What are the current treatment guidelines for hypersensitivity pneumonitis?

Current Treatment Guidelines for Hypersensitivity Pneumonitis

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

Classification and Initial Assessment

• HP should be classified into two clinical phenotypes: non-fibrotic and fibrotic HP, as treatment approaches differ based on this classification 1
• A thorough environmental and occupational exposure history is essential to identify potential inciting antigens (IAs) 1
• For occupational exposures, consider involving an occupational medicine specialist and environmental hygienist during the diagnostic workup 1
• Clinical improvement after complete antigen avoidance supports the diagnosis of HP, though lack of improvement does not rule out the disease 1, 2

Treatment Algorithm for Non-Fibrotic HP

• First-line treatment: Complete antigen avoidance 1, 3
• For patients with severe symptoms or respiratory failure:
  • Prednisone 1-2 mg/kg/day tapered over 4-8 weeks 3
  • Corticosteroids may hasten recovery but should always be used in conjunction with antigen avoidance 3, 4
• For mycobacterial HP (e.g., hot-tub lung):
  • Complete removal of antigen source 3
  • Consider antimycobacterial therapy for 3-6 months if symptoms persist despite antigen avoidance 3

Treatment Algorithm for Fibrotic HP

• First-line treatment: Complete antigen avoidance 1, 3
• For progressive disease or when complete antigen avoidance cannot be achieved:
  • Immunosuppressive therapy with corticosteroids 3, 4
  • Clinical improvement after antigen avoidance in fibrotic HP is associated with decreased mortality 3
• For cases with progressive fibrosis despite treatment:
  • Consider antifibrotic therapy, though evidence is limited 4

Monitoring and Follow-up

• Regular assessment of lung function (FVC%, DLCO%) is essential to monitor treatment response 3, 4
• In non-fibrotic HP, improvement in lung function parameters typically occurs within 3-4 months after antigen avoidance 3
• Continued surveillance for exposure and patient education focused on antigen avoidance should be performed at every visit 3, 5

Special Considerations

• In cases where the inciting antigen cannot be identified (up to 60% of patients), more aggressive immunosuppression may be necessary 3, 2
• For patients with fibrotic HP who continue to progress despite antigen avoidance, consider referral to a specialized center 1, 6

Common Pitfalls and Caveats

• Failure to improve with antigen avoidance does not rule out HP, especially in fibrotic disease 1, 7
• Relying solely on clinical improvement with medical therapy to confirm or rule out HP diagnosis is not recommended 1
• Complete antigen avoidance may be difficult to achieve, particularly when the source is unclear or in occupational settings 5, 6
• Some patients with fibrotic HP may evolve to a progressive phenotype despite complete exposure avoidance 4