Endocrine Abstracts

A 31 year-old lady presented to clinic with an acute, three-week history of rapidly worsening polyuria and polydipsia. She described an eighteen month history of dysmenorrhoea with no galactorrhoea and reported no change in her vision. Her past medical history included alopecia areata one year previously from which she made a full recovery. Clinical examination was normal including full visual fields to red-pin confrontation. Biochemistry identified serum sodium of 141 mmol/l, serum osmolality 292 mOs/kg and urine osmolality 84 mOs/kg. On the basis of the history and these investigations she was diagnosed with diabetes insipidus, felt likely to be cranial due to the acuity of onset. She was started on DDAVP with good effect on her symptoms and this was titrated to a dose of 200 μg bd orally to achieve full control. Anterior pituitary function was normal (T4 of 14.5 pmol/l, TSH 4.1 mIU/l, 0900 h cortisol 238 nmol/l, LH 3.6 IU/l, FSH 4.1 IU/l, oestradiol 289 pmol/l, prolactin 383 mIU/l and testosterone 0.8 nmol/l). MRI scan of the pituitary showed a normal-size pituitary but without a posterior bright spot correlating with diabetes insipidus. There was diffuse thickening within the pituitary stalk, in keeping with an inflammatory process such as histiocytosis, sarcoid or infundibular hypophysitis. Epithelial tumour markers were checked in serum and CSF and were within normal limits. CSF was clear with low protein and normal glucose levels. Auto-antibody testing revealed a positive anti-smooth muscle antibody. Based on her history, biochemistry and imaging characteristics she was diagnosed with probable infundibular lymphocytic hypophysitis. Her symptoms have remained well controlled on oral DDAVP and interval imaging has shown no progressive hypothalamo-pituitary lesion. However, she developed secondary amenorrhoea with biochemical evidence of gonadotrophin insufficiency. She was started on transdermal oestrogen application and referred to the fertility service for assistance with conception. She conceived with gonadotrophin injections and with close endocrine input required an uptitration of her DDAVP during the early stages of pregnancy to account for extra thirst. Her pregnancy was uncomplicated and she delivered a healthy baby via caesarean section. Her periods have now returned, although irregularly, and her diabetes insipidus remains well controlled on 100 μg DDAVP qds. This is a case of acute onset cranial diabetes insipidus secondary to presumed lymphocytic infundibular hypophysitis. It highlights the diagnostic considerations in investigating this presentation as well as the management of DI in pregnancy.