6-year-old with polyuria, weight loss and recent seizures (view video)
Patient will present as → a 25-year-old male complaining of a unabated thirst that began three weeks ago. He is constantly drinking and goes to the bathroom around five times a night. He has lost five pounds over the last few weeks. The patient is on lithium for a bipolar disorder. His BP is 115/70. The patient’s labs are significant for serum Na of 145 mEq/L (normal: 135-145). Urine osmolality is 185 mOsm/kg, and urine specific gravity is 1.004 (normal: 1.012 to 1.030).
Diabetes insipidus (DI) is caused by a deficiency of or resistance to vasopressin (ADH), which decreases the kidneys' ability to reabsorb water, resulting in massive polyuria
- Central diabetes insipidus (no ADH production most common type): idiopathic, autoimmune destruction of posterior pituitary from head trauma, brain tumor, infection, sarcoid
- Nephrogenic DI: partial or complete insensitivity to ADH: caused by drugs (Lithium, Amphoterrible), hypercalcemia and hypokalemia affect the kidneys ability to concentrate urine, acute tubular necrosis
Serum osmolality (concentration) is high (unable to stop secretion of water into the kidneys so blood becomes more concentrated) and urine osmolality is low because it is so dilute
The water deprivation test is the simplest and most reliable method for diagnosing CDI but should be done only while the patient is under constant supervision. Serious dehydration may result
- Normal response is progressive urine concentration
- Diabetes insipidus results in continued production of dilute urine despite water deprivation
Desmopressin (ADH) stimulation test: differentiates nephrogenic from central DI Give ADH
- Central DI - reduction in urine output indicating response to ADH
- Nephrogenic DI - continued production of dilute urine (no response to ADH) because kidneys can't respond
Central diabetes insipidus: Desmopressin/DDAVP (synthetic ADH)
Nephrogenic diabetes insipidus: Sodium and protein restriction - hydrochlorothiazide, indomethacin
diabetes mellitus type 1
central diabetes insipidus
nephrogenic diabetes insipidus
adverse drug reaction
discontinuation of lithium
substitution of carbamazepine for lithium carbonate
Water restriction can be used to distinguish central DI from primary polydipsia - however, in this situation, the clinical picture points toward central DI.
Loop diuretics are not used in the treatment of DI
CT scan of the brain
CT scan of the brain would likely reveal post-operative changes, but not help diagnose DI.
0.45% NaCl administered intravenously
Administration of fluids would not be sufficient for treatment of DI.