Endocrine Abstracts

Case History: A 47-year-old man presented to his GP in November 2019 with sudden onset polydipsia, polyuria and large volume nocturia, passing approximately 5L of urine daily. He was drinking to thirst, had no past medical or family history, and was not taking any medication. He had normal serum calcium, sodium and HbA1c. His GP referred to the local endocrinologist. Five months later, he was referred to our tertiary centre for a water deprivation test, as it had not been possible for this to be performed locally.

Investigations, Results and Treatments: The patient was seen in our centre within 2 days of referral. Plasma and urine osmolalities, obtained five months earlier by the GP, were diagnostic of diabetes insipidus (DI): serum sodium 145 mmol/l, plasma osmolality 300 mOsmol/kg, urine osmolality 115 mOsmol/kg. Anterior pituitary function was normal other than secondary hypothyroidism. MRI of the pituitary and skull base CT demonstrated an aggressive destructive skull base process, significant paranasal sinus disease and poor dentition. Oral desmopressin 100 mg am and 200 mg nightly was commenced the same day (without performing a water deprivation test), with immediate improvement and the first full night’s sleep in six months. CT of the chest, abdomen, and pelvis; autoimmune and vasculitis screen; immunoglobulin-G subclasses, and Quantiferon tests were all normal. Regional Pituitary MDT case review that week could not ascertain clear aetiology. ENT review advised a 2-week course of co-amoxiclav and fluconazole, then subsequent endoscopic sinus surgery and biopsy, after negative SARS-CoV-2 PCR. During surgery, the sinuses opacified on imaging were clear and overtly normal. Biopsy showed lymphocytes and plasma cells, but no granuloma or neoplasia, and no bacterial, mycobacterial or fungal growth. Repeat imaging 3 and 6 months later showed a significant improvement in the skull base changes. DI however remained, fully controlled with normal sleep and normal serum sodium, except profound aquaresis on delayed desmopressin administration.

Conclusions and points for discussion: 1) Cranial DI diagnosis does not require a water deprivation test when the history and baseline biochemistry are diagnostic; 2) Prompt diagnosis of DI prevents prolonged symptoms, and ensures appropriate and timely investigation and management; 3) Early referral to a pituitary centre is important, greatly facilitated in the post-COVID era by almost universal adoption of virtual MDT meetings. the delay could have caused significant morbidity; 4) This case illustrates an unusual, probably infective, aetiology and the importance of expeditious management in all presenting patients.