Diabetes insipidus (DI) Disorders of Neurohypophysis 

The neurohypophysis or posterior pituitary gland is made up of nerve tissues originating in su­praoptic and paraventricular nuclei of hypothala­mus.

• It produces 2 hormones:
• 1. AVP or arginine vasopressin, also known as antidiuretic hormone (ADH).
• 2. Oxytocin
• AVP acts on renal tubules to absorb the water back into the circulation helping to reduce the water loss and concentrating the urine.
• AVP deficiency causes diabetes insipidus.

Diabetes insipidus (DI) —

• It is a disease of ‘Posterior pituitary insufficiency or AVP deficiency in which large amounts of dilute urine are passed.
• inadequate secretion of or insensitivity to vasopressin (ADH) leading to hypotonic polyuria.
• In excessive AVP secretion, there is decreased urine output and hyponatraemia, especially if water intake is not reduced. This is called inappropriate ADH syndrome or inappropriate AVP production.
• In DI there is urine output more than 50 mljkg in 24 hours and osmolarity is <300 mosmol / L.
• There is polyuria, urinary frequency, nocturia, fatigue, .­somnolence (sleepiness), thirst, polydipsia.

Diabetes Insipidus Risk Factors

• Diabetes insipidus may be part of the paraneoplastic syndrome associated with small cell bronchocarcinoma.
• Intracranial neoplasm
• Patients using  lithium
• Following surgery
• Head trauma

Causes of Diabetes insipidus (DI) are:

• · Head trauma
• · Chronic meningitis
• · SLE (Systemic lupus erythematosus)
• · Snake venom
• · Craniopharyngioma
• · Pituitary adenoma
• · Metastatic tumors
• · Pregnancy
• · Sheehan’s syndrome (post partum pituitary apo­plexy)
• · Drugs like lithium, amphotericin B, aminoglycosides, rifampin
• Psychogenic Tubercular meningitis Multiple sclerosis

Diabetes insipidus (DI) Diagnosis —

• Initial Lab Tests

  • Plasma vasopressin or urinary vasopressin following osmotic stimulus, such as fluid restriction or administration of hypertonic saline
  • Urinary glucose: Rule out diabetes mellitus.
  • Normal:
    • Water restriction causes a rise in plasma osmolality and ADH secretion. This leads to water reabsorption in the collecting ducts. Urine is concentrated (urine osmolality >600 mosmol/kg)
  • Diabetes insipidus:
    • Lack of ADH activity means that urine is unable to be concentrated by the collecting ducts (urine osmolality <400 mosmol/kg).

• Blood test :

  • U&E and Ca²⁺ (Na⁺may be rise secondary to dehydration, K⁺ or Ca²⁺ as the aetiological factor). Plasma osmolality. Urine osmolality.

Treatment of Diabetes insipidus (DI)

• Treatment is DDAVP – a synthetic analog of AVP.
• It increases the urine concentration, and de­creases t~e urine flow.
• Other drugs are chlorpropamide (antidiabetic drug).
• Patient counselling helps in psychogenic poly­dipsia.
• Therapy depends on type of DI.
  • ›Orally available as 0.1- to 0.2-mg tablets
  • ›Intranasally 0.2–0.6 mg at bedtime
  • ›Desmopressin (DDAVP) a derivative of vasopressin, available PO, nasal spray, and parenterally
• Central DI:
  • ›Correct water deficits.
  • ›Reduce excessive urinary water loss.
• Symptomatic nephrogenic DI:
  • Amiloride can be added to HCTZ for the added effect.
  • Hydrochlorothiazide 25 mg once or twice a day
  • Thiazide diuretic with amiloride
• Contraindications Diabetes insipidus (DI):
  • Use desmopressin with caution in the immediate postop period for intracranial lesions because of possible cerebral edema.
• Precautions Diabetes insipidus (DI):
  • An overdose of desmopressin may produce water intoxication and hyponatremia in patients with excessive water intake.