What is the best course of treatment for a patient with a chronic cough, decreased diffusing capacity of the lungs for carbon monoxide (DLCO) at 79%, normal 6-minute walk (6MW) test, and positive lab tests for mold exposure, with a background of suspected interstitial lung disease (ILD) and possible underlying conditions such as asthma or chronic obstructive pulmonary disease (COPD)?

Management of Chronic Cough in a Patient with Suspected Hypersensitivity Pneumonitis from Mold Exposure

The most critical first step is immediate and complete removal of the mold exposure, combined with systemic corticosteroid therapy given the evidence of physiologic impairment (decreased DLCO), as this represents hypersensitivity pneumonitis (HP) until proven otherwise. 1, 2

Immediate Priority: Identify and Remove Mold Exposure

• Environmental remediation is the cornerstone of treatment - the patient must immediately cease all exposure to the mold source and arrange for professional remediation of the contaminated environment 1, 2
• Home mold exposure from chronic water intrusion (bathrooms, bedrooms, air conditioning units) is a commonly overlooked cause of HP and requires thorough environmental assessment 3
• The positive lab test for mold exposure combined with hyperinflation, decreased DLCO (79%), and chronic cough strongly suggests HP as the primary diagnosis 4, 3

Rule Out Alternative Causes Before Attributing Cough to ILD

Before confirming HP as the sole cause of cough, you must systematically exclude common alternative etiologies, as these may coexist and require specific treatment 1, 2:

• Gastroesophageal reflux disease (GERD) - particularly important as GERD commonly coexists with ILD and can independently cause chronic cough 1, 2
• Upper airway cough syndrome (previously postnasal drip syndrome) - must be evaluated and treated if present 1, 2
• Asthma or nonasthmatic eosinophilic bronchitis - the hyperinflation on PFTs raises concern for concurrent airway disease that requires specific therapy 1, 2
• Medication side effects - review all current medications for potential cough-inducing agents 2

Corticosteroid Therapy for Hypersensitivity Pneumonitis

Systemic corticosteroids are indicated for HP with evidence of physiologic impairment (your patient has decreased DLCO at 79%) 1, 4:

• Initiate oral corticosteroids after confirming exposure removal and ruling out pulmonary infection 1, 4
• The decreased DLCO indicates gas exchange impairment that warrants immunosuppressive therapy 4
• Early diagnosis and treatment are critical to prevent progression to fibrotic disease 4

Important Diagnostic Considerations

Confirm the HP diagnosis with the following approach 2, 4, 5:

• High-resolution CT (HRCT) chest to look for ground-glass opacities, poorly defined nodules, and patchy air trapping characteristic of subacute HP 4
• Consider bronchoscopy with bronchoalveolar lavage if diagnosis remains uncertain - expect lymphocytosis in BALF 4, 6
• Serum precipitins to mold antigens may support the diagnosis but are not required 5
• The diagnosis requires: (1) exposure to known antigen (mold), (2) compatible clinical presentation (cough, decreased DLCO), (3) temporal relationship, and (4) improvement with exposure removal 4, 5

Management of Refractory Cough

If cough persists despite treating HP and excluding alternative causes, proceed with therapies for refractory ILD-associated cough 1, 2:

• Gabapentin as first-line therapy for refractory cough, using dosing protocols for unexplained chronic cough (typically starting 300mg daily, titrating to effect) 1, 2
• Multimodality speech pathology therapy with cough suppression techniques and breathing exercises as first-line option 1, 2
• Low-dose controlled-release morphine as second-line therapy if gabapentin and speech therapy fail 1, 2

Critical Pitfalls to Avoid

• Do NOT use inhaled corticosteroids for chronic cough in ILD - three trials showed no benefit in sarcoidosis, and they are not recommended for HP-associated cough 1, 2
• Do NOT prescribe proton pump inhibitors empirically without documented GERD, as they are not recommended for ILD patients with negative reflux workup 1, 2
• Do NOT delay environmental assessment - personally inspect the patient's home environment if necessary, as domestic mold exposures are often difficult to identify 5
• Do NOT assume the normal 6-minute walk test excludes significant disease - DLCO impairment can exist with preserved exercise capacity, and cough itself has prognostic significance in ILD 1

Monitoring and Follow-up

• Reassess symptoms, pulmonary function tests (especially DLCO), and chest imaging 4-6 weeks after exposure removal and corticosteroid initiation 4
• Improvement in FVC >10% occurs in only 12% of patients who remove exposure, so lack of improvement doesn't indicate treatment failure 3
• If fibrotic changes develop on HRCT, the prognosis worsens significantly and may require consideration for antifibrotic therapy or lung transplantation in advanced cases 4