Chronic hypersensitivity pneumonitis in Japan: a nationwide epidemiologic survey

Pulmonary fibrosis inevitably develops in patients with chronic hypersensitivity pneumonitis (HP).

We conducted a nationwide epidemiologic study in Japan to evaluate the frequency and clinical characteristics of chronic HP.

This report is on 36 cases of chronic HP, including 10 patients with summer-type HP, 5 patients with home-related HP, 7 patients with bird fancier's lung, 5 patients with isocyanate-induced HP, 4 patients with farmer's lung, and 5 patients with other types of chronic HP. Chronic HP was further subgrouped into 2 types: one type of patients were first seen with chronic disease (9 patients), and the other type became chronic with fibrosis after repeated acute episodes (27 patients).

The upper lung field was frequently involved in chronic HP (17%). Ground-glass opacities were observed in 57% and air space consolidation in 30% of the patients. Honeycombing was apparent in 37%. Twenty-six of 28 patients had antibodies to the presumptive antigens. Five of 8 patients with chronic HP were positive for antigen-induced lymphocyte proliferation. In 2 cases patients did not have detectable antibodies to causative antigens, although antigen-induced lymphocyte proliferation was detectable. The ratio of CD4 to CD8 in BAL lymphocytes was lowest in isocyanate-induced HP (mean 0.22) and tended to be high in farmer's lung and bird fancier's lung. Granulomas were observed in 39% and Masson bodies in 42% of specimens on histologic examination. Administration of prednisolone was effective in 58% of patients.

The insidious form of chronic HP has probably been misdiagnosed as idiopathic pulmonary fibrosis when a good history was not taken and immunologic (especially antigen-induced lymphocyte proliferation) and BAL testing were not counted.