Hyponatremia has occurred with a variety of medical conditions: adrenal insufficiency, congestive heart failure, hepatic cirrhosis, nephritic syndrome, hypothyroidism, psychogenic polydipsia, hyperglycemia, acute or chronic renal failure, vomiting, diarrhea and SIADH. It can be: hypovolemic, i.e., associated with sodium and water depletion; hypervolemic, i.e., associated with fluid overload and edema; or isovolemic, i.e., associated with normal or modest extracellular volume expansion. SIADH occurs with a variety of medical conditions: neoplasms (particularly carcinomas), CNS disorders (stroke, intracranial hemorrhage or hematoma, encephalitis or meningitis, or acute psychosis), or pulmonary disorders (pneumonia, tuberculosis, asthma, or chronic obstructive pulmonary disease). Hyponatremia and SIADH are associated with drugs such as CNS active drugs (e.g., tricyclic antidepressants), non-steroidal anti-inflammatory drugs and acetaminophen, thiazide diuretics and furosemide, sulfonylureas, angiotensin-converting enzyme inhibitors, and many anti-neoplastic agents. Hyponatremia usually defined as serum sodium < 135 mEq/L. If severe (serum sodium<120 mEq/L) or rapid, presenting signs and symptoms are suggestive of water intoxication. Cerebral edema symptoms: headache, mental confusion, disorientation, encephalopathy, tremors, gait disturbances, convulsions, and coma. Other symptoms: nausea, vomiting, and muscle weakness or cramps. Other laboratory abnormalities: decreased plasma osmolality, increased or decreased urine osmolality, and increased or decreased urine sodium concentration.