Endocrine Abstracts

A 34-year old female with type 1 diabetes presented to the antenatal clinic complaining of polydipsia, polyuria and nocturia. She was 12 weeks pregnant with adequate glycaemic control on a basal-bolus insulin regime. She reported new onset headaches but no deterioration in vision. On examination, her visual fields were full to confrontation with red pin. She was eunatraemic (Na 138 mmol/l), had an early morning cortisol of 332 nmol/l and normal thyroid function tests (FT4 16 pmol/l, TSH 1.73 munit/l). A formal water deprivation test was not undertaken due to the potential risk of significant dehydration to the pregnant mother. She was, therefore, commenced on oral Desmopressin for suspected diabetes insipidus, advised to drink to thirst and referred for a non-contrast pituitary MRI to exclude a mass lesion. This showed a slightly bulky pituitary gland with a visible posterior bright spot. Although her osmotic symptoms improved after starting Desmopressin, she was becoming disproportionately fatigued to the stage of pregnancy, necessitating a small dose of Hydrocortisone, with good symptomatic benefit. A provisional diagnosis of lymphocytic hypophysitis was made. Regular scans confirmed good fetal growth throughout the pregnancy and she subsequently delivered a healthy baby boy at term. Her pituitary function was reassessed post-partum. A pre-hydrocortisone cortisol level was satisfactory at 439 nmol/l and she reported no polydipsia or polyuria after omission of her Desmopressin. A repeat MRI pituitary showed a reduction in the size of the gland and basal pituitary function returned to normal, consistent with resolution of the hypophysitis. She was discharged from clinic on her pre-pregnancy doses of insulin and off all pituitary hormone replacement. She has recently, however, represented in the first trimester of her second pregnancy with polyuria and polydipsia and is currently undergoing assessment by her local endocrine team. Lymphocytic hypophysitis is well reported to occur in pregnant women, particularly when there is a history of autoimmunity, and may well be transient. Diabetes insipidus in pregnancy is associated with diagnostic challenges especially as standard dynamic pituitary function tests are unsafe. The diagnosis is, therefore, often presumptive and this case highlights the importance of close monitoring during pregnancy and early assessment of the pituitary axis post-partum.