric trials were actually performed with adequate duration and dosing 2