What is the treatment for hypersensitivity pneumonitis?

Treatment of Hypersensitivity Pneumonitis

The cornerstone of treatment is complete and immediate removal of the inciting antigen, which must be combined with corticosteroids (prednisone 1-2 mg/kg/day tapered over 4-8 weeks) for severe non-fibrotic disease or respiratory failure. 1, 2

Initial Classification: Fibrotic vs Non-Fibrotic Disease

Before initiating treatment, you must classify the patient as having either non-fibrotic or fibrotic HP, as this fundamentally determines prognosis and treatment approach 1, 2:

• Non-fibrotic HP: Purely inflammatory disease without radiographic or histopathologic fibrosis; has significantly better prognosis with potential for complete recovery 2
• Fibrotic HP: Presence of fibrosis on imaging or pathology; carries substantially worse prognosis and often shows limited response to immunosuppression 2

Antigen Identification and Complete Avoidance

Systematic Exposure Evaluation

Conduct a three-component assessment to identify the causative antigen 2:

• Exposure survey: Document all potential organic antigens, inorganic chemicals, and pharmaceutical agents 2
• Occupational history: For work-related exposures, immediately consult an occupational medicine specialist and certified environmental hygienist 2
• Environmental history: Assess home exposures including pet birds (pigeons, parakeets), contaminated humidifiers, indoor molds, and hot tubs 1, 3

Complete Antigen Removal (Not Partial Measures)

Partial avoidance is insufficient and will result in treatment failure 2:

• For hot-tub lung or mycobacterial HP, the indoor hot tub must be moved outdoors or completely removed—not just cleaned 1, 2
• For occupational exposures, worker removal from the exposure site is mandatory if disease recurs despite workplace modifications 2
• Clinical improvement after complete antigen avoidance in fibrotic HP reduces mortality (HR 0.18; 95% CI 0.04-0.77) 1

Pharmacological Management

Non-Fibrotic HP

For severe disease or respiratory failure 1, 2:

• Initiate prednisone 1-2 mg/kg/day, tapered over 4-8 weeks 1, 2
• Corticosteroids hasten recovery and improve gas exchange but must be combined with antigen avoidance 1, 2
• For mycobacterial HP (hot-tub lung), add antimycobacterial therapy for 3-6 months if symptoms persist after complete antigen avoidance 1, 2

Fibrotic HP

For progressive fibrotic disease 1:

• Higher doses of corticosteroids may be needed for longer periods, though response is often limited 4
• Consider immunosuppressive agents (mycophenolate mofetil or azathioprine) as steroid-sparing agents when complete antigen avoidance cannot be achieved or for patients requiring prolonged therapy 1, 4
• Long-term corticosteroid therapy should only be continued if objective improvement in clinical signs, pulmonary function, or radiographic abnormalities is documented 5

Monitoring and Follow-Up Protocol

Establish systematic surveillance with specific timing 1, 2:

• Baseline assessment: Measure FVC%, DLCO%, and gas exchange parameters 2
• Follow-up timing: Reassess at 3-4 months after antigen avoidance in non-fibrotic cases, as improvement in lung function typically occurs within this timeframe 1, 4
• Every visit: Perform continued surveillance for exposure and reinforce patient education on antigen avoidance 1, 2

Critical Pitfalls to Avoid

Do not make these common errors 1, 4:

• Failing to ensure complete cessation of antigen exposure before escalating immunosuppression—this is the most common cause of treatment failure 4
• Assuming lack of improvement rules out HP—failure to improve with antigen avoidance does not exclude HP, especially in fibrotic disease 1
• Relying solely on clinical improvement with medical therapy to confirm or rule out HP diagnosis—this approach is not recommended 1, 4
• Overlooking the need for steroid-sparing agents in patients requiring prolonged therapy 4

Special Populations and Considerations

For patients with unidentified antigens (common in fibrotic HP) 1, 2:

• More aggressive immunosuppression may be necessary 1
• Consider early antifibrotic therapy if progressive phenotype develops, particularly in patients with UIP-like pattern on imaging who have particularly poor prognosis 2

For immunocompromised patients or persistent disease 1, 2:

• Consider antimicrobial therapy if symptoms persist despite antigen avoidance and corticosteroids 1, 2

Smoking cessation 2:

• Address smoking as part of comprehensive management, as it is associated with poor prognosis 2