Hypersensitivity pneumonitis induced by spores of Lyophyllum aggregatum

Objectives: Lyophyllum aggregatum (LA) is called Shimeji in Japanese and is eaten commonly as a mushroom. Shimeji mushrooms are cultivated in an indoo r environment all year round. This study aimed to clarify the clinical feat ures of hypersensitivity pneumonitis (HP) induced by LA. Patients and setting: Ten patients showed mild respiratory symptoms includi ng dry cough, sputum, and low-grade fever. We tried to characterize the cli nical features and the findings using chest high-resolution CT (HRCT), pulm onary function tests (PFTs), and BAL fluid (BALF) tests in patients with HP induced by LA. HP was diagnosed from clinical features, HRCT findings, BAL F findings, lung histology, and lymphocyte stimulation tests (LSTs) for LA. Results: Laboratory findings showed mean (+/- SD) elevated levels of C-reac tive protein (0.78 +/- 1.3 mg/dL), erythrocyte sedimentation rate (48 +/- 2 3 mm/h), and gamma -globulin (26.9 +/- 7.6%). PFTs revealed a slight decrea se in the percentage diffusing capacity of the lung for carbon monoxide, po ssibly due to the presence of epithelial granulomas in the alveoli. Althoug h 4 of 10 patients showed normal findings on the chest radiograph (CSR), ch est HRCT findings of all patients showed centrilobular small nodules and di ffuse ground-glass opacities. The BALF testing revealed an increase in tota l cell counts, showing predominantly activated T lymphocytes. The CD4/CD8 c ell ratio was significantly decreased (0.5 +/- 0.3). The results of the LST s were positive in seven of seven cases. Conclusions: Since patients with HP induced by LA, typically have mild resp iratory symptoms and sometimes normal CXR findings, their conditions might remain undiagnosed. However, the chest HRCT images showed the typical subac ute phase of HP.