Diabates Insipidus
Body water and osmotic homeostasis are balanced by
❖ arginine vasopressin (AVP) signaling . by It is also known as antidiuretic hormone . produced in the hypothalamus and stored in the posterior pituitary
❖ serum osmolality .
❖ arterial blood volume
It activates the renal vasopressin2 receptor (V2R) at the basolateral membrane of principal cells in the distal convoluted tubule (DCT) and collecting duct. This increases tubular fluid permeability via insertion of water channel aquaporin 2 (AQP2) into the apical membrane. Reabsorption of water via increase in AQP2 channels
Central DI
Basic defect: deficient production and secretion of AVP
Nephrogenic DI
Basic defect: renal insensitivity to antidiuretic effect of AVP
Clinical Presentation · · · · ·
-
Polyuria
-
polydipsia
- incontinence, nocturia, and enuresis
- present with either: Hypovolemia and hypernatremia (if does not have an intact thirst mechanism ) Euvolemia and normonatremia (if patient has an intact thirst In neurosurgery cases, central DI may develop postoperatively! • infants: frequent heavy and wet diapers, irritability mechanism )
Diagnosis and Evaluation Steps to confirming the diagnosis:
• confirm true polyuria
• Exclude other causes of polyuria such a ❖ drugs and
❖ metabolic causes (hyperglycemia, hypokalemia)
• children >2 years:
· urine volume >40 ml/kg/day · urine osmolarity <300 mOsm/L, and
· negative glucosuria are diagnostic of DI
If diagnosis equivocal
- Water deprivation test ( desmopressin administration )
Central DI: urine osmolality (and an equivalent fall in urine output) will rise Nephrogenic DI: urine osmolality will not rise or will rise only minimally .
