Diabetes insipidus

Overview

This review by Christ-Crain and Gaisl, published in La Presse Médicale in 2021 as part of a series on pituitary disorders, covers diabetes insipidus (DI) with an emphasis on central DI. DI is defined by hypotonic urine output above 50 ml/kg per 24 hours with polydipsia above 3 litres a day. It is rare, with a prevalence of about 1 in 25,000, and men and women are equally affected.

Causes

Four groups of polyuria-polydipsia syndrome are described: central DI (deficient vasopressin production or release), nephrogenic DI (reduced kidney response), primary polydipsia (excessive fluid intake) and gestational DI. Central DI is usually acquired, for example after neurosurgery or head trauma, or from tumours, infiltrative or autoimmune disease and infections. Idiopathic cases are common, and hereditary forms are mostly autosomal dominant mutations of the AVP gene.

Diagnosis

Telling the forms apart is important because the wrong treatment can be dangerous. Desmopressin in a patient with primary polydipsia who keeps drinking can cause severe hyponatraemia. The classical water deprivation test has an overall accuracy of about 70%, and only about 41% in primary polydipsia. Copeptin, a stable marker of vasopressin, now gives better results. A baseline value above 21.4 pmol/L identifies nephrogenic DI, and copeptin after hypertonic saline stimulation (above 4.9 pmol/L) separated primary polydipsia from central DI with 96.5% accuracy. Arginine-stimulated copeptin is simpler and reached 93% accuracy. The pituitary bright spot on MRI is not reliable for diagnosis, but MRI is needed to look for structural causes.

Management

Central DI is treated with adequate fluids and desmopressin, dosed individually, and hyponatraemia is the main complication, so sodium and fluid intake need monitoring. In hospital, fluid balance is fragile and hypernatraemia must be corrected slowly. After pituitary surgery, DI may follow a triphasic course. Adipsic DI needs a fixed fluid prescription and regular sodium checks. The review also covers particular points in children.