[Hypersensitivity pneumonia diagnosed by excisional lung biopsy: a clinicopathological features of 47 cases]

Objective: To analyze the clinicopathological and immunohistochemical characteristics of the hypersensitivity pneumonia (HP) cases that were diagnosed by excisional lung biopsy, to improve the diagnosis accuracy of HP. Methods: The data of 47 HP cases diagnosed by excisional lung biopsy during the last 20 years were collected in Peking Union Medical College Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, from January 2000 to June 2020. The clinicopathological features and the immunohistochemical profiles of CD3, CD4, CD8 and CD20 were analyzed using light microscopy and immunohistochemical stains. Results: The age of the patients ranged from 15 to 68 years, while the ratio of male to female was 22∶25. The main symptoms were shortness of breath and cough, and 32 cases had a history of allergen exposure. Most of the patients had restrictive impaired ventilatory function, and impaired diffusion function. The proportion of lymphocytes in bronchoalveolar lavage fluid (BALF) increased in 85.3%(29/34) of the patients, and the CD4⁺/CD8⁺ T cell ratio was not higher than 0.8 in 31.3%(10/32) of the patients. Microscopically, 59.6%(28/47) of the cases showed nonnecrotizing granuloma/giant cells in the stroma, and 40.4% (19/47) of the cases had only giant cells. Ninety-three-point six percent of the cases(44/47) had peribronchiolar metaplasia, while 70.2%(33/47) had focal cell-rich inflammation. Forty-four cases (93.6%, 44/47) had fibrosis, which was manifested as usual interstitial pneumonia-like fibrosis (47.7%, 21 cases), nonspecific interstitial pneumonia-like fibrosis (29.5%, 13 cases), purely peribronchiolar fibrosis (6.8%, 3 cases) and mixed fibrosis (15.9%, 7 cases). Immunohistochemistry showed that CD4⁺ T cells were fewer than CD8⁺ T cells in 24 cases (55.8%, 24/43) of HP. Thirty-two HP patients had follow-up data. Among them, 7 patients had improved symptoms, 12 patients were stable, and 13 patients had worsening symptoms. Conclusions: The most common type of HP diagnosed by excisional lung biopsy is chronic HP. The clinical characteristics are long course of disease, restricted ventilation disorder and impaired diffusion function with the increase of lymphocyte proportion in BALF. Nearly 1/3 of the patients have no known history of allergen contact. The degree of fibrosis in HP patients diagnosed by excisional lung biopsy is severe, and the histologic types of fibrosis varies, but the UIP-like and/or NSIP-like fibrosis is most common. The CD4⁺/CD8⁺ T cell ratio in lung tissues is less than 1 in more than half of the cases. Pulmonary fibrosis continued to increase in some of the patients with chronic HP, even after treatment.