Diabetes Insipidus (cont.)
Dipsogenic Diabetes Insipidus
A third type of diabetes insipidus is caused by a defect in or damage to
the thirst mechanism, which is located in the hypothalamus. This defect results
in an abnormal increase in thirst and fluid intake that suppresses ADH secretion
and increases urine output. Desmopressin or other drugs should not be used to
treat dipsogenic diabetes insipidus because they may decrease urine output but not thirst and
fluid intake. This fluid "overload" can lead to water intoxication, a condition
that lowers the concentration of sodium in the blood and can seriously damage the brain.
Gestational Diabetes Insipidus
A fourth type of diabetes insipidus occurs only during pregnancy. Gestational
diabetes insipidus occurs when an enzyme made by the placenta destroys ADH in the mother. The placenta is the system of blood vessels and other tissue that develops with the fetus. The placenta allows exchange of nutrients and waste products between mother and fetus.
Most cases of gestational diabetes insipidus can be treated with desmopressin. In rare cases, however, an abnormality in the thirst mechanism causes gestational
diabetes insipidus, and desmopressin should not be used.
Diagnosis of Diabetes Insipidus
Because diabetes mellitus is more common and because diabetes mellitus and
diabetes insipidus have similar symptoms, a health care provider may suspect that a patient with
diabetes insipidus has DM. But testing should make the diagnosis clear.
Your physician must determine which type of diabetes insipidus is involved before proper treatment can begin. Diagnosis is based on a series of tests, including urinalysis and a fluid deprivation test.
Urinalysis is the physical and chemical examination of urine. The urine of a person with
diabetes insipidus will be less concentrated. Therefore, the salt and waste concentrations are low, and the amount of water excreted is high. A physician evaluates the concentration of urine by measuring how many particles are in a kilogram of water (osmolality) or by comparing the weight of the urine to an equal volume of distilled water (specific gravity).
A fluid deprivation test helps determine whether diabetes insipidus is caused by (1) excessive intake of fluid, (2) a defect in ADH production, or (3) a defect in the kidneys' response to ADH. This test measures changes in body weight, urine output, and urine composition when fluids are withheld. Sometimes measuring blood levels of ADH during this test is also necessary.
In some patients, an MRI (magnetic resonance imaging) of the brain may be necessary as well.
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