Management of Hypersensitivity Pneumonitis
The cornerstone of hypersensitivity pneumonitis management is complete and permanent antigen avoidance, which must be prioritized before any pharmacologic intervention, as this represents the only truly effective treatment and carries the best medical prognosis. 1, 2, 3
Initial Classification and Risk Stratification
Immediately classify the patient based on the presence or absence of fibrosis, as this fundamentally determines treatment approach and prognosis 1, 2:
- Non-fibrotic HP: Better prognosis with potential for complete recovery; responds well to antigen avoidance alone 2, 4
- Fibrotic HP: Significantly worse prognosis with limited response to immunosuppression; may require antifibrotic therapy 1, 5, 6
Antigen Identification and Avoidance Strategy
Exposure Assessment
Obtain a detailed environmental and occupational exposure history focusing on the type, extent, and temporal relationship between exposures and symptoms 1, 7. Common sources include 7:
- Avian antigens (birds, feather bedding)
- Indoor molds and contaminated humidifiers
- Hot tubs (mycobacterial exposure)
- Occupational exposures (metalworking fluids, isocyanates)
For occupational exposures, involve an occupational medicine specialist and environmental hygienist during workup, especially when the source is unclear 1, 7.
Antigen Remediation
Complete and definitive antigen avoidance is mandatory 1, 2:
- For hot tub-related HP: Remove indoor hot tubs completely or move outdoors 2, 7
- For occupational exposures: Complete workplace avoidance may be necessary 7
- For avian exposure: Remove all birds and feather-containing materials from the home 7
Critical pitfall: Partial avoidance is insufficient—continued low-level exposure can perpetuate disease progression despite treatment 1, 2.
Pharmacologic Management
Non-Fibrotic HP
For severe disease or respiratory failure, initiate prednisone 1-2 mg/kg/day tapered over 4-8 weeks 2, 7. Corticosteroids may hasten recovery and improve gas exchange but must be combined with antigen avoidance 2.
For mycobacterial HP (hot tub lung), consider antimycobacterial therapy for 3-6 months if symptoms persist after antigen avoidance 2.
Fibrotic HP
The treatment algorithm differs substantially 1, 5:
First-line: Antigen avoidance remains paramount, as clinical improvement after avoidance is associated with decreased mortality (HR 0.18; 95% CI 0.04-0.77) 2
Second-line immunosuppression: When complete antigen avoidance cannot be achieved or disease progresses despite avoidance, consider immunosuppressive therapy 2, 6:
Third-line antifibrotic therapy: Consider only in progressive fibrotic disease despite immunosuppression 1, 5, 6
Critical distinction from IPF: Unlike idiopathic pulmonary fibrosis where antifibrotics are first-line, in fibrotic HP they are considered secondarily only after antigen avoidance and immunosuppression have been attempted 1, 5.
Monitoring and Follow-Up
Assess lung function (FVC%, DLCO%) regularly to monitor treatment response 1, 2:
- In non-fibrotic HP, improvement typically occurs within 3-4 months after antigen avoidance 1, 2
- Continued surveillance for exposure and patient education should occur at every visit 2, 7
Prognostic Factors
Patients with unidentified inciting antigens have significantly worse survival (HR 2.08; 95% CI 1.02-4.24) compared to those with identified antigens 7. This underscores the critical importance of thorough exposure assessment.
Key Pitfalls to Avoid
Failure to improve with antigen avoidance does not rule out HP, especially in fibrotic disease where measurable clinical improvement may not occur if 1, 2:
- The remediated antigen is not causative
- Multiple exposures are causing disease
- Complete avoidance cannot be achieved
- Severe or progressive pulmonary fibrosis is present
Do not rely solely on clinical improvement with medical therapy to confirm or rule out HP diagnosis 2, 7.
Avoid immunosuppression in IPF: This therapy is harmful in IPF but beneficial in HP, making accurate distinction between these entities critical before initiating treatment 1, 5.