What is the management of hypersensitivity pneumonitis?

Management of Hypersensitivity Pneumonitis

The cornerstone of hypersensitivity pneumonitis (HP) management is complete antigen avoidance as first-line approach, followed by systemic corticosteroids for patients with physiologic impairment, and consideration of immunosuppressive agents for steroid-sparing effects. 1

Classification and Initial Assessment

HP is classified into two main phenotypes that guide management:

• Non-fibrotic HP: Generally better prognosis
• Fibrotic HP: Associated with worse outcomes and higher mortality

Exposure Identification and Avoidance

1. Thorough exposure history:

   • Use comprehensive environmental and occupational questionnaires tailored to geographic region 2
   • Consider involving occupational medicine specialists and environmental hygienists for complex cases 2
   • Classify patients based on likelihood of occupational or environmental inciting antigen exposure 2

2. Common sources of exposure:

   • Occupational: Farming, bird breeding, wood processing, metal working, swimming facilities
   • Home: Contaminated humidifiers, air conditioners, hot tubs, pet birds, moldy areas
   • Hobbies: Hot tub use, bird keeping, woodworking 1

3. Antigen avoidance strategies:

   • Complete antigen avoidance (CAA) is essential - patients with CAA have no recurrence or development of fibrosis 3
   • When remediation is impossible, remove patient from the suspected environment 1
   • Specific interventions: avoiding indoor hot-tub use for hot-tub lung, avoiding metalworking fluid exposure for metal grinders 1

Treatment Algorithm

1. Non-Fibrotic HP

• First-line: Complete antigen avoidance 1
• Second-line: Short course of corticosteroids for symptomatic relief if needed
• Monitoring: Regular assessment of FVC% and DLCO%, which typically improve after exposure avoidance 1

2. Fibrotic HP

• First-line: Complete antigen avoidance 1

• Second-line: Corticosteroids for patients with physiologic impairment

  • Typical regimen: Prednisone 0.5-1 mg/kg/day with gradual tapering based on clinical response 1
  • For severe disease or respiratory failure: Higher-dose corticosteroids with duration based on clinical response 1

• Third-line: Early transition to steroid-sparing agents

  • Preferred agents: Azathioprine or mycophenolate mofetil 1
  • Consider these agents to reduce treatment-emergent adverse events from long-term steroid use 1

• For progressive disease despite treatment: Consider nintedanib (tyrosine kinase inhibitor) 1, 4

  • FDA-approved for slowing progression of chronic fibrosing ILDs with progressive phenotype, including HP 4

Monitoring and Follow-up

• Regular assessment of:

  • Clinical symptoms
  • Pulmonary function tests (FVC, DLCO)
  • Radiographic changes 1

• Continue long-term corticosteroid therapy only if objective improvement is documented 1

• More vigilant monitoring for patients with risk factors for poor outcomes:

  • Unidentified inciting antigens (HR 1.76-2.08 for shortened survival) 1
  • Presence of fibrosis 1
  • <50% lymphocytes in bronchoalveolar lavage 3
  • Honeycombing on imaging 3
  • Telomere-related gene mutations 1

Supportive Care

• Oxygen therapy for hypoxemic patients
• Pulmonary rehabilitation
• Consider lung transplantation for end-stage disease 1, 4

Common Pitfalls to Avoid

1. Failure to identify and remove the inciting antigen - occurs in 30-60% of cases despite thorough investigation 1
2. Continuing corticosteroids without documented objective improvement
3. Overlooking progression to fibrotic disease requiring adjustment in management approach
4. Delaying transition to steroid-sparing agents in patients requiring long-term immunosuppression
5. Missing the development of a progressive fibrotic phenotype that might benefit from antifibrotic therapy

By following this structured approach to HP management with emphasis on antigen avoidance and appropriate pharmacotherapy based on disease phenotype and progression, clinicians can optimize outcomes for patients with this complex interstitial lung disease.