What is the recommended management for Farmer's lung (hypersensitivity pneumonitis)?

Management of Farmer's Lung (Hypersensitivity Pneumonitis)

Complete and immediate removal from moldy hay exposure is the single most critical intervention and the only treatment that can achieve complete disease resolution in Farmer's lung. 1, 2

Initial Classification

Classify the patient as either non-fibrotic or fibrotic HP, as this determines prognosis and treatment intensity 1, 3:

• Non-fibrotic HP: Purely inflammatory disease without radiographic or histopathologic fibrosis 3
• Fibrotic HP: Presence of fibrosis on imaging or pathology, which carries significantly worse prognosis and mortality 1, 3

Antigen Identification and Complete Avoidance

This is the cornerstone of treatment and supersedes all pharmacologic interventions 2:

• Conduct a systematic three-component exposure evaluation: exposure survey, occupational history targeting thermophilic actinomycetes and fungi from moldy hay, straw, or grain 2, 4, 5
• The most common causative organisms in Farmer's lung are thermophilic actinomycetes (especially Micropolyspora faeni), Absidia corymbifera, Eurotium species, and various fungi 6, 4, 5
• Partial antigen reduction is insufficient—complete removal from the farm environment is mandatory 2
• If the hay storage area cannot be completely remediated, remove the patient from the farm environment within days 2
• High-risk conditions include: bad climatic harvest conditions, high-density hay-packing (especially round bales), and high altitude storage 4

Expected Response Timeline

• Clinical improvement typically occurs within 2 weeks to 3.4 months after complete antigen cessation 2
• Lung function improvement averages 3.4 ± 2.4 months after antigen avoidance 2
• Monitor FVC% and DLCO% at 3-4 months to assess response 1, 3

Pharmacologic Management

Non-Fibrotic Farmer's Lung

Corticosteroids are reserved ONLY for severe disease or respiratory failure, not for routine cases 2:

• For severe disease or respiratory failure: Prednisone 1-2 mg/kg/day tapered over 4-8 weeks 7, 1, 3, 2
• Corticosteroids hasten recovery and improve gas exchange but must always be combined with complete antigen avoidance 7, 1, 2
• Corticosteroids accelerate resolution of acute symptoms but do not prevent long-term progression or reduce mortality 5

Fibrotic Farmer's Lung

• Clinical improvement after antigen avoidance reduces mortality (HR 0.18; 95% CI 0.04-0.77) 1
• When complete antigen avoidance cannot be achieved, immunosuppressive therapy may be needed for progressive disease 1
• More aggressive immunosuppression may be necessary when the inciting antigen cannot be completely eliminated 1

Diagnostic Workup to Support Management

While managing the patient, confirm diagnosis through 7:

• HRCT findings: Profuse centrilobular ground-glass nodules, inspiratory mosaic attenuation, air-trapping, three-density sign 7
• Serum IgG testing: Against thermophilic actinomycetes and fungal antigens (sensitivity 83%, specificity 68% for distinguishing HP from other ILDs) 7
• BAL fluid analysis: Lymphocytosis (mean difference 30% higher than IPF) supports diagnosis but is not required if exposure history and HRCT are typical 7
• Lung biopsy: Consider only when clinical, laboratory, radiologic, and bronchoscopic findings don't yield confident diagnosis 7

Monitoring and Follow-Up

• Establish baseline FVC%, DLCO%, and gas exchange parameters 3
• Reassess at 3-4 months after antigen avoidance in non-fibrotic cases 1, 3
• Continue surveillance for re-exposure at every visit with reinforcement of antigen avoidance education 1, 3, 2

Critical Pitfalls to Avoid

• Never escalate immunosuppression without ensuring complete antigen avoidance first—this is the most common management error 2
• Do not rely solely on clinical improvement with medical therapy to confirm diagnosis 1
• Failure to improve with antigen avoidance does not rule out HP, especially in fibrotic disease 1
• Partial measures (e.g., wearing masks while handling hay) are insufficient—complete removal from exposure is required 2

Prevention Strategies

• Educate patients on proper hay storage to prevent mold growth: avoid high-density packing, ensure adequate drying before storage, and avoid harvesting in poor weather conditions 4, 5
• For patients with documented Farmer's lung, complete avoidance of moldy hay exposure is paramount to prevent recurrence 2