What is the treatment for chronic hypersensitivity pneumonitis?

Treatment of Chronic Hypersensitivity Pneumonitis

The treatment of chronic hypersensitivity pneumonitis (HP) should include complete antigen avoidance as the first-line approach, followed by systemic corticosteroids for patients with physiologic impairment, and consideration of immunosuppressive agents like mycophenolate mofetil or azathioprine to reduce treatment-emergent adverse events. 1, 2

Identification and Avoidance of Inciting Antigen

• Identification and complete removal of the inciting antigen is the cornerstone of HP management and the most crucial therapeutic step 1

• Common sources of antigens include:

  • Microorganisms (fungi, bacteria, mycobacteria)
  • Animal proteins (avian proteins, mammalian proteins)
  • Plant materials (wood dust, vegetable dust)
  • Low-molecular-weight chemicals (isocyanates, metals)
  • Contaminated humidifiers, air conditioning systems, hot tubs 1

• When remediation is not possible, removal of the patient from the suspected environment is necessary 1

• Failure to identify and remove the inciting antigen is a key pitfall in management 1

Pharmacological Management

Corticosteroids

• Systemic corticosteroid therapy is recommended for patients with evidence of physiologic impairment 2
• Typical regimen: Prednisone starting at higher doses (e.g., 0.5-1 mg/kg/day) with gradual tapering based on clinical response 1
• Long-term corticosteroid therapy should only be continued if objective improvement is documented 1
• Corticosteroids may lead to symptomatic improvement but have not been proven to have long-term efficacy in prospective clinical trials 2

Immunosuppressive Agents

• For patients requiring immunosuppression, consider:
  • Azathioprine: Associated with 54% fewer treatment-emergent adverse events compared to prednisone alone 3
  • Mycophenolate mofetil: Associated with 66% fewer treatment-emergent adverse events compared to prednisone alone 3
• Early transition to these agents may be appropriate to reduce corticosteroid-related side effects 3

Antifibrotic Therapy

• Nintedanib (tyrosine kinase inhibitor) may be used for fibrotic progressive HP 1, 4
• Particularly beneficial in patients with progressive fibrotic disease despite antigen avoidance and immunosuppressive therapy 4

Management Algorithm Based on Disease Presentation

1. Non-fibrotic HP:

   • Complete antigen avoidance
   • Short course of corticosteroids for symptomatic relief if needed
   • Monitor FVC% and DLCO% (can improve after exposure avoidance) 2

2. Fibrotic HP:

   • Complete antigen avoidance
   • Corticosteroids for physiologic impairment
   • Consider early transition to steroid-sparing agents (azathioprine or mycophenolate mofetil) 3
   • For progressive disease despite treatment: consider nintedanib 1, 4

3. Severe disease or respiratory failure:

   • Immediate high-dose corticosteroids
   • Oxygen therapy for hypoxemic patients 1
   • Consider lung transplantation for end-stage disease 1

Monitoring and Follow-up

• Regular assessment of:
  • Clinical symptoms
  • Pulmonary function tests (FVC, DLCO)
  • Radiographic changes 1
• Pulmonary rehabilitation for appropriate patients 1, 4
• Oxygen therapy for hypoxemic patients 1

Prognostic Considerations

• Patients requiring immunosuppressive therapy generally have worse baseline lung function and increased mortality 1
• Presence of fibrosis significantly impacts prognosis 1, 5
• In many cases (30-60%), an exposure is not identified despite thorough investigation, which is associated with poorer outcomes 2, 1
• Patients with unidentified inciting antigens have shortened survival compared to those with identifiable antigens (HR 1.76-2.08) 2

Treatment Pitfalls to Avoid

• Continuing exposure to the inciting antigen while on immunosuppressive therapy
• Prolonged corticosteroid use without documented objective improvement
• Failure to transition to steroid-sparing agents when long-term therapy is needed
• Overlooking the need for antifibrotic therapy in progressive fibrotic disease
• Delaying referral for lung transplantation evaluation in end-stage disease

Remember that early diagnosis, complete antigen avoidance, and appropriate pharmacological intervention are essential for improving morbidity, mortality, and quality of life in patients with chronic hypersensitivity pneumonitis.