A case of transient hyperthyroidism induced by placental site trophoblastic tumor.

We report a case of placental site trophoblastic tumor (PSTT) with transient hyperthyroidism. A 29-year-old gravida 2 para 2 woman presented with abnormal genital bleeding 6 months after delivery. Endometrial histology suggested PSTT. Serum human chorionic gonadotropin (hCG) was 117 mIU/mL and serum estradiol (E2) were 51 pg/mL. She reported increased appetite, sweating, fatigue, and 7-kg weight loss within 3 months. Blood samples showed a thyroid-stimulating hormone (TSH) level <0.01 μIU/mL, FT3: 24.3 pg/mL, FT4: 5.3 ng/mL. The patient was diagnosed with hyperthyroidism. After thyroid function normalized, laparoscopic hysterectomy and bilateral salpingectomy were performed. Two years postsurgery, there was no recurrence, and thyroid function improved. The hCG produced from gestational trophoblastic disease has stronger TSH activity than that from gestational trophoblasts. However, in PSTT, the E2 level, which increases thyroid-binding proteins and suppresses elevated thyroid hormone levels, is low and may induce hyperthyroidism. In cases of suspected PSTT, thyroid function should be evaluated when hyperthyroid symptoms are present.