Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)

Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) is a condition where the body produces too much of a hormone called antidiuretic hormone (ADH). This hormone controls how the kidneys manage water balance in the body. When there is too much ADH, the kidneys retain excess water, which dilutes the blood and lowers the level of sodium, an important mineral for nerve and muscle function. This imbalance can cause symptoms like headache, confusion, weakness, and in severe cases, seizures. The condition mainly affects the kidneys and the body's fluid balance system. It often occurs due to other illnesses or medications that disrupt normal hormone regulation.

Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) is characterized by excessive release of antidiuretic hormone (ADH) despite normal or low plasma osmolality, leading to impaired free water excretion and resultant hyponatremia. The core pathology involves inappropriate ADH secretion from the posterior pituitary or ectopic sources, commonly triggered by central nervous system disorders, malignancies (especially small cell lung carcinoma), pulmonary diseases, or certain drugs. This causes water retention, dilutional hyponatremia, and low serum osmolality with inappropriately concentrated urine. Clinically, SIADH is significant because it can cause neurological symptoms due to cerebral edema from hypotonicity. Diagnosis requires exclusion of other causes of hyponatremia such as hypovolemia, adrenal insufficiency, and hypothyroidism.