Inappropriate Secretion of Antidiuretic Hormone in a Patient with Squamous Cell Carcinoma of the Lung mimicking Pulmonary Tuberculosis

A 71-year-old man with squamous cell carcinoma of lung mimicking pulmonary tuberculosis associated with the syndrome of inappropriate secretion of ADH(SIADH). Laboratory examination showed serum sodium concentration of 108 mEq/l. serum osmolality 247 mEg/l urine sodium concentration of 141 mEq/l urine osmolality 547 mEq/l. normal levels (<0.56 pg/ml) of serum antidiuretic hormone (ADH). ADH release was regulated normally with changes in serum osmolality. SIADH was diagnosed on the basis of hyponatremia with corresponding serum hypoosmolality and a high urine osmolality due to continuous sodium excretion. In this case, SIADH was probably induced by increased renal sensitivity to ADH and suspected high serum ANP level of unknown origin.