[Hypernatremia due to hypothalamic tumor: ADH response to changes in plasma osmolality].

A case of a patient with the syndrome of chronic hypernatremia and hypodispia due to hypothalamic tumor was studied to evaluate the change of ADH response to plasma osmolality during the clinical course. A 23-year-old man was admitted for investigation of anorexia, hypodipsia and gait disturbance. Examination showed memory disturbance and generalized muscle weakness. Investigation showed marked hypernatremia (177 mEq/l) and hypopituitarism. Water loading test showed that ADH was not stimulated by hyperosmolality but continued to be secreted at a more or less constant level approximating normal basal state. CT scan revealed hypothalamic tumor. The tumor was suspected to be germinoma due to its radiosensitivity and high serum hCG level. After irradiation, the tumor lesion disappeared. ADH secretion came to be responsive to changes in osmolality but the response of the system was markedly reduced compared with the normal response, and hypodipsia and hypernatremia still remained. We conclude that the adipsia and complete destruction of the osmoreceptor in the patient caused marked hypernatremia and the destruction of ADH osmostat improved partially after irradiation. We believe it very useful for analyzing the disturbance of osmoregulatory system to evaluate the relationship of plasma ADH to plasma osmolality.