Solitary Plasmacytoma of the Rib: A Report of a Rare Case

BACKGROUND Solitary plasmacytoma of bone (SPB) is a rare malignant plasma cell neoplasm, comprising 6% of all plasma cell tumors. It is characterized by a solitary osteolytic lesion. CASE REPORT This report describes an asymptomatic SPB in the rib of a 66-year-old man. X-ray and computed tomography (CT) initially showed localized bone resorption and destruction of the right fifth posterior rib, with a 4.0×2.4×2.8 cm soft-tissue mass. Single-photon emission computed tomography (SPECT) confirmed isolated rib involvement without multifocal skeletal lesions. Pathology and immunohistochemistry (CD138+, CD38+) confirmed the SPB diagnosis. SPB usually presents as a single osteolytic lesion, which often occurs in the vertebrae and skull. Rib involvement in SPB is uncommon, due to its nonspecific imaging features, often causing diagnostic delays or misdiagnosis. Radiotherapy is the primary treatment for localized SPB. However, there is a 30% to 50% risk of progression to multiple myeloma (MM), necessitating long-term surveillance of serum M protein and periodic imaging. CONCLUSIONS This case emphasizes that for adult patients with isolated rib destruction with or without the formation of soft-tissue masses, the possibility of SPB should not be ruled out, even in the absence of typical clinical symptoms and clear imaging and laboratory examination evidence. Multimodal imaging and immunohistochemical analysis are critical for accurate diagnosis. Early intervention and regular monitoring optimize outcomes and reduce misdiagnosis risks. Regular follow-up is vital to detect disease changes early and adjust treatment plans promptly.