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Excesses of other tropic hormones

Syndrome of inappropriate antidiuretic
hormone (SIADH)
SIADH results from an abnormal production or sustained
secretion of ADH and is characterize by fluid retention, serum
hypo osmolality, dilutional hyponateremia, hypochloremia,
concentrated urine in the presence of normal or increased
intravascular volume, and normal renal function. This
syndrome occurs more commonly in older adults.
Clinical manifestations
Excess ADH increases the permeability of the distal tubule
and collecting duct, which leads to the reabsorption of water
into the circulation. Consequently, extra cellular fluid volume
expands, plasma osmolality declines, the glamour filtration
rate increases, and sodium levels decline (dilutional
hyponatremia). Hyponatremia causes muscle cramps and
weakness. Initially, thirst, dyspnea on exertion, fatigue, and
dulled sensorium may be evident. The patient with SIADH will
experience low urinary out put and increased body weight. As
the serum sodium level falls, manifestations become more
severe and include vomiting, abdominal cramps, muscle
twitching, and seizures. As plasma osmolality and serum
sodium levels continue to decline, cerebral edema may occur,
Pathophysiology
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leading to lethargy, anorexia, confusion, headache, seizures,
and coma.