Syndrome of inappropriate antidiuretic hormone secretion

Syndrome of inappropriate antidiuretic hormone secretion, known as SIADH or the syndrome of inappropriate antidiuresis, is a condition of physiologically inappropriate release of antidiuretic hormone, whether from the posterior pituitary gland or an ectopic source such as a lung tumor that secretes the hormone itself. Excessive antidiuretic hormone causes the kidneys to reabsorb too much solute-free water, producing hypotonic hyponatremia, a state of low plasma osmolality and reduced sodium concentration. It presents with loss of appetite, nausea, vomiting, abdominal discomfort, convulsions and, in severe cases, coma. Common causes span central nervous system disorders, malignancies such as small-cell lung cancer, medications including carbamazepine, cyclophosphamide and SSRIs, and pulmonary disease; in a substantial share of cases, between seventeen and sixty percent, no underlying cause is identified. Treatment addresses the root cause when one is found; otherwise management relies on fluid restriction, sodium supplementation, urea, intravenous saline or vasopressin receptor antagonists such as tolvaptan or conivaptan.