A Case of Syndrome of Inappropriate Secretion of Antidiuretic Hormone Due to an Oat Cell Lung Cancer with High Plasma Levels of Atrial Natriuretic Hormone

Abstract

A case associated with syndrome of inappropriate secretion of antidiuretic hormone (SIADH)due to an oat cell carcinoma of the lung with high plasma atrial natriuretic peptide (ANP) levels was reported. The patient was admitted with cough and fever. Laboratory data showed serum hyponatremia (114mEq/l) associated with serum hypoos-molality(233mOsm/l)and high plasma levels of ANP(157pg/ml, normal range <10pg/ ml). Because of the absence of dehydration and normal renal function a diagnosis of SIADH was made. Findings of the Carter-Robbins test with a Swan-Gantz catheter suggested that ANP was not released from the tumor, but that it might be from cardiac muscles. Treatment with multimodality therapy resulted in improvement of hyponatremia with reduction of the tumor. A high concentration of ADH and very low concentration of ANP was detected in the resected tumor extract. It is suggested from this result that the mechanism of hyponatremia in cases of SIADH is as follows ‘. (1) inappropriate secretion of ADH, (2) increase of circulating blood volume, (3) increase of atrial pressure, (4) ANP secretion, (5) powerful natriuretic effect. © 1991, The Japan Lung Cancer Society. All rights reserved.