[Significance of hyponatremia in patients with oropharyngeal tumors].

We observed 29 patients with hyponatremia associated with oropharyngeal carcinoma. In 19/29 the hyponatremia was attributable to a decreased effective arterial blood volume whereas in the remainder (10/29) the presence of SIADH could be demonstrated. These etiologies of hyponatremia were best differentiated by the plasma urea concentration (less than 30 mg/dl in SIADH), urate concentration (less than 4,0 mg/dl in SIADH) and creatinine concentration (less than 0,9 mg/dl in SIADH). Furthermore, SIADH patients had a spontaneous natriuresis. The mainstay of therapy in either form of hyponatremia is fluid restriction (less than 1 l/d).