Hyponatremia

usually hypotonic and isovolemic (SIADH) or hypovolemic (CSW)

Syndrome of Inappropriate Antidiuretic Hormone Secretion

Water retention secondary to excess ADH secretion from neurohypophysis

Severe/acute SIADH signs: restlessness, irritability, confusion, seizure, coma

Treatment: fluid restriction, daily weights and lytes, avoid raising Na >10mEq/L/24hrs (risk of osmotic demyelination syndrome or central pontine demyelination)

Cerebral Salt Wasting Syndrome

Direct neural effect on renal tubular function

Hypovolemia due to Na⁺ loss in urine triggers ↑ ADH secretion (appropriate)

Treatment: fluid replacement and electrolyte correction

Diabetes Insipidus

deficiency of ADH; hyPERnatremia secondary to volume depletion

Fracture in/near the sella turcica may tear the stalk of the pituitary gland resulting in disruption of ADH secretion from the posterior pituitary

Signs: polyuria, excessive thirst, polydipsia

Treatment: DDAVP (analog of ADH)