Description

• Disorder in which large volumes of dilute urine are excreted (polyuria) as an inappropriate response to antidiuretic hormone, arginine vasopressin (AVP)
• Polyuria defined as >3 L in 24 hr
• Often characterized by excessive fluid intake (polydipsia)
• 2 types:
  • Central diabetes insipidus (DI, CDI; failure or deficiency of AVP release):
    • 4 types:
      • No AVP to release (loss or malfunction of posterior pituitary neurons)
      • Defective osmoreceptors – release AVP only in response to severe dehydration
      • Elevated threshold for AVP release
      • Subnormal amount of AVP released
    • Familial cases have been reported (autosomal dominant)
  • Nephrogenic DI (lack of renal response to AVP):
    • Differentiate from primary polydipsia
    • Some cases are X-linked recessive in males
• Must be distinguished from primary polydipsia caused by either psychiatric disorder or abnormal thirst

Etiology

• Central DI:
  • Any condition that disrupts the osmoreceptor–hypothalamus–hypophyseal axis:
  • Highest incident in ages 10–20 yr:
    • Trauma (skull fractures, hemorrhage)
    • Pituitary or hypothalamic surgery
    • CNS neoplasm: DI can be considered a tumor marker:
      • Pituitary adenomas
      • Craniopharyngiomas
      • Germinomas
      • Pinealomas
      • Meningiomas
    • Metastatic tumors:
      • Leukemia/lymphoma
    • Granulomatous:
      • Histiocytosis
      • Sarcoidosis
    • Congenital CNS defects
    • CNS infections (e.g., meningitis, encephalitis)
    • Pregnancy (Sheehan syndrome)
    • Idiopathic (autoantibodies, occult tumor)
    • Wolfram syndrome (DI, DM, optic atrophy, deafness)
    • Ethanol
• Nephrogenic DI:
  • Any condition that impairs the kidney's response to AVP:
    • Congenital renal disorders
    • Obstructive uropathy
    • Renal dysplasia
    • Polycystic kidney disease
    • Systemic disease with renal involvement
    • Sickle cell disease
    • Sarcoidosis
    • Amyloidosis
    • Drugs:
      • Lithium (most common and persists past discontinuation of drug)
      • Amphotericin
      • Phenytoin
      • Aminoglycosides
      • Methoxyflurane
      • Demeclocycline
    • Electrolyte disorders:
      • Hypercalcemia
      • Hypokalemia

• Typically presents in the second trimester:
  • Unclear etiology, but likely increased production of vasopressinase by the placenta
  • Leads to a decrease in AVP and transient DI
  • Watch patient closely during anesthesia and periods of water restriction
  • Typically clears after 2–6 wk after delivery
  • Can treat with desmopressin (DDAVP), which resists this additional vasopressinase
• Sheehan syndrome may cause DI