SIADH

Definition

The syndrome of inappropriate antidiuretic hormone hypersecretion (SIADH) is a condition mostly found in patients diagnosed with small cell lung cancer, pneumonia, brain tumors, head trauma, strokes, meningitis, and encephalitis. This is a syndrome characterized by excessive release of antidiuretic hormone (ADH or vasopressin) from the posterior pituitary gland or another source. The result is hyponatremia, and sometimes fluid overload. The normal function of ADH on the kidneys is to control the amount of water reabsorbed by kidney nephrons. ADH acts in the distal portion of the renal tubule (Distal convoluted tubule) as well as on the collecting duct and causes the retention of water, but not solute. Hence, ADH activity effectively dilutes the blood (decreasing the concentrations of solutes such as sodium). As a background, serum sodium concentration is regulated by the balance of water intake, renal filtration, and reabsorption of sodium, and antidiuretic hormone (ADH) –...