Diabetes Insipidus (DI)
meduploader - 06-29-09 15:25

Deficient ADH action resulting in copious amounts of extremely dilute urine. Subtypes are as follows:
Central DI: Caused by destruction or dysfunction of the posterior pituitary by neurosurgery, infection, tumors, cysts, hypophysectomy, histiocytosis X, granulomatous disease, vascular disruption, autoimmune disease, trauma, or genetic diseases.
Nephrogenic DI: Caused by chronic renal disease, congenital factors, hypercalcemia, hypokalemia, and lithium.
Polyuria, polydipsia.
The hallmark is inappropriately dilute urine in the setting of elevated serum osmolality (urine osmolality < serum osmolality).
Hypernatremia occurs if the patient lacks access to free water or does not have an intact thirst mechanism.
Psychogenic polydipsia—polyuria due to &#8593; drinking, usually > 5 L of water per day, leading to dilution of extracellular fluid and water diuresis.

DIAGNOSIS
Plasma and urine osmolality.
Water deprivation test: If serum osmolality is not elevated, consider this test, in which the patient is denied access to water, and serum and plasma osmolalities are checked frequently until serum osmolality is elevated.
Urine specific gravity < 1.005 or urine osmolality < 200 mOsm/L indicates DI.
A rise in urine osmolality > plasma osmolality indicates psychogenic polydipsia.
DDAVP test (synthetic vasopressin): Once the diagnosis of DI is established, perform to distinguish central from nephrogenic DI.
TREATMENT
Central DI: DDAVP administration (IV, SQ, PO, or intranasally).
Nephrogenic DI: Treat the underlying disorder if possible. Thiazide diuretics and amiloride may be helpful.
COMPLICATIONS
Hypernatremia, hydronephrosis.