Leptomeningeal carcinomatosis in small cell carcinoma of the prostate

Introduction Leptomeningeal carcinomatosis in small cell carcinoma of the prostate is rare. Case presentation A 69‐year‐old man visited our hospital due to dysuria and edema. Bilateral hydronephrosis and lymph node metastases due to a pelvic tumor were observed. Although the prostate‐specific antigen level was normal, the tumor was suspected to originate from the prostate. He underwent percutaneous nephrostomy and prostate biopsy. Histopathology revealed small cell carcinoma accompanied by increased pro‐gastrin‐releasing peptide and neuron‐specific enolase levels. After receiving systemic chemotherapy with carboplatin and etoposide and radiation therapy for prostate, these lesions gradually decreased in size, and tumor markers normalized. Ten months after the initial diagnosis, he developed consciousness disorder and seizure. Magnetic resonance imaging revealed leptomeningeal carcinomatosis without any other recurrences and elevated tumor markers. He died 4 weeks after these symptoms appeared. Conclusion Careful monitoring of the central nervous system should be considered in small cell carcinoma of the prostate patients.