Benign Metastasizing Leiomyoma With Myomatous Erythrocytosis Syndrome: First Reported Coexistence as a Unified...

Benign metastasizing leiomyoma (BML) is a rare condition characterized by histologically benign smooth muscle tumours arising at extrauterine sites, most commonly the lungs, in women with a history of uterine leiomyomata. Erythropoietin (EPO)-secreting uterine leiomyomata causing secondary erythrocytosis-termed myomatous erythrocytosis syndrome (MES)-is an exceedingly rare and underrecognized phenomenon first described by Thomson and Marson in 1953, with fewer than 70 cases reported to date. We report a 39-year-old woman who presented with incidentally discovered bilateral pulmonary nodules on imaging performed during workup for MES with markedly elevated serum EPO (26.7 mIU/mL). She had a longstanding history of uterine leiomyomata and endometriosis. CT-guided biopsy of the dominant left lower lobe nodule (14 × 11 mm) confirmed BML: lesional cells were positive for oestrogen receptor (ER), progesterone receptor (PR), smooth muscle actin (SMA) and desmin, with retained fumarate hydratase (FH), excluding hereditary leiomyomatosis and renal cell carcinoma (HLRCC) syndrome. Total hysterectomy with bilateral salpingo-oophorectomy (BSO) was performed; pathology confirmed multiple cellular leiomyomata without features of STUMP or leiomyosarcoma on University of Michigan expert consultation. Within 3 months of surgery, haemoglobin normalized to 14.2 g/dL and EPO to 6.7 mIU/mL, confirming the uterus as the source of ectopic EPO production. This case illustrates a novel unified hormonal syndrome in which uterine leiomyomata simultaneously drove pulmonary BML through ER/PR signalling and caused secondary polycythemia through ectopic EPO secretion. Hysterectomy/BSO resolved both processes concurrently, and this case highlights BML and MES as diagnoses to consider in premenopausal women with bilateral pulmonary nodules and unexplained erythrocytosis.