Endocrine Abstracts

Isolated Central Diabetes Insipidus is a rare condition characterised by deficiency of arginine vasopressin (AVP) which presents with polyuria and polydipsia. The reported prevalence of diabetes insipidus is 1 in 25,000. The pathogenesis of central diabetes insipidus is often uncertain however the known causes can be divided into acquired, through trauma or vascular injury as well as infiltrative including malignancy, and congenital abnormalities which accounts for less than 10% of cases. Patients with this condition can often compensate through water consumption and therefore any disruption in their usual routine may lead to potentially fatal electrolyte disturbances. We present a 16 year old female patient who presented to the emergency department with increased water intake and lethargy. There was no previous medical history however it was reported that from the age of 3 years she had been obsessed with drinking water and the amount had steadily increased over the years where she was now consuming up to 15 litres per day. Her initial biochemistry was within the normal reference range (Sodium 144 mmol/l (133–146), potassium 4.1 mmol/l (3.5–5.3) and creatinine 51 umol/l (45–84)) and a provisional diagnosis of psychogenic polydipsia was made with paired osmolalities requested. She was limited to 4 l of fluid per day and following this her sodium level steadily increased over the subsequent 4 days to 156 mmol/l. The urine and serum osmolalities along with a water deprivation test revealed the diagnosis of central diabetes insipidus, the aetiology of which remains uncertain. MRI pituitary was performed measuring 5×7.5×13 mm, with normal stalk. She was commenced on desmopressin 100 mg three times per day and since has had no further polyuria, polydipsia or nocturia. A detailed history and physical examination can often unmask clues within the underlying aetiology and provide a timescale as to when the patient may have developed diabetes insipidus. Biochemical analysis and water deprivation test remain the gold standard for diagnosis. This case highlights the potential complications of misdiagnosis and treatment of patients with central diabetes insipidus. It is also important to identify the changes in fluid intake that can occur through concurrent illness which requires monitoring in these individuals and can often be challenging manage with adjustments in fluid balance and DDAVP dose required to prevent extreme electrolyte changes.