The syndrome of inappropriate antidiuretic hormone is characterized by the following:: (A) Hyponatremia and hyperkalemia, (B) Hypernatremia and hypokalemia, (C) Hyponatremia and urine sodium excretion >20 meq/1, (D) Hypernatremia and urine sodium excretion>20 meq/1
Answer is C. Syndrome of inappropriate antidiuretic hormone is caused by excess secretion of vasopressin leading to increased absorption of water resulting in hyponatremia, inappropriate sodium secretion in the urine (> 20 mEq/L), hyper osmolar urine (>100mOsm/L) and hypo osmolar plasma (<260mOsm/L). Ref: The MD Anderson Manual of Medical Oncology, 2nd Edition, CHAPTER 46