The literature indicates that 30% of diabetes insipidus (DI) cases are idiopathic, 25% are related to malignant or benign tumors of the brain or pituitary, 16% are secondary to head trauma, and 20% follow cranial surgery.
Idiopathic DI is associated with destruction of cells in the hypothalamus, often as part of an autoimmune process. This is characterized by lymphocytic infiltration of the stalk and posterior pituitary. An MRI scan may show abnormalities in these structures. The presence of antibodies directed against vasopressin cells may help to predict the development of central DI.
The frequency with which DI develops after neurosurgery varies with the surgery's scope. Approximately 10-20% of patients experience DI following transsphenoidal removal of an adenoma, but the percentage of patients experiencing the condition postoperatively increases to 60-80% with large tumors. However, not all cases of DI are permanent. In a German study of metabolic disturbances after transsphenoidal pituitary adenoma surgery, only 8.7% of DI cases persisted for more than 3 months.
The most common causes of postoperative polyuria are excretion of excess fluid administered during surgery and an osmotic diuresis resulting from treatment for cerebral edema.
A prospective study in 436 patients who sustained severe head injury found that DI occurred in 15.4% of all such individuals.
Primary intracranial tumors causing DI include craniopharyngioma or pineal tumors. Appearance of other hypothalamic manifestations may be delayed for as long as 10 years. Thus, periodic follow-up of patients diagnosed with idiopathic DI is necessary to detect slowly growing intracranial lesions.
Familial DI is rare. Almost 90% of hereditary cases of nephrogenic DI result from an X-linked defect of the AVP receptor 2 gene (AVPR2).8 A rare autosomal dominant variant results from the mutation of AQP2, an aquaporin gene that gives rise to a water channel that is expressed exclusively in the kidney's collecting ducts. Autosomal dominant central DI that involves mutations of the AVP - neurophysin gene has also been identified. Mutations reported to date involve the signal peptide region or, more commonly, neurophysin II.9 The mechanism by which the mutations impair AVP release is not understood but may involve the accumulation of the ADH precursor, leading to the death of the ADH-producing cells.
Other causes of DI include cancer (eg, lung cancer, lymphoma, leukemia), hypoxic encephalopathy, infiltrative disorders (histiocytosis X, sarcoidosis), anorexia nervosa, and vascular lesions, such as arteriovenous malformations or aneurysms.