Synchronous extradural dorsal spinal extramedullary plasmacytoma and invasive urothelial carcinoma of the bladder: a rare dual primary malignancy

Abstract Background Multiple primary malignancies (MPMs) are defined as two or more histologically distinct primary neoplasms occurring in the same individual, either simultaneously or sequentially. Synchronous presentation of two unrelated malignancies is uncommon and poses important diagnostic and therapeutic challenges. Extramedullary plasmacytoma (EMP) accounts for less than 5% of plasma cell neoplasms, whereas urothelial carcinoma is the most common malignancy of the urinary tract. Synchronous occurrence of EMP and urothelial carcinoma is exceedingly uncommon, with only isolated cases reported in the literature. Case presentation We report a 74-year-old man who presented with progressive lower-limb weakness and painless hematuria. Magnetic resonance imaging demonstrated an extradural dorsal spinal mass, while contrast-enhanced computed tomography revealed an enhancing bladder lesion. Histopathological and immunohistochemical examination confirmed a kappa-restricted extramedullary plasmacytoma of the dorsal spine and an invasive high-grade papillary urothelial carcinoma of the bladder. Bone marrow examination together with systemic myeloma work-up excluded plasma cell myeloma. Both lesions were managed according to their respective standard treatment protocols. Conclusion This case highlights the importance of independently evaluating anatomically distinct lesions to establish synchronous primary malignancies requiring separate staging and management. Although a shared biological mechanism cannot be established from a single case, reporting such uncommon presentations contributes to the clinicopathological literature and may facilitate recognition of similar cases.