[A Case of Difficult-to-Diagnose Carcinomatous Meningitis Caused by Prostate Cancer Metastasis].

A 66-year-old man was referred to our hospital because of right leg pain. Computed tomography (CT) revealed multiple osteolytic changes. His serum prostate-specific antigen (PSA) level was increased to 77.83 ng/ml at the time of hospitalization. A prostate biopsy was performed, and histological examination results indicated poorly differentiated adenocarcinoma. Under the diagnosis of multiple bone metastasis of prostate cancer, androgen deprivation therapy was started. However, 1 month later, the patient was confused and lost appetite. Brain CT image demonstrated brain metastasis, and magnetic resonance image showed hydrocephalus. Although the patient underwent ventricular drainage because of a depressed level of consciousness, he died of primary disease complicated by pneumonia 3 months after the first visit. Perioperative cerebrospinal fluid cytological examination revealed adenocarcinoma cells. Therefore, a diagnosis of carcinomatous meningitis caused by prostate cancer metastasis was made.