Diabetes insipidus

What is Diabetes insipidus?

Diabetes insipidus (DI) is a syndrome that is caused by the lack of the hormone vasopressin that is secreted by the posterior lobe of a pea-sized gland at the base of the brain (pituitary gland). Without vasopressin, the blood filtered by the kidneys (glomerular filtrate) cannot be reabsorbed by the kidneys to restore the blood volume. The water is then excreted in the urine. Diabetes insipidus can result from head trauma, brain tumors, infections like meningitis and encephalitis or vascular causes such as a stroke. There is also a rare inherited form of this disorder. Diabetes insipidus has no relationship with the more familiar disease, diabetes mellitus, a disorder of carbohydrate metabolism.

How is it diagnosed?

History: The individual will report excessive thirst, drinking large amounts of water (polydipsia), and urination (polyuria) especially frequent urination at night (nocturia). Other complaints may be fatigue, muscle weakness, constipation and dizziness.

Physical exam may be unremarkable in the cases where the fluid intake has kept up with the losses. When it has been in sufficient, for whatever reason, the physician may find a slow return of skin to original shape when gently pinched and released (poor turgidity), dry mucous membranes and a systolic blood pressure below 100 (hypotension). Other findings on exam may include a heart rate above 100 beats per minute (tachycardia), weak pulses in the arms and legs, cool, clammy skin and shallow but rapid respirations.

Tests: Urinalysis shows a low specific gravity and osmolality. The urine will be almost colorless. Two testing approaches can be used. One test involves giving an individual vasopressin to see if it changes the urine osmolality, and the second tests the kidneys with dehydration and then measures the vasopressin levels in the blood.

How is it treated?

Treatment consists of fluid replacement by close monitoring of the intake and output, specific gravity, and serum and urine osmolality. Vasopressin may be given in the form of nasal sprays.

Medications

Lozol (Indapamide), Tegretol (Carbamazepine)

What might complicate it?

Complications include dehydration, electrolyte imbalance and vascular collapse.

Predicted outcome

The treatment of diabetes insipidus is straightforward with a good prognosis. The underlying cause of the disorder may have different outcomes.

Alternatives

Other diagnoses may be diabetes mellitus, misuse of diuretics (water pills) or self over-hydration (psychogenic diabetes insipidus). There is a group of disorders that affect the kidneys' response to normal levels of vasopressin. This is called nephrogenic diabetes insipidus.

Appropriate specialists

Endocrinologist, urologist, neurologist, internist, and infectious disease specialist.

Last updated 13 November 2011