Key points in Diabetes Insipidus´ Diagnosis

Abstract

Diabetes insipidus is mainly characterized by polyuria, urinary volume over 3 L/day or 40mL/kg/day in adults, leading to subsequent polydipsia; these features are also present in most cases of diabetes mellitus. We report the case of a 56-year-old man initially misdiagnosed with and treated for diabetes mellitus; he was eventually diagnosed with central diabetes insipidus following further laboratory tests. We have also conducted a thorough review of the literature relating to the physiology, diagnosis, and treatment of diabetes insipidus. The patient, who complained of polyuria, polydipsia and weight loss, and had fasting glucose levels of 108 mg/dL, was already using metformin to treat type 2 diabetes. He then developed hypoglycemic symptoms, and pre-and postprandial capillary glycaemia between 70 and 120 mg/dL, as a result of which metformin was suspended. Nevertheless, polyuria and polydipsia persisted. Based on a plasma osmolality of 305,5 mOsm/kg, urinary density of 1005 g/mL and low arginine vasopressin levels, a diagnosis of central diabetes insipidus was made and treatment with desmopressin was initiated. Because the symptoms of centraldiabetes insipidus and uncontrolled type 2 diabetes mellitus overlap, it is important to consider clinical presentations carefully in order to make a differential diagnosis.