Inappropriate antidiuretic hormone secretion (IADHS) may occur in a variety of diseases, including malignancies, acute and chronic pulmonary diseases, central nervous system and endocrine disorders, acute psychosis, and surgical stress. It can be induced by drugs such as phenothiazines, cyclophosphamide, vincristine, thiazides, morphine, carbamazepine, and cisplatin. IADHS may accompany certain malignancies, particularly small-cell lung carcinoma, head/neck carcinomas, brain tumors, and lymphomas. The symptoms of IADHS syndrome include anorexia, nausea, headache, confusion, with the possible end result being coma. Laboratory findings include serum hyponatremia, elevated urinary sodium concentrations with normal renal and adrenal homeostasis. Few cases of prostate cancer associated with IADHS syndrome have been reported, and tumors were either poorly differentiated or small cell carcinoma and were almost uniformly metastatic at the time of diagnosis. Most of the patients died a few months after the diagnosis. In one case, elevated level of antidiuretic hormone was found in the patient's serum and in the prostatic tumor. The cytoplasm of the tumor cells was positive for prostate-specific antigen and was faintly positive for antidiuretic hormone (ADH). The patient responded well to combination therapy of androgen blockade with leuprorelin acetate and flutamide and subsequently laboratory findings of SIADH and serum ADH level returned to normal. However, he died of sudden profuse bleeding caused by gastric ulcers 6 months after the therapy (Sackset al. 1975; Gasparini et al. 1993; Yamazaki et al. 2001; Kawai et al.2003; Yalcin et al. 2000).
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