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Diabetes Insipidus

Although most people would have heard of diabetes mellitus or 'sugar diabetes' few would have come across the condition called diabetes insipidus, a completely different and unrelated condition.

A disorder of water metabolism, diabetes insipidus results from a deficiency of circulating vasopressin (also called antidiuretic hormone) or from renal resistance to this hormone. Pituitary diabetes insipidus is caused by deficiency of vasopressin, whereas nephrogenic diabetes insipidus is caused by renal tubular resistance to the action of vasopressin. Diabetes insipidus is characterized by excessive fluid intake and hypotonic polyuria.

The disorder may start in childhood or early adulthood (median age of onset is 21) and is more common in men than in women. Incidence is slightly higher today than in the past.

In uncomplicated diabetes insipidus, the prognosis is good with adequate water replacement, and patients usually lead normal lives.

Causes

Two things cause diabetes insipidus. In some people, a part of the brain (called the hypothalamus) doesn't make enough antidiuretic hormone (called ADH), which your body needs to work right. In other people, the kidneys don't work with this hormone the way they should. Most people with diabetes insipidus get it after an injury to the head or after brain surgery. Some people with diabetes insipidus have a brain tumor. Sometimes it runs in families. Some medicines, like lithium, can also cause it. About 25% of the time, doctors can't find any reason for it.

Signs and symptoms

The patient's history typically shows an abrupt onset of extreme polyuria (usually 4 to 16 L/day of dilute urine, but sometimes as much as 30 L/day). As a result, the patient is extremely thirsty and drinks great quantities of water to compensate for the body's water loss. This disorder may also result in nocturia.

If the patient is unable to obtain adequate quantities of water, features of diabetes insipidus include signs and symptoms of dehydration (poor tissue turgor, dry mucous membranes, constipation, muscle weakness, dizziness, and hypotension). Polyuria usually begins abruptly, commonly appearing within 1 to 2 days after a basal skull fracture, a cerebrovascular accident, or surgery.

Relieving cerebral edema or increased intracranial pressure may cause all of these symptoms to subside just as rapidly as they began.

Diagnosis

• Urinalysis
• Urine output:
  • Central DI -- urine output suppressed by a dose of ADH
  • Nephrogenic DI -- urine output not suppressed by a dose of ADH
• MRI of the head

Treatment

Until the cause of diabetes insipidus can be identified and eliminated, administration of various forms of vasopressin can control fluid balance and prevent dehydration.

Vasopressin injection

This aqueous preparation is administered S.C. or I.M. several times a day because it's effective for only 2 to 6 hours. This form of the drug is used as a diagnostic agent and, rarely, in acute disease.

Desmopressin acetate

This drug can be given orally, by nasal spray that's absorbed through the mucous membranes, or by S.C. or l.V. injection. Desmopressin acetate is effective for 8 to 20 hours, depending on the dosage.

Prevention

There is no known prevention for diabetes insipidus . Treatment of causative disorders may prevent some cases of acquired nephrogenic DI . Medications should only be used under the supervision of the health care provider .