Treatment of Hypersensitivity Pneumonitis
The primary treatment for hypersensitivity pneumonitis (HP) is complete avoidance of the inciting antigen, which should be implemented immediately upon diagnosis and is essential for improving survival outcomes. 1
Classification and Diagnostic Considerations
- HP should be classified based on the presence or absence of fibrosis, as fibrotic HP has significantly worse prognosis than non-fibrotic HP 1
- Identification of the inciting antigen is crucial for management and has significant implications for survival 2, 1
- A thorough environmental and occupational exposure history is essential to identify potential inciting antigens 2
- Consider consulting an occupational medicine specialist and environmental hygienist during the diagnostic workup of suspected occupational HP cases 2
Treatment Algorithm
Step 1: Antigen Identification and Avoidance
- Complete antigen avoidance is the cornerstone of treatment for all forms of HP 1, 3
- For occupational exposures, workplace modifications or job changes may be necessary 2
- For home exposures (e.g., bird proteins, mold, contaminated humidifiers), remediation or relocation should be considered 1, 4
- For hot-tub lung or mycobacterial-related HP, the source should be removed or relocated outdoors 1
Step 2: Pharmacological Management Based on HP Type
For Non-fibrotic HP:
- For patients with severe symptoms or respiratory failure, initiate prednisone at 1-2 mg/kg/day tapered over 4-8 weeks 1, 3
- Corticosteroids may hasten recovery and improve gas exchange but should always be used in conjunction with antigen avoidance 1, 4
- In cases of mycobacterial HP (hot-tub lung), consider antimycobacterial therapy for 3-6 months if symptoms persist despite antigen avoidance 1
For Fibrotic HP:
- Immunosuppressive therapy is indicated when complete antigen avoidance cannot be achieved or when disease progresses despite antigen avoidance 1, 3
- Clinical improvement after antigen avoidance in fibrotic HP is associated with decreased mortality (HR, 0.18; 95% CI, 0.04-0.77) 1
- For progressive fibrotic HP, antifibrotic therapy may be considered to slow disease progression 3, 4
Monitoring and Follow-up
- Regular assessment of lung function (FVC%, DLCO%) is essential to monitor treatment response 1, 3
- In non-fibrotic HP, improvement in lung function parameters typically occurs within 3-4 months after antigen avoidance 1
- Continued surveillance for exposure and patient education focused on antigen avoidance should be performed at every visit 1, 3
Common Pitfalls and Caveats
- Failure to identify the inciting antigen significantly worsens prognosis 1, 5
- Failure to improve with antigen avoidance does not rule out HP, especially in fibrotic disease 1, 5
- Relying solely on clinical improvement with medical therapy to confirm or rule out HP diagnosis is not recommended 1
- Immunosuppressive agents have not been shown to slow the worsening of fibrotic disease in controlled trials 3
- Some patients with fibrotic HP may evolve to a progressive phenotype even with complete exposure avoidance 4
Special Considerations
- For patients with unidentified inciting antigens (common in fibrotic HP), more aggressive immunosuppression may be necessary 1, 3
- For immunocompromised patients or those with persistent disease despite antigen avoidance and corticosteroids, consider antimicrobial therapy 1
- Non-pharmacological interventions such as oxygen therapy, pulmonary rehabilitation, and supportive care are important components of overall care for patients with progressive HP 3