What is the treatment for hypersensitivity pneumonitis?

Treatment of Hypersensitivity Pneumonitis

Complete and immediate avoidance of the inciting antigen is the single most critical intervention for hypersensitivity pneumonitis and must be prioritized above all other treatments, as it is the only intervention proven to reduce mortality in fibrotic disease. 1

Initial Classification and Risk Stratification

Before initiating treatment, you must classify the patient into one of two categories, as this fundamentally determines your therapeutic approach:

• Non-fibrotic HP: Purely inflammatory disease without radiographic or histopathologic evidence of fibrosis 2
• Fibrotic HP: Presence of fibrosis on imaging or pathology, which carries significantly worse prognosis and requires different management 2, 1

The presence of fibrosis is the primary determinant of prognosis and survival, making this distinction clinically essential rather than academic. 2

Antigen Identification and Avoidance Strategy

Exposure Assessment

Conduct a systematic three-component exposure evaluation:

• Exposure survey: Document all potential organic antigens (bird proteins, fungi, bacteria), inorganic chemicals (isocyanates, metals), and pharmaceutical agents 2
• Occupational history: Request material safety data sheets from workplace, list all chemicals/materials handled, and document temporal relationship between work and symptoms 2
• Environmental history: Assess home for water damage, mold, contaminated HVAC systems, humidifiers, hot tubs, and bird exposure 2

When to Involve Specialists

For occupational exposures, immediately consult an occupational medicine specialist and certified environmental hygienist during the diagnostic workup. 2 These specialists can determine exposure likelihood, facilitate worker removal from the antigen source, suggest workplace modifications, and assist with workers' compensation claims. 2

For residential exposures where the antigen source is unclear, consider consultation with a certified indoor environmental quality consultant for visual inspection of the home environment, focusing on: exterior damage (roof, walls, foundation), HVAC systems and humidifiers, and indoor water damage or condensation. 2

Complete Antigen Removal

• Hot-tub lung or mycobacterial HP: The indoor hot tub must be moved outdoors or completely removed—partial measures are insufficient 1
• Bird-related HP: Complete removal of birds from the home and avoidance of environments with bird exposure 3
• Occupational HP: Worker removal from the exposure site is mandatory if disease recurs despite workplace modifications 2

Critical caveat: An inciting antigen cannot be identified in 30-50% of cases evaluated at ILD referral centers, which necessitates more aggressive immunosuppression. 2, 1

Pharmacological Management

Non-Fibrotic HP

For severe disease or respiratory failure:

• Initiate prednisone at 1-2 mg/kg/day (typically 60-80 mg daily for average adult) 1, 4
• Taper over 4-8 weeks 1, 4
• Corticosteroids hasten recovery and improve gas exchange but must be combined with antigen avoidance 1

For mycobacterial HP (hot-tub lung):

• If symptoms persist after complete antigen avoidance, add antimycobacterial therapy for 3-6 months 1

Important limitation: Corticosteroids may provide symptomatic benefit but do not alter long-term outcomes if antigen exposure continues. 5, 6

Fibrotic HP

The treatment approach for fibrotic disease is fundamentally different:

When complete antigen avoidance is achievable:

• Clinical improvement after antigen avoidance reduces mortality (HR 0.18; 95% CI 0.04-0.77) 1
• Monitor closely for 3-4 months for improvement in FVC% and DLCO% 1, 4

When complete antigen avoidance cannot be achieved or disease progresses:

• Immunosuppressive therapy is indicated, though response is often limited 1, 7
• Consider steroid-sparing agents (mycophenolate mofetil or azathioprine) for patients requiring prolonged therapy 4
• For progressive fibrotic HP: Nintedanib (antifibrotic tyrosine kinase inhibitor) is FDA-approved for slowing progression of chronic fibrosing ILDs with progressive phenotype 7

Critical distinction: Unlike non-fibrotic HP, immunosuppression in fibrotic HP has not been shown to slow disease progression, and antifibrotic therapy becomes the priority for progressive disease. 7

Monitoring and Follow-Up

Establish a systematic surveillance protocol:

• Baseline assessment: FVC%, DLCO%, and gas exchange at rest and with exercise 1, 6
• Follow-up timing: Reassess lung function at 3-4 months after antigen avoidance in non-fibrotic cases 1, 4
• Every visit: Perform continued surveillance for exposure and reinforce patient education on antigen avoidance 1

Expected outcomes in non-fibrotic HP: Improvement in lung function parameters typically occurs within 3-4 months after successful antigen avoidance. 1, 4

Expected outcomes in fibrotic HP: Many patients show limited or no improvement despite treatment, and some develop progressive phenotype even with complete exposure avoidance. 4, 3

Critical Pitfalls to Avoid

• Do not rely on clinical improvement with medical therapy alone to confirm or rule out HP diagnosis—this approach is unreliable 1, 4
• Do not escalate immunosuppression before ensuring complete cessation of antigen exposure 4
• Do not assume treatment failure if the patient doesn't improve with antigen avoidance—this is common in fibrotic disease and doesn't rule out HP 1
• Do not use corticosteroids in IPF: The distinction between fibrotic HP and IPF is critical because immunosuppression is harmful in IPF 2
• Do not overlook the need for steroid-sparing agents in patients requiring prolonged corticosteroid therapy 4

Special Populations

Immunocompromised patients or persistent disease:

• Consider antimicrobial therapy if symptoms persist despite antigen avoidance and corticosteroids 1

Patients with UIP-like pattern on imaging:

• These patients have particularly poor prognosis and reduced survival 2
• Early consideration of antifibrotic therapy is warranted if progressive phenotype develops 7

Cigarette smokers:

• Smoking is associated with poor prognosis and should be addressed as part of comprehensive management 2