diabetes%20insipidus
DIABETES INSIPIDUS
Treatment Guideline Chart
Diabetes insipidus is a polyuric disease characterized by excretion of a large volume of hypotonic urine and hypernatremia. It is due to the absence of antidiuretic hormone.
Central (hypothalamic or neurohypophyseal) diabetes insipidus is the inability to secrete & produce vasopressin in the neurohypophyseal system. It is due to damage to the pituitary gland & hypothalamus, may be due to diseases, head injuries, neurosurgery, infection or genetic or autoimmune disorders.
In nephrogenic diabetes insipidus, there is inappropriate renal response to vasopressin. Kidney function may be impaired by drugs & by chronic disorders like polycystic kidney disease, sickle cell disease, kidney failure, partial ureteral block, hypokalemia, hypocalcemia, low protein diet & genetic disorders.
Primary polydipsia have abnormal increase in fluid intake.

Diabetes%20insipidus Diagnosis

Diagnosis

  • The diagnosis of DI requires osmotic stimulation of arginine vasopressin (AVP) secretion and measuring the adequacy of AVP secretion by either direct measurement of plasma AVP levels or indirect assessment of urine osmolality

History

Medical History and Physical Exam

  • History of head trauma or previous surgery, etc
  • Exclude possible mimics
    • DM
    • Intrinsic renal disease
  • Physical exam may be normal
    • Check for signs of dehydration and/or manifestations of hyperosmolality

Laboratory Tests

DI, by determining presence of true hypotonic polyuria, is suggested if both of the following are present:

  • Urine output >2.5-3 L/24 hr (>40 mL/kg/24 hr) in adults or >100 mL/kg/24 hr in infants
  • Urine osmolality <200 mosmol/kg or urine specific gravity <1.01 (when serum osmolality is >310 mosmol/kg)

Other lab tests should be performed:

  • Blood glucose, blood urea nitrogen (BUN), creatinine, serum electrolytes, urinalysis

Water Deprivation Test

  • Water deprivation should not be done if patient has severe fluid loss (eg >4.5 L urine/24 hr): Proceed directly to Desmopressin administration
  • Consists of closely observed 8-hour fluid fast
    • May be shortened to 4 hours for infants
  • Follow with administration of Desmopressin
  • Measure urine osmolality after fluid deprivation and after Desmopressin administration

Interpretation:

Urine Osmolality (mmol/kg) After Water Deprivation Urine Osmolality (mmol/kg) After Desmopressin Diagnosis
<300 <300 Nephrogenic DI
<300 >750 Central DI
>750 >750 Primary polydipsia
300-750 <750 Partial central DI, nephrogenic DI or primary polydipsia

Plasma Vasopressin Response to Increased Plasma Osmolality

  • This test is useful when fluid deprivation test is inconclusive
    • Used to confirm central DI
  • Increased plasma osmolality is induced by hypertonic 5% saline infusion given over 2 hours at 0.05 mL/kg/hr
    • Or until plasma osmolality of 300 mmol/kg is achieved
  • Not usually used in children due to limited availability of vasopressin assay and irritability to hypertonic saline administration

Measure Vasopressin After Period of Fluid Restriction

  • This test is useful when fluid deprivation test is inconclusive
    • Used to confirm nephrogenic DI
  • Urine osmolality and plasma vasopressin are measured after a period of fluid restriction
  • Not usually used in children due to limited availability of vasopressin assay

Trial of Low-Dose Desmopressin

  • This test is useful in younger children and when there is no facility to measure plasma vasopressin
  • Observe patient for ~4 days
    • Measure weight, plasma sodium (Na), urine volume and osmolality
  • Then give small doses SC or IM daily doses of Desmopressin for 7-10 days
    • Continue measurements
  • Central DI: Improvement, less thirst, decrease in urine output, Na normalizes
  • Nephrogenic DI: Thirst and polyuria persist
  • Primary polydipsia: Thirst persists and hyponatremia develops

Imaging

Brain Magnetic Resonance Imaging (MRI) 

  • Used to confirm the presence of structural lesion which is responsible for AVP deficiency in patients diagnosed with central DI
    • Classic finding on MRI is loss of posterior pituitary bright spot
    • Other common finding on MRI is thickening or enlargement of the pituitary stalk
    • Should be repeated after 6 months if findings are normal
  • In patients with primary polydipsia, MRI will show normal posterior pituitary bright spot and pituitary stalk
Editor's Recommendations
Special Reports