Diabetes insipidus

Background

• Characterized as either:
  • Central Diabetes Insipidus (or neurogenic DI)
    • Deficient secretion of antidiuretic hormone (ADH)
  • Nephrogenic DI
    • Normal ADH secretion but decreased renal sensitivity to ADH
• Causes hypernatremia

Causes

• Central DI
  • Cancer
  • Pituitary surgery
  • Head trauma
  • Idiopathic
• Nephrogenic DI
  • Renal disease
  • Drug Induced (e.g Lithium)
  • Hypokalemia
  • Hypercalcemia
  • Polycystic kidney disease
  • Sjögren syndrome
  • Amyloidosis

Clinical Features

• Hypernatremia
• Decreased urine osmolality
• Dehydration
• Irritability
• Tremors
• Ataxia
• Hyperreflexia
• Spasms
• Seizures
• Death

Differential Diagnosis

Hypernatremia

Water loss:

• Decreased Intake
• Water loss > Na loss
  • Vomiting
  • Diarrhea
  • Sweating
  • Dialysis
  • Osmotic diuresis
• Central DI
  • Head Trauma
  • CVA
  • Tumor
  • Meningitis
• Nephrogenic DI
• Thyrotoxicosis

Sodium gain:

• Increased intake
  • Na intake
  • NaBicarb
  • Incorrect preparation of infant formula
• Renal Na retention (secondary to poor perfusion)

Evaluation

• Urine specific gravity < 1.010
• Measure serum and urine sodium while patient is water-deprived
  • Lack of response to water deprivation is diagnostic
  • Serum Osm >295 mOsm/L
• Record response to 5 units subcutaneous vasopressin
  • Response to vasopressin is diagnostic of central DI (response is indicated by urine osm >800 mOsm/L)
  • No response is diagnostic of nephrogenic DI
• In adults, onset of central DI usually abrupt whereas onset gradual in nephrogenic DI

Management

• Place foley for strict I/Os
• Volume repletion with normal saline or lactated ringers solution
• Patients will be water-deprived
  • Calculate water deficit: Water deficit (in Liters) = [(Body weight(kg)x0.6)x((Measured sodium/Normal sodium)-1)]
• Serum sodium should not decrease by more than 10-15 mEq/L per day in chronic cases of hypernatremia
  • Over-aggressive reduction of serum sodium may result in cerebral edema secondary to presence of idiogenic osmoles the build up in brain cells when exposed to chronic hypernatremia
  • If patient acutely hypernatremic, idiogenic osmoles have not had time to build up in brain tissue and rapid correction of hypernatremia would not develop cerebral edema

• Nephrogenic diabetes insipidus
  • Low-salt, low-protein diet
  • Hydrochlorothiazide 25mg BID
  • Indomethacin has greater effect at reducing urine output than ibuprofen

Disposition

• Admission for further workup and/or volume replacement
• Nephrology follow up

See Also

• Hypernatremia