MANIFESTATION OF SUBCLINICAL DIABETES-INSIPIDUS DUE TO PITUITARY-TUMOR DURING PREGNANCY

We describe a case of diabetes insipidus (DI) due to a pituitary tumor in a 33-year-old pregnant woman who developed a sudden onset of polyu ria (over 8 l/day) and polydipsia at 30 weeks of gestation. Her plasma concentration of vasopressin (AVP) was low compared with high serum o smolality (298 mOsm/kg), and her urine output was well controlled by t reatment with desmopressin acetate (DDAVP). Cranial magnetic resonance imaging (MRI) demonstrated a 1.8 x 1.2-cm pituitary tumor, but she di d not have any disturbance in the release of anterior pituitary hormon es. The serum concentration of cystine aminopeptidase (CAP) was within the normal range for a woman at 34 weeks of gestation. After an uncom plicated delivery of a healthy girl, her polyuria gradually resolved. The size of the pituitary tumor gradually decreased in parallel to a r eduction in her urine output, but a silent hemorrhage was detected in her pituitary gland 4 weeks after the delivery. Although pregnancy is sometimes associated with central DI, the occurrence of DI due to pitu itary tumor under pregnancy is rare. The basal AVP recovered to within the normal range, but the low response of AVP secretion to high osmol ality persisted. In this case, pregnancy may affect the manifestation of subclinical DI. This case may therefore enhance our understanding o f the mechanisms of DI during pregnancy.