Working group keys in on 3 criteria
The International Myeloma Working Group has agreed on 3 simplified criteria for diagnosis of symptomatic multiple myeloma.3 These include the presence of (1) clonal bone marrow plasma cells or plasmacytoma, (2) an M-protein in serum of unspecified concentration, and (3) tissue- or organ-related impairment, such as renal insufficiency or anemia.
Our patient easily met all 3. His bone marrow biopsy displayed 90% plasma cell cellularity. Additionally, his SPEP exhibited markedly increased IgG immunoglobulin, and immunofixation data suggested IgG type kappa monoclonal gammopathy. These findings, in combination with our patient’s blood chemistry abnormalities, marked proteinuria, and imaging findings, confirmed the diagnosis of multiple myeloma.
Rule out MGUS
The differential diagnosis for multiple myeloma includes monoclonal gammopathy of undetermined significance (MGUS). The characteristic findings of MGUS include:
- absence of symptoms,
- M-protein component (either IgG, IgA, or IgM) <3 g/dL,
- <10% plasma cells in the marrow,
- absence of lytic lesions, and
- no signs of anemia, hypercalcemia, or renal insufficiency.
Essentially, MGUS is a milder form of myeloma with a more indolent course. However, MGUS does carry a 1% annual risk of progression to frank myeloma. An additional concern for patients with multiple myeloma is progression to plasma cell leukemia (PCL). The prognosis for PCL is poor, and the diagnosis is made when the absolute plasma cell count exceeds 2000/mcL. The rate of occurrence of PCL as a progression of multiple myeloma is 1% to 4%.4
In addition to MGUS, the differential diagnosis for multiple myeloma includes tuberculosis, sarcoidosis, and metastatic disease.