What is the treatment and management of hypersensitivity pneumonitis?

Treatment and Management of Hypersensitivity Pneumonitis

The cornerstone of hypersensitivity pneumonitis management is complete and immediate removal of the inciting antigen combined with classification into fibrotic versus non-fibrotic disease, as antigen avoidance alone can halt progression and improve survival, while corticosteroids are reserved for severe non-fibrotic cases or respiratory failure. 1

Initial Disease Classification

Classify all patients as either non-fibrotic HP or fibrotic HP based on high-resolution CT chest imaging, as this distinction is the primary determinant of prognosis and survival. 2, 1

• Non-fibrotic HP: Purely inflammatory disease without radiographic evidence of reticular abnormality, traction bronchiectasis, or honeycombing on HRCT 2
• Fibrotic HP: Presence of fibrosis on imaging (reticular abnormality, traction bronchiectasis, honeycombing) or pathology, which carries significantly worse prognosis with median survival of 4.88-8.75 years depending on antigen identification 2, 1

Antigen Identification and Complete Avoidance

Conduct a systematic three-component exposure evaluation including exposure survey, detailed occupational history, and comprehensive environmental history to identify organic antigens, inorganic chemicals, or pharmaceutical agents. 2, 1

Exposure Assessment Protocol

• Complete a comprehensive environmental and occupational questionnaire tailored to your geographic region, focusing on temporal relationship between exposure and symptoms 2
• Specifically inquire about: bird exposure (pigeons, parakeets), contaminated humidifiers, indoor molds, hot tubs, water-based coolants, agricultural dusts, and occupational exposures 3, 4
• For occupational exposures, immediately consult an occupational medicine specialist and certified environmental hygienist during diagnostic workup 2, 1

Antigen Removal Strategy

Complete removal of the inciting antigen is mandatory—partial measures are insufficient and will not prevent disease progression. 1

• For hot-tub lung or mycobacterial HP, the indoor hot tub must be moved outdoors or completely removed, not just cleaned 1
• For occupational exposures, worker removal from the exposure site is mandatory if disease recurs despite workplace modifications 1
• Continue surveillance for exposure and reinforce patient education on antigen avoidance at every visit, as this is the highest priority intervention 2, 1

Common pitfall: An unrevealing exposure history does not exclude HP—continue the exposure investigation process until diagnosis is more certain, as unidentified antigens lead to ongoing exposure with worse survival (median 4.88 years vs 8.75 years for identified antigens in fibrotic HP) 2

Pharmacological Management

Non-Fibrotic HP

For severe non-fibrotic HP or respiratory failure, initiate prednisone at 1-2 mg/kg/day and taper over 4-8 weeks, as corticosteroids hasten recovery and improve gas exchange but must be combined with antigen avoidance. 1, 5

• Corticosteroids are indicated only for severe acute and subacute HP, not for mild cases where antigen avoidance alone suffices 5
• Long-term corticosteroid therapy should be considered only if objective improvement in clinical signs, pulmonary function, or radiographic abnormalities is documented 5

Fibrotic HP

Monitor patients with fibrotic HP for 3-4 months after antigen avoidance for improvement in FVC% and DLCO% before initiating pharmacotherapy, as clinical improvement after antigen avoidance reduces mortality. 1, 2

• Patients with UIP-like pattern on imaging have particularly poor prognosis and reduced survival—consider early antifibrotic therapy if progressive phenotype develops 1
• Corticosteroids for chronic HP should only be used if disease is severe or progressive, with documented objective improvement 5

Special Situations

For mycobacterial HP (hot tub lung), administer antimycobacterial therapy for 3-6 months if symptoms persist after complete antigen avoidance. 1

• In immunocompromised patients or those with persistent disease despite antigen avoidance and corticosteroids, consider antimicrobial therapy 1

Monitoring and Surveillance Protocol

Establish baseline assessment of FVC%, DLCO%, and gas exchange, with follow-up timing of 3-4 months after antigen avoidance in non-fibrotic cases. 1

• For non-fibrotic HP: Monitor for resolution of symptoms and normalization of pulmonary function tests after antigen avoidance 4
• For fibrotic HP: Serial monitoring is essential as disease may progress despite apparent remediation of suspected exposures, suggesting other factors or unidentified exposures 2
• Repeat pulmonary function testing to document objective improvement before continuing long-term therapy 5

Critical warning: Even with appropriate diagnosis and management including antigen avoidance and corticosteroids, the disease course can be progressive and fatal, particularly in chronic fibrotic HP 4, 5

Prognostic Factors

Identification and complete avoidance of the inciting antigen is the most important prognostic factor—unidentified antigen is associated with increased risk of death (HR 2.43,95% CI 1.36-4.35) independent of fibrosis. 2

• Smoking is associated with poor prognosis and must be addressed as part of comprehensive management 1
• Fibrotic HP has significantly worse prognosis than non-fibrotic HP, with pulmonary fibrosis associated with 2.43-fold increased risk of death 2

When Diagnosis Remains Uncertain

If exposure history is unclear or CT findings are indeterminate, consider BAL fluid analysis (lymphocytosis ≥20%) and/or lung biopsy through multidisciplinary discussion to reduce diagnostic uncertainty before initiating treatment. 2

• BAL lymphocytosis alone does not rule in HP but provides additional support when combined with compatible CT findings and identified exposure 2
• Lung biopsy is unnecessary if definite HP diagnosis is unlikely to change management 2