Introduction: Hypersensitivity pneumonitis (HP) is an interstitial lung disease caused by an immune-mediated reaction of lung parenchyma to inhaled antigens. Lung function assessment is essential for evaluating disease progression and guiding management.

Objectives: To assess whether phenotype and early forced vital capacity (FVC) trajectory predict long-term progression in patients with HP.

Materials and Methods: This retrospective single-centre observational study included 82 patients. Spirometry (including %FVC predicted) and diffusing capacity for carbon monoxide (%DLCO predicted) were recorded at baseline, 1, and 5 years.
Patients were classified according to the change in FVC from baseline to 1 year as improvers (≥5%), stable (between −5% and +5%), or progressors (≤-5%). Patients were further classified according to radiological phenotype as fibrotic or non-fibrotic. Multivariable logistic regression analysis was performed to evaluate predictors of progression between years 1 and 5, including early FVC trajectory, phenotype, baseline FVC, and baseline DLCO.

Results: The cohort included 48 fibrotic and 34 non-fibrotic patients (mean age 67.4 years; 56.6% female). Early lung function trajectories were observed, with 39.5% of patients classified as progressors, 33.3% improvers, and 27.2% stable. 5-year progression was noted in a similar percentage of patients across different FVC trajectory groups, whereas progression occurred much more frequently in fibrotic than non-fibrotic phenotype (64.6% vs. 25.0%). (Tables 1 and 2)
In multivariable analysis, fibrotic phenotype was strongly associated with progression between years 1 and 5 (OR 0.09, p<0.001), whereas early FVC trajectory was not an independent predictor. Baseline lung function parameters were not significant predictors of progression. The overall model was statistically significant (p=0.003) and explained approximately 28% of the variance in the long-term outcome.

Conclusions: Patients with HP have heterogeneous clinical courses. Phenotype appears to be a more important determinant of long-term progression than short-term changes in lung function. Further research into predictive biomarkers is needed to improve risk stratification and better phenotype specific patient groups.