Is Plasmacytoma A Multiple Myeloma?

Plasmacytoma and multiple myeloma are both types of plasma cell dyscrasias. In plasmacytoma, there is a localized growth of abnormal plasma cells. In multiple myeloma, the abnormal growth of neoplastic plasma cells is not localized, but more widespread and systemic. Although, plasmacytoma and multiple myeloma have some similar characteristics, they are considered two different entities.⁽¹⁾

The diagnostic criteria for plasmacytoma includes, a biopsy revealing a solitary tumor inside a bone or tissue consisting of abnormal plasma cells. X-rays, PET scans or MRIs do not show any other skeletal bony lesions or soft tissue lesions. There is no evidence of myeloma in bone marrow biopsy. Blood tests are normal for anemia, serum hypercalcemia, and renal insufficiency due to M proteins.

The diagnostic criteria for multiple myeloma includes, plasma cell proliferation of around 10% of all the cells in the bone marrow, excessive production of M proteins, anemia (with Hb value <10 g/dl), hypercalcemia (serum calcium levels ≥11.5 mg/dl), renal insufficiency (serum creatinine >1.72 mmol/l) and bony lesions (with lytic lesions, severe osteopenia or pathologic fractures). The CRAB (high calcium, renal failure, anemia and bony lesions) pattern is consistent with multiple myeloma.

Plasmacytoma can be further divided into two distinct types, namely, solitary bone plasmacytoma and solitary extramedullary plasmacytoma. Solitary bone plasmacytoma is a lesion of the bone whereas solitary extramedullary plasmacytoma is a lesion of soft tissue. Plasmacytoma bone is the more common type than the plasmacytoma extramedullary type. Although, both the types can progress to multiple myeloma, plasmacytoma bone has >60% chance than plasmacytoma extramedullary, which has <30% to progress into myeloma.⁽²⁾

Although, both plasmacytoma and multiple myeloma are diseases of the elderly, plasmacytoma is found in relatively younger adults than multiple myeloma, more so, the extramedullary type. The median age of diagnosis of plasmacytoma is around 55-60 years, whereas, for multiple myeloma it is approximately 70 years. Plasmacytoma also has a relatively male predominance when compared to multiple myeloma. Male predominance was also greater for extramedullary type than bone plasmacytoma. Both multiple myeloma and plasmacytoma are common in the Black population.

The survival rate for both multiple myeloma and plasmacytoma is better when diagnosed at a younger age. However, survival rate for plasmacytoma is better than for multiple myeloma and better yet for plasmacytoma extramedullary than plasmacytoma bone. The survival rate for women is better than males in multiple myeloma, whereas, in plasmacytoma no such gender predilection has been noted. The prognosis of multiple myeloma has improved in the recent decade, whereas no such difference has been noted for plasmacytoma. This could be attributed to advancement in the management of multiple myeloma.

Therefore, despite, some similarities between the two diseases, both being plasma cell dyscrasias, they are two different entities. Plasmacytoma is not multiple myeloma, but an entirely different disease. The median time of progression to multiple myeloma is 2-3 years for plasmacytoma.

The diagnosis of plasmacytoma includes whole body X-rays of skeleton, bone marrow biopsy and blood tests to rule out full organ damage. However, recently researchers are of the opinion that the patients of plasmacytoma should also undergo MRI spine/FDG-PET, serum FLC ratio, immunoglobulin levels and MFC for the early diagnosis of cases that progress to multiple myeloma as early diagnosis of multiple myeloma will reduce mortality and morbidity and improve the prognosis and survival rate of the patients.

The management of multiple myeloma is extensive with the use of chemotherapy, radiation therapy, stem cell transplant and adjunctive surgical care. While radiotherapy is the first line treatment of plasmacytoma, and the role of chemotherapy, surgical therapy and combination therapy are still questionable.

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