Syndrome of inappropriate antidiuretic hormone
Excessive release of antidiuretic hormone (ADH) disturbs fluid and electrolyte balance in syndrome of inappropriate antidiuretic hormone secretion (SIADH). The excessive ADH causes an inability to excrete dilute urine, retention of free water, expansion of extracellular fluid volume, and hyponatremia.
SIADH occurs secondary to diseases that affect the osmoreceptors (supraoptic nucleus) of the hypothalamus. The prognosis depends on the underlying disorder and response to treatment.
Causes
The most common cause of SIADH is small cell carcinoma of the lung, which secretes excessive levels of ADH or vasopressin-like substances. Other neoplastic diseases—such as pancreatic and prostatic cancer, Hodgkin’s disease, and thymoma—may also trigger SIADH.
Less common causes include:
central nervous system disorders
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