Endocrine Abstracts

Introduction: We present two pregnant women who were referred to obstetric endocrinology service with polyuria and polydipsia. They were investigated and treated for diabetes insipidus (DI). In both cases, the underlying pathophysiology was ADH insufficiency secondary to autoimmune lymphocytic hypophysitis. There are currently no consensus guidelines on the diagnosis of DI during pregnancy. These cases highlight best practice and endorse MDT management of chronic hypopituitarism.

Cases: Patient 1 was referred at fifteen weeks gestation with excessive thirst and polydipsia. She had a background of autoimmune lymphocytic hypopysitis (aged 16) diagnosed after resection of a presumed pituitary macroadenoma. She had been well off endocrine replacement in the interim 14 years but remained amenorrhoeic (she declined HRT). She conceived with IVF and became symptomatic with D.I. at 5 weeks’ gestation. She had a water deprivation test during her pregnancy and outside of pregnancy, the result would have been normal. She was treated with dDAVP, stopping after delivery. Patient 2 was also referred at twenty weeks’ gestation with thirst (drinking twenty litres/day) and nocturia. Her symptoms had started during a previous pregnancy two years previously, which ended in miscarriage. In her second pregnancy the symptoms became much worse. A random serum/ urine osmolality showed 310 mosmol/ kg and 37 mosmol/kg respectively. A non-contrast MRI showed symmetrical enlargement of the pituitary stalk, suggestive of autoimmune lymphocytic hypophysitis. She was treated with dDDAVP with prompt resolution of her symptoms and remains on treatment.

Discussion: Cranial DI is a state of increased thirst and water loss due to deficient ADH secretion. The diagnosis is complicated by physiological changes during pregnancy. Pregnancy is a state of fluid retention, mediated by changes in water homeostasis; pregnant women feel thirst at lower serum osmolarities and pass higher volumes of urine. Both of our patients had a primary deficiency of ADH to due lymphocytic hypophysitis. In one of the patients, the damage was subclinical and unmasked by pregnancy. In pregnancy the vasopressinase activity of placental cystine aminopeptidases leads to a 3-4 fold increase in ADH catabolism. Their pituitary glands were unable to meet this increased demand. Differential diagnosis is HELLP syndrome / liver impairment. This was ruled out in our patients. Our patients were treated successfully with desmopressin, which is safe in pregnancy and required regular monitoring for water intoxication and hyponatremia. dDAVP is more resistant to placental vasopressinases than endogenous ADH.