Plasmacytoma

Solitary plasmacytoma of bone is one of many existing types of bone tumors and is part of the plasma cell disorder spectrum. It is a local clonal plasma cell proliferation without evidence of symptomatic multiple myeloma. It occurs slightly more frequently in males with a median age at diagnosis of 55 years. The thoracic vertebrae are most frequently involved. The exact etiology is unknown, although a role for acquired B-cell defects is suggested. In children and young adults, preceding trauma might play a role in the development of solitary plasmacytoma of bone. Compared to extramedullary plasmacytoma, solitary plasmacytoma of bone has a significantly worse prognosis, progressing to symptomatic multiple myeloma in over 50% of cases. The survival rates are significantly worse in case of abnormal serum immunoglobulin free light chain ratio, in patients diagnosed after the age of 60 years and in female patients. In one-third of presumed “solitary” plasmacytomas, an additional lesion is characterized with subsequent diagnostic imaging, marking the importance of further investigations when an apparent solitary plasmacytoma of bone is encountered. Conventional radiography plays a distinct role in the imaging and detection of solitary plasmacytoma of bone, mostly in the presence of clear clinical symptoms. It may show a “punched-out” lesion appearance with generally clear margins and normal surrounding bone. More advanced cases may be paired with marked erosion and cortical bone destruction, creating a “soap bubble” appearance. On CT, solitary plasmacytoma of bone presents as a uni- or multilocular lesion, causing focal trabecular destruction. A characteristic “mini brain” appearance may be observed. On conventional MRI, a plasmacytoma is iso- to hypointense on T1-weighted images and hyperintense on (fat-saturated) T2-weighted images compared to muscle and enhances homogeneously after gadolinium contrast administration. Specialized MRI techniques such as dynamic contrast-enhanced MRI and diffusion-weighted imaging also play an important role, especially in assessing disease extent and differentiation with multiple myeloma, where a focal solitary plasmacytoma of bone is accompanied by surrounding or distant bone marrow invasion. 18F-FDG PET/CT is useful in the evaluation and has a prognostic value both at diagnosis and in the evaluation of treatment.