Review Question - QID 104275

This patient's presentation of hyponatremia, history of small cell lung cancer, and urine/serum osmolality values is consistent with a diagnosis of syndrome of inappropriate secretion of antidiuretic hormone (SIADH). Initial treatment of SIADH is with water restriction.

There are numerous potential etiologies of SIADH; however, a commonly tested cause is the aberrant production of ADH by a primary or recurrent small cell lung cancer. Edema is typically absent in the clinical presentation of SIADH because, although volume expansion occurs due to water retention, edema is prevented from forming due to salt-wasting in the urine. Clinical manifestations of severe or overtly symptomatic SIADH, often neurologic due to swelling of brain cells, include altered mental status, seizures, coma, and even death. In the treatment of hyponatremia, there is always concern for precipitating central pontine myelinolysis by increasing serum Na levels too quickly; generally, the rise should not exceed 0.5 mEq/L per hour.

Incorrect Answers:
Answer 1: Demeclocycline inhibits the effect of ADH at the kidney; however, this measure is only indicated if hyponatremia becomes severe or profoundly symptomatic (typically below 120 mEq/L).
Answer 2: Desmopressin is indicated in the treatment of diabetes insipidus; it would likely worsen this patient's situation and further decrease serum Na levels.
Answer 4: Hypertonic saline is indicated in severe or significantly symptomatic cases of hyponatremia.
Answer 5: Lithium carbonate, much like demeclocycline, inhibits the effect of ADH at the kidney; however, this measure is rarely used and would only indicated if hyponatremia becomes severe or symptomatic.