- Decreased production of ADH from the hypothalamus
- Results in inappropriately dilute urine
- Trauma or surgery affecting hypothalamic function
- Infiltrative or inflammatory process affecting hypothalamus (e.g. Sarcoidosis, Ig4 related disease, hypophysitis)
- Infection: encephalitis, meningitis
- Cancer: craniopharyngioma, Langerhan's histiocystosis, lymphoma, mets to hypothalamus/pituitary stalk
- Idiopathic; congenital
- May have symptoms related to the primary process (e.g. head trauma, cancer)
- From DI: persistent thirst, drinking large volumes of water, polyuria
- Degree of DI varies with amount of ADH produced
- If unable to drink enough free water to keep up with urine losses, may ultimately develop hypovolemia, confusion, hypernatremia
- Tachycardia, hypotension if volume depleted
- Altered mental status if significant hypernatremia
- + water deprivation test: continue to make large volumes of urine, with UOSM< Serum OSM despite no oral intake
- Low urine OSM, low specific gravity (ie persistently dilute urine)
- Elevated serum Osm and elevated serum sodium if can't keep up with urine losses of free water
- Situation corrects w/administration of DDAVP