Background: Various etiologies of myomatous erythrocytosis syndrome (erythrocytosis associated with a uterine leiomyoma), one of which is altered production of erythropoietin, have been proposed. We report a case of erythrocytosis associated with a large uterine leiomyoma in which erythropoietin activity and immunostaining for erythropoietin in the leiomyoma were found. Case: A 64-year-old woman, gravida 2, para 1, was referred to our department for treatment of a large uterine myoma and erythrocytosis with elevated levels of erythropoietin. Total abdominal hysterectomy with bilateral salpingo-oophorectomy was performed, and the results of the pathological examination confirmed the diagnosis of leiomyoma of the uterus, which weighed 920 g. The patient’s postoperative course was satisfactory, and the levels of hemoglobin and erythropoietin were normalized and remained within normal ranges. The level of erythropoietin in the uterine leiomyoma measured by radioimmunoassay was elevated (372 mU/wet gram), and specific immunostaining for erythropoietin was found in the cytoplasm of leiomyoma cells. The levels of erythropoietin extracted from uterine leiomyomas of other patients who did not have erythrocytosis (control patients, n = 5) were lower (65 ± 15.3 mU/wet gram), but specific immunostaining for erythropoietin was also found in the cytoplasm of leiomyoma cells from those patients. Conclusions: Our case was typical of myomatous erythrocytosis syndrome in which uterine leiomyoma was proved to produce erythropoietin. Our results also suggest that erythropoietin is produced in uterine leiomyomas of patients with and without erythrocytosis. Leiomyoma of the uterus may affect the production of erythropoietin and may develop into myomatous erythrocytosis syndrome when the level of erythropoietin exceeds the normal range.

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