Occupational Asthma Reference

Petnak T, Thongprayoon C, Baqir M, Ryu JH, Moua T, Antigen identification and avoidance on outcomes in fibrotic hypersensitivity pneumonitis, Eur Respir J, 2022;60:2101336,10.1183/13993003.01336-2021

Keywords: HP, prognosis, fibrotic, birds, exposure avoidance, USA

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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.

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.

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).

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.

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This retrospective study of fibrotic hypersensitivity pneumonitis from the Mayo clinic shows that allergen avoidance was associated with improved transplant-free survival, which was still relatively poor (Median survival was 8.39 years for patients with identifiable causative antigen compared to 5.93 years for those with unidentifiable causative antigen). Prognosis did not improve for the first 3 years of follow-up, but after that allergen avoidance improved prognosis in the group whose causative agent had been found. If allergen avoidance was not successful the prognosis was as bad as those without an identified cause. This paper provides good evidence for allergen identification and avoidance in fibrotic disease, this had not been well shown before.

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