Endocrine Abstracts

A 24 year old student was referred from her GP in 2022 with a one month history of polyuria and polydipsia, drinking up to 15 litres of water a day. Renal function, serum glucose and Hba1c were unremarkable but urinalysis showed a specific gravity 1.010. On further questioning her symptoms had progressively worsened over the past 6 months and reported weight gain of 6 kg in 6 months and intermittent headaches but regular menstrual cycles. She had no past medical history of note and was not taking any regular medications nor supplements. Initial biochemistry showed a sodium 147 mmol/l, potassium 4.2 mmol/l, normal renal function with a GFR >90, pituitary profile was within normal limits and serum osmolality was 297 mosmol/kg with a urine osmolality of 75 mosmol/kg. Water deprivation test was consistent with a diagnosis of cranial diabetes insipidus and she was subsequently started on desmopressin with a good clinical response. Pituitary imaging showed a thickened infundibulum contacting the undersurface of the optic chiasm without compression. The pituitary gland was normal in size and shape with no focal lesions. Subsequent interval MRI showed stable appearances and posterior pituitary bright spot demonstrated. Given the unchangeable appearances on pituitary imaging, further investigation into the aetiology of diabetes inspidius is being sought. So far, pelvic imaging has been carried out consistent with polycystic morphology of the right ovary and skeletal survey is unremarkable. She is currently awaiting a PET scan and discussions with the local pituitary MDT are ongoing. Diabetes insipidus or arginine vasopressin deficiency is a rare condition affecting 1 in 25,000 people. It is caused by a reduced production of or failure to respond to anti-diuretic hormone (ADH) resulting in polyuria and polydipsia¹. Most causes of cranial diabetes insipidus are due to trauma, neurosurgery or pituitary tumours with more rare causes including infiltrative disease, infections, genetic defects or are idiopathic^2,3. A diagnosis of diabetes insipidus in a young person can be difficult given lifelong medication, potential side effects and regular contact with hospital services. This case demonstrates a clear diagnosis and clinical response to treatment but the cause remains unclear.