What is the treatment for hypersensitivity pneumonitis?

Treatment of Hypersensitivity Pneumonitis

The cornerstone of treatment for hypersensitivity pneumonitis (HP) is complete avoidance of the inciting antigen, which should be the first intervention for all patients regardless of disease severity or classification. 1

Disease Classification and Treatment Approach

HP is classified into two main phenotypes that guide treatment:

1. Nonfibrotic HP

• Primary treatment: Complete antigen avoidance
• Clinical response: Often results in significant improvement or complete resolution
• Monitoring: Follow lung function and symptoms after antigen removal

2. Fibrotic HP

• Primary treatment: Complete antigen avoidance
• Additional therapy: Typically requires immunosuppressive treatment
• Prognosis: Less favorable than nonfibrotic HP, may progress despite antigen removal

Treatment Algorithm

1. Identify and eliminate exposure to inciting antigen

   • Conduct thorough environmental and occupational exposure history
   • Consider serum IgG testing against potential antigens 1
   • For occupational exposures, consider consultation with occupational medicine specialist and environmental hygienist 1
   • For home exposures, remediation or relocation may be necessary 2, 3

2. Assess disease severity and fibrotic status

   • Classify as fibrotic or nonfibrotic based on HRCT findings 1
   • Evaluate pulmonary function tests for severity assessment

3. Pharmacological management

   • For severe disease or respiratory failure: Prednisone 1-2 mg/kg/day tapered over 4-8 weeks 1
   • For fibrotic HP: Consider longer-term immunosuppressive therapy
   • For immunocompromised patients or those with persistent disease: Consider antimicrobial drugs with activity against potential microbial antigens (if relevant) 1

Special Considerations

Hot Tub Lung (MAC-related HP)

• Complete avoidance of indoor hot tub exposure is mandatory
• For indoor hot tubs, place outdoors or consider complete removal 1
• For severe disease, add prednisone 1-2 mg/kg/day tapered over 4-8 weeks 1

Metal Worker's HP (M. immunogenum)

• Complete avoidance of metal-working fluid exposure
• Consider corticosteroid administration for clinical improvement 1

Monitoring and Follow-up

• Regular assessment of lung function (FVC, DLCO)
• Follow-up HRCT to evaluate disease progression or improvement
• Continued vigilance for potential re-exposure to antigens

Common Pitfalls and Caveats

1. Failure to identify the antigen: In 30-60% of cases, the inciting antigen cannot be identified 4, but continued efforts to identify it should persist as long as diagnostic uncertainty remains 1

2. Inadequate antigen avoidance: Partial avoidance may result in continued disease progression; complete elimination is necessary 1

3. Misdiagnosis: HP can mimic other interstitial lung diseases, leading to inappropriate treatment 5

4. Delayed treatment: Early detection and prompt removal of the causative agent is critical for favorable outcomes; delayed intervention may lead to irreversible fibrosis 2, 6

5. Overlooking progression despite antigen removal: Some cases of fibrotic HP may continue to progress despite appropriate antigen avoidance, requiring additional immunosuppressive therapy 4

The evidence clearly demonstrates that antigen avoidance is the most critical intervention for HP treatment, with pharmacological therapy serving as an adjunct for more severe or persistent cases. Prognosis is generally favorable with early detection and prompt removal of the causative antigen, but can progress to fatal disease with continued exposure or in cases of fibrotic HP 2.