Abstract
Acute Sheehan syndrome is a rare condition that occurs hours to days post partum and causes hypopituitarism. It may cause hyponatremia due to adrenal insufficiency, and most patients improve with steroid therapy. However, hyponatremia is caused not only by adrenal insufficiency but also by inappropriate secretion of arginine vasopressin (AVP). We report the case of a 30-year-old Japanese primipara with massive postpartum hemorrhage and acute Sheehan syndrome. Hyponatremia developed following hypernatremia soon after the postpartum period; however, it did not improve despite adequate hydrocortisone supplementation. AVP fluctuated based on water balance and magnetic resonance imaging findings, showing distinctive AVP secretion dynamics. Oral 1-desamino-8-D-arginine vasopressin was temporarily needed during the clinical course, after which it was not needed, suggesting that impaired blood flow to the posterior pituitary lobe and its improvement may have contributed to the distinctive AVP secretion dynamics. Therefore, when hyponatremia is not improved despite adequate hydrocortisone supplementation in patients with acute Sheehan syndrome, the syndrome of inappropriate antidiuretic hormone secretion should be considered because distinctive AVP secretion dynamics can occur after severe ischemia of the pituitary gland.