Histopathological spectrum of hypersensitivity pneumonitis with clinico-radiologic correlation

There is no consensus on the classification of the diagnostic certainty of hypersensitivity pneumonitis (HP) based on the histopathological findings. This retrospective study aimed to describe the clinical and histopathological spectrum of HP. Herein, we also propose different grades of diagnostic certainty. Based on the histology, the cases were classified as: 'definite HP', 'probable HP', and 'possible HP'. Of the 47 subjects screened, 30 cases of histologically diagnosed HP (mean age 48.4 years; 50% women) were included. The findings of cellular bronchiolitis, interstitial pneumonia, interstitial granuloma, isolated interstitial multinucleated giant cells (MNGCs), airspace granulomas, isolated airspace MNGCs, and organizing pneumonia were present in 96.7%, 80%, 46.7%, 50%, 10%, 63.3%, and 16.7% cases, respectively. Based on the various combinations of histopathological findings, the cases were classified as 'definite', 'probable', and 'possible' HP in 56.7%, 33.3%, and 10%, respectively. Chronic HP was diagnosed in 56.7% cases based on the presence of fibrosis on histopathology. The histopathological diagnosis of subacute or chronic HP did not corroborate with the disease duration, and 17.6% of the subjects with duration of symptoms of <6 months had evidence of fibrotic disease on histopathology.