Endocrine Abstracts

JOINT491

Case: A 78-year-old woman presented with abnormal uterine bleeding. Endometrial biopsy revealed findings suggestive of a sarcoma. Upon there were no obvious signs of dehydration or edema. Without intravenous fluids, laboratory findings were as follows: serum Na 125 mEq/l, plasma vasopressin concentration 2.4 pg/mL, plasma osmolality 257 mOsm/kg, urine osmolality 354 mOsm/kg, urinary Na 101 mEq/l, plasma renin activity 0.6 ng/mL/hr, and serum uric acid 2.7 mg/dL. Given normal renal and adrenal cortical function, a diagnosis of syndrome of inappropriate antidiuresis (SIAD) was made. Fluid restriction was implemented along with intermittent administration of hypertonic saline. On hospital day 4, treatment was switched to oral NaCl, but even with NaCl administration of 12 g/day, serum Na did not increase sufficiently. Hypertonic saline was continued until serum Na reached 130 mEq/l. By hospital day 8, serum Na improved to 137 mEq/l, and a hysterectomy with bilateral salpingo-oophorectomy was performed while maintaining serum Na levels with a continuous infusion of approximately 1.5% hypertonic saline. Pathological examination revealed undifferentiated uterine sarcoma and endometrioid carcinoma. After surgery, hypertonic saline administration became unnecessary, plasma vasopressin concentration decreased to around 1.0 pg/mL, and serum Na stabilized in the 130 mEq/l range. The patient was discharged on oral NaCl 3 g/day. AVP immunostaining was performed on the tumor tissue, revealing AVP expression in some undifferentiated areas of the uterine sarcoma. AVP was not detected in the endometrioid carcinoma.

Discussion: Based on the clinical course and immunohistochemical findings, this case was considered SIAD caused by an ectopic vasopressin-producing tumor associated with uterine sarcoma. The causes of SIAD include central nervous system disorders, pulmonary diseases, ectopic vasopressin-producing tumors, and medications. Among ectopic vasopressin-producing tumors, small cell lung cancer is the most frequently reported and is well known for secreting AVP. The association between SIAD and gynecologic malignancies is rare. A literature search for cases of uterine sarcoma or endometrioid carcinoma associated with hyponatremia or SIAD identified only case reports of SIAD occurring during cisplatin-based treatment, with no other reported cases.

Conclusion: This case suggests a potential new etiology of SIAD associated with gynecologic malignancies and highlights its clinical significance.