Antigen identification and avoidance on outcomes in fibrotic hypersensitivity pneumonitis

Background Suspected causative antigens may be unidentified in 30–50% of patients with fibrotic hypersensitivity pneumonitis (f-HP). It is unclear whether antigen identification and avoidance in this setting offer any additional clinical benefit. We hypothesised that antigen identification and avoidance may improve the clinical course of patients with fibrotic disease.

Methods Patients meeting recent international practice guidance for f-HP diagnosis evaluated at Mayo Clinic Rochester from January 2005 to December 2018 were included. Causative antigen and antigen avoidance were specifically defined and ascertained through review of the medical records. Cox proportional-hazards regression was performed to assess antigen identification and avoidance as predictors of either all-cause mortality or lung transplantation.

Results 377 patients were included. Of these, suspected causative antigen was identified in 225 (60%). Identification of a suspected antigen (adjusted hazard ratio (HR) 0.69, 95% CI 0.48–0.99; p=0.04) and subsequent antigen avoidance (adjusted HR 0.47, 95% CI 0.31–0.71; p<0.001) were associated with decreased all-cause mortality and transplantation. Both those with suspected antigen identification but nonavoidance and those with unidentifiable antigen had increased risk of all-cause mortality or transplantation (adjusted HR 2.22, 95% CI 1.34–3.69; p=0.002 versus adjusted HR 2.09, 95% CI 1.34–3.26; p=0.001, respectively). Exposure to avian antigen was associated with better outcome compared to other antigen subtypes (adjusted HR 0.63, 95% CI 0.43–0.93; p=0.02).

Conclusion Our findings suggest that antigen identification and antigen avoidance remain relevant even in patients with fibrotic disease, where both appear to be associated with improved outcomes.