The most common cause of diabetes insipidus is the failure of vasopressin secretion in response to normal physiologic stimuli (pituitary or neurogenic diabetes insipidus). A less common cause is failure of the kidneys to respond to vasopressin (congenital nephrogenic diabetes insipidus).

Two types of pituitary diabetes insipidus exist: primary and secondary. The primary form affects about 50% of patients. Familial or idiopathic in origin, this form may occur in neonates as a result of congenital malformation of the central nervous system (CNS), infection, trauma, or tumor.

The secondary form results from intracranial neoplastic or metastatic lesions, hypophysectomy or other types of neurosurgery, a skull fracture, or head trauma—which damages the neurohypophyseal structures. This form of the disease can also result from infection, granulomatous disease, and vascular lesions.

A transient form of diabetes insipidus also occurs during pregnancy, usually after the 5th or 6th month of gestation. The condition usually reverses spontaneously after delivery.

Untreated diabetes insipidus can produce hypovolemia, hyperosmolality, circulatory collapse, unconsciousness, and CNS damage. These complications are most likely to occur if the patient has an impaired (or absent) thirst mechanism.

A prolonged increase in urine flow may produce chronic complications, such as bladder distention, enlarged calyces, hydroureter, and hydronephrosis. Complications may result from underlying conditions, such as metastatic brain lesions, head trauma, and infections.

The patient’s history shows an abrupt onset of extreme polyuria (usually 4 to
16L/day of dilute urine, but sometimes as much as 30 L/day), extreme thirst, and consumption of extraordinary volumes of fluid. The patient may report weight loss, dizziness, weakness, constipation, slight to moderate nocturia and, in severe cases, fatigue from inadequate rest caused by frequent voiding and excessive thirst.

Physical examination may reveal evidence of dehydration, such as dry skin and mucous membranes, fever, poor skin turgor, and decreased muscle strength. Urine is pale and voluminous. Dyspnea, tachycardia, and hypotension may be evident.

To distinguish diabetes insipidus from other types of polyuria, the physician may order the following tests: