For SPB and extramedullary plasmacytoma the distinction is the presence of only one lesion (either in bone or soft tissue), normal bone marrow (<5% plasma cells), normal skeletal survey, absent or low paraprotein and no end organ damage.

Back pain and other consequences of the bone lesion may occur such as spinal cord compression or pathological fracture.

Around 85% of extramedullary plasmacytoma presents within the upper respiratory tract mucosa, causing possible symptoms such as epistaxis, rhinorrhoea and nasal obstruction.

[2] Bone marrow biopsies are performed to ensure the disease is localised; and in SPB or extramedullary plasmacytoma there will not be an increase of monoclonal plasma cells.

Tissue biopsies of SPB and extramedullary plasmacytoma are used to assess the phenotype of the plasma cells.

Histological analyses can be performed on these biopsies to see what cluster of differentiation (CD) markers are present and to assess monoclonality of the cells.

[4][5] An important distinction to be made is that a true plasmacytoma is present and not a systemic plasma cell disorder, such as multiple myeloma.

The difference between plasmacytoma and multiple myeloma is that plasmacytoma lacks increased blood calcium, decreased kidney function, too few red blood cells in the bloodstream, and multiple bone lesions (collectively termed CRAB).

[citation needed] Rarely, the Epstein–Barr virus (EBV) is associated with multiple myeloma and plasmacytomas, particularly in individuals who have an immunodeficiency due to e.g. HIV/AIDS, organ transplantation, or a chronic inflammatory condition such as rheumatoid arthritis.

[11] Radiotherapy is the main choice of treatment for both SPB and extramedullary plasmacytoma, and local control rates of >80% can be achieved.

Surgery is an option for extramedullary plasmacytoma, but for cosmetic reasons it is generally used when the lesion is not present within the head and neck region.

[12] Concerning that study,[12] a large prospective trial is needed to evaluate the impact of adding systemic anti-myeloma treatment to local radiotherapy.