Predictors of forced vital capacity response to immunosuppression in fibrotic hypersensitivity pneumonitis: a retrospective cohort analysis of 203 patients.

Background: Efficacy of targeted immunosuppression in fibrotic hypersensitivity pneumonitis (f-HP) remains uncertain due to a lack of controlled studies. We assessed predictors of acute treatment response to immunosuppression (3 to 9 months) in patients with either newly diagnosed or established progressive f-HP. Methods: Patients with f-HP who received corticosteroids (CS) and/or steroid-sparing agents (SSA) [mycophenolate mofetil or azathioprine (AZA)] with pulmonary function test (PFT) at baseline and three to six months after treatment initiation were included. An absolute increase in percent-predicted forced vital capacity (FVC%) of at least 5% within six months of treatment initiation was deemed a positive response. Logistic regression was used to identify baseline covariables associated with treatment response. Results: Among 203 treated patients, 29% had an acute response in FVC%. Male sex [adjusted odds ratio (OR) =0.36, 95% confidence interval (CI): 0.18-0.69, P=0.003], radiologic honeycombing (adjusted OR =0.37, 95% CI: 0.15-0.90, P=0.03), and higher baseline FVC% (adjusted OR =0.97, 95% CI: 0.95-0.99, P=0.01) were associated with reduced likelihoods of treatment response. Newly diagnosed patients had a greater likelihood of treatment response (adjusted OR =2.59, 95% CI: 1.35-5.09, P=0.005), while in established disease, only causative antigen identification was predictive of treatment response (adjusted OR =3.52, 95% CI: 1.15-10.73, P=0.03). Conclusions: Male sex, radiologic honeycombing, and higher FVC% at baseline were associated with lower odds of treatment response, while newly diagnosed and untreated patients were more likely to respond.