What is the treatment for hypersensitivity pneumonitis?

Treatment of Hypersensitivity Pneumonitis

The cornerstone of hypersensitivity pneumonitis treatment is complete and immediate removal of the inciting antigen, combined with systemic corticosteroids in patients with physiologic impairment, with treatment strategy fundamentally determined by whether fibrosis is present or absent. 1, 2, 3

Initial Classification: Fibrotic vs. Non-Fibrotic Disease

The first critical step is determining whether the patient has fibrotic or non-fibrotic HP, as this distinction fundamentally alters prognosis and treatment approach. 2, 3

• Non-fibrotic HP shows purely inflammatory disease without radiographic or histopathologic fibrosis and has significantly better prognosis with potential for complete recovery 3
• Fibrotic HP demonstrates fibrosis on imaging or pathology, carries substantially worse prognosis, and often shows limited response to immunosuppression even with treatment 3, 4

Antigen Identification and Complete Avoidance

Exposure Assessment Strategy

Conduct a systematic three-component evaluation including exposure survey, occupational history, and environmental history to identify organic antigens, inorganic chemicals, and pharmaceutical agents. 3

• For occupational exposures, immediately consult an occupational medicine specialist and certified environmental hygienist during diagnostic workup 3
• Obtain detailed history about birds, hot tubs, humidifiers, mold exposure, workplace chemicals, and hobbies 1

Complete Antigen Removal (Not Partial Measures)

Partial avoidance measures are insufficient and will result in treatment failure. 3

• For hot-tub lung or mycobacterial HP, the indoor hot tub must be moved outdoors or completely removed—cleaning or reducing use is inadequate 2, 3
• For occupational HP, worker removal from the exposure site is mandatory if disease recurs despite workplace modifications 3
• Clinical improvement after complete antigen avoidance in fibrotic HP reduces mortality (HR 0.18; 95% CI 0.04-0.77) 2

Pharmacological Management

Non-Fibrotic HP

For severe disease or respiratory failure:

• Initiate prednisone 1-2 mg/kg/day, tapered over 4-8 weeks 1, 2, 3
• Corticosteroids hasten recovery and improve gas exchange but must be combined with antigen avoidance 2, 3
• Over 80% of symptomatic patients show clinical improvement with corticosteroid therapy 1

For mycobacterial HP (hot-tub lung):

• Add antimycobacterial therapy for 3-6 months if symptoms persist after complete antigen avoidance 2, 3

Fibrotic HP

Treatment approach for fibrotic disease:

• Immunosuppressive therapy may be needed when complete antigen avoidance cannot be achieved 2
• However, recent evidence shows patients with fibrotic HP demonstrate decline in FVC% and DLCO% over one year, and immunosuppression does not modify this risk 4
• Consider antifibrotic therapy as initial choice in fibrotic HP, as decline occurs with or without immunosuppression 4, 5
• For steroid-refractory disease (no improvement after >48 hours), options include infliximab, mycophenolate mofetil, IVIG, or cyclophosphamide 1

Patients with UIP-like pattern on imaging:

• Have particularly poor prognosis and reduced survival 3
• Early consideration of antifibrotic therapy is warranted if progressive phenotype develops 3

Monitoring and Follow-Up Protocol

Baseline Assessment

• Establish baseline FVC%, DLCO%, and gas exchange parameters 2, 3

Follow-Up Timing

• Reassess at 3-4 months after antigen avoidance in non-fibrotic cases 2, 3
• Improvement in lung function parameters typically occurs within this timeframe in non-fibrotic HP 2, 6

Ongoing Surveillance

• Perform continued surveillance for exposure at every visit 2, 3
• Reinforce patient education on antigen avoidance at each encounter 3

Critical Pitfalls to Avoid

Common errors that lead to treatment failure:

1. Accepting partial antigen avoidance rather than insisting on complete removal—this is the most common cause of treatment failure 3, 6

2. Failing to recognize that lack of improvement with antigen avoidance does not rule out HP, especially in fibrotic disease where irreversible damage may have occurred 2, 6

3. Escalating immunosuppression before ensuring complete cessation of antigen exposure—always verify complete avoidance first 6

4. Relying solely on clinical improvement with medical therapy to confirm or rule out HP diagnosis—this approach is not recommended 2, 6

5. Missing the diagnosis entirely because clinical presentation is extremely variable and the causative antigen may not be immediately apparent 1, 7

6. Using corticosteroids alone in fibrotic HP without considering antifibrotic therapy, as immunosuppression may not prevent decline in this population 4, 5

Special Populations

Immunocompromised patients or persistent disease:

• Consider antimicrobial therapy if symptoms persist despite antigen avoidance and corticosteroids 2, 3

Patients with familial interstitial lung disease:

• Demonstrate decline in FVC% and DLCO% over one year, and immunosuppression does not modify this risk 4

Smokers:

• Smoking is associated with poor prognosis and must be addressed as part of comprehensive management 3