Synchronous bone and adrenal extramedullary plasmacytoma: a rare case report and literature review

Abstract

BACKGROUND: Adrenal extramedullary plasmacytoma (EMP) is an exceptionally rare plasma cell neoplasm with fewer than 20 documented cases worldwide. The clinical presentation, optimal management strategies, and long-term outcomes remain poorly defined. CASE PRESENTATION: We report the case of a 51-year-old woman with synchronous bone and adrenal EMP, without multiple myeloma. The initial presentation involved pathological humeral fracture following minor trauma, with the subsequent discovery of a 40 mm left adrenal mass on staging CT. Emergency orthopedic fixation and bone biopsy confirmed the diagnosis of EMP. Immunohistochemical findings showed CD138, MUM1, and kappa light-chain restriction positivity, with negative lambda staining. After declining initial surgical intervention, the patient was lost to follow-up for two years, during which the adrenal lesion enlarged to 70 mm. Comprehensive staging including bone marrow biopsy, FDG-PET/CT, and laboratory workup confirmed absence of multiple myeloma features according to International Myeloma Working Group criteria. Complete laparoscopic left adrenalectomy was successfully performed, with uncomplicated recovery. Histopathological examination revealed a 75 × 55 × 30 mm encapsulated mass with characteristic plasma cell morphology and extensive hemorrhagic foci. The Ki-67 proliferation index was < 10% and Congo red staining was positive. Adjuvant lumbo-aortic radiotherapy (45 Gy) was administered. The patient achieved complete clinical and radiological responses at three-month follow-up. CONCLUSIONS: Synchronous EMP without multiple myeloma is an exceptionally rare entity that requires comprehensive systemic evaluation and multidisciplinary management. Contemporary management favors laparoscopic resection combined with adjuvant radiotherapy for optimal local control. Excellent survival outcomes support aggressive therapy, although lifelong surveillance remains essential given the potential progression to systemic disease.