Generality
Diabetes insipidus is a rare syndrome characterized by the conspicuous emission of urine, accompanied by an "insatiable thirst with preference for cold drinks. It is due to a lack or insufficient secretion of antidiuretic hormone (ADH or vasopressin) by the hypothalamus. and of the posterior pituitary, or its lack of activity in the kidney. In the first case we speak of central, ADH-sensitive or neurogenic diabetes insipidus, in the second of nephrogenic or ADH-insensitive diabetes insipidus (because it cannot be corrected by administering of exogenous vasopressin).
Signs and Symptoms
For further information: Symptoms Diabetes insipidus
Some patients with the disease manage to excrete up to 18 liters of urine per day. Under normal conditions, in fact, the vasopressin hormone acts in the last tract of the nephrons (distal tubules and collecting ducts), where it promotes the reabsorption of a considerable amount of water. In this way the volume of the urine is reduced and consequently their density (specific weight) increases. In the presence of an absolute or relative deficiency of vasopressin, polyuria is therefore an inevitable symptom, as are nocturia (the need to urinate several times during the night's rest) and polydipsia (abnormal thirst). See also: Diabetes Insipidus Symptoms
Diabetes insipidus is well tolerated as long as the patient has sufficient quantities of water available; if this does not happen or the patient is unable to drink, there is a rapid dehydration, with weight loss, haemoconcentration up to collapse and death.
Diagnosis
Laboratory tests show glucose concentrations in the urine and blood that are completely normal, which differentiates diabetes insipidus from diabetes mellitus (mellitus because the presence of glucose in the urine makes them as sweet as honey). On the other hand, hypernatremia and elevation of plasma osmolarity are recorded. As mentioned, the abundant urine shows low specific weight and osmolarity. The differential diagnosis between central and nephrogenic diabetes insipidus is based on the observation of the effects associated with the administration of exogenous ADH , which positively solves the first but not the second form.
Causes
There are numerous causes that can induce diabetes insipidus, both in its primary and secondary forms. At the base of this syndrome there may be, for example, rare genetic diseases or congenital malformations at the hypothalamic level (primitive forms); more frequently central diabetes insipidus is a consequence of head trauma, neurosurgery, infectious processes (encephalitis, meningitis) or intracranial tumors; however, in a good percentage of cases (30-40%) the cause remains unknown (idiopathic forms). Compared to the central one, nephrogenic diabetes insipidus is a very rare disease, sustained by the inability of the renal receptors to respond adequately to ADH, which is itself produced in normal quantities; also in this case there are congenital and acquired forms, including chronic renal insufficiency, hypercalcemia and hypokalaemia. Finally, there may also be transient forms, for example due to the action of substances that interfere with the action of "antidiuretic hormone.
Treatment
For further information: Drugs for the treatment of Diabetes Insipidus
The treatment of central diabetes insipidus consists in the administration of vasopressin by the nasal, oral or subcutaneous route, which allows the regression of symptomatic manifestations. In some and selected cases, the treatment can be etiological and as such be based on the removal of the promoting cause (eg removal of a tumor mass).
In the presence of nephrogenic diabetes there is no medical therapy and the disease is controlled by the intake of large quantities of water, restriction of sodium in the diet and the use of thiazide diuretics.
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