Herbal medicine-induced multiple pulmonary pseudotumors

Japanese herbal medicines (HMs) cause adverse drug reactions (ADRs); however, solid nodule formation is uncommon. In this report, we aimed to show that ADRs with HM can mimic lung cancer. A 63-year-old man complained of back pain. His physician prescribed a traditional Japanese HM, Keishikajutsubuto, which alleviated his symptoms. After 4 weeks, a chest radiograph showed multiple lung nodules that were absent 6 months earlier; the patient did not have cough, fever, or dyspnea. Computed tomography (CT) showed multiple, bilateral lung nodules; however, blood tests and lung biopsy showed no abnormalities, ruling out interstitial pneumonia and lung cancer. Three months after the HM was discontinued, CT showed resolution of the lesions. Interstitial pneumonia was reported as a side effect of HM; however, no such side effect was reported for Keishikajutsubuto. When a patient presents with multiple lung nodules, a side effect of HM should be considered as a differential diagnosis.