Syndrome of inappropriate antidiuretic hormone secretion as an initial presentation of prostate cancer

We report a patient with the syndrome of inappropriate antidiuretic hormone secretion (SIADH), viral meningitis, and prostate cancer. After resolution of the viral meningitis, hyponatremia presented. Following a radical prostatectomy, however, the hyponatremia resolved without any therapy that would increase serum sodium. Although SIADH may be present in any type of carcinoma, its frequency in prostate cancer is low. The diagnosis of SIADH in prostate cancer may indicate a poor prognosis.