Multiple myeloma (MM) is a diagnosis based on the presence of a monoclonal protein, plasmacytosis, and any one or more of the CRAB criteria including lytic lesions, renal insufficiency, anemia, and/or hypercalcemia.1 Until recently, the standard of care for the evaluation of MM-related bone disease had been whole-body x-ray (WBXR). The International Myeloma Working Group has revisited this definition very recently, incorporating, along with free light chain ratio and degree of marrow plasmacytosis, the presence of focal lesions on sensitive imaging techniques.2 In this recent consensus statement by Dr. Meletios Dimopoulos and colleagues, the International Myeloma Working Group (IMWG) has issued new evidence-based recommendations for the use of magnetic resonance imaging (MRI) for the evaluation of plasma cell disorders.
The consensus statement recommends the use of MRI to define symptomatic MM.3 This is now incorporated into the new definition of symptomatic MM.2 Evidence provided in the recent publication supports the conclusion that patients with lesions detected on MRI are at higher risk of progression to symptomatic MM4,5 and should be treated for MM. The statement further supports the use of MRI as the gold-standard method for the detection of bone marrow involvement by MM. MRI is also defined as the modality of choice to evaluate painful lesions, particularly in the axial skeleton, and to detect spinal cord compression. MRI is further recommended to distinguish between benign versus malignant MM-related osteoporotic vertebral fractures.
A solitary plasmacytoma of the bone (SBP) is defined by the presence of a solitary bone lesion in the absence of a clonal plasma cell population on bone marrow biopsy and lack of CRAB criteria. The majority of patients with this condition will ultimately progress and subsequently require systemic therapy for the treatment of MM. MRI is a more sensitive modality for the detection of occult lesions and is now recommended as part of the staging procedure in patients with SBP. The IMWG did not change its recommendation regarding the routine work-up of monoclonal gammopathy of undetermined significance and does not recommend MRI as part of the routine work-up. The authors of the consensus statement also highlight the role of MRI as a prognostic tool in the evaluation of MM but do not recommend the routine use of MRI for this purpose.
Historically, the use of MRI has been limited by cost, prolonged acquisition time, patient discomfort due to claustrophobia, and the exclusion of patients with metal devices. Whole-body MRI (WB-MRI), a method that does not require contrast, has been developed, circumventing or mitigating a number of these limitations. However, this technique is not widely available as of yet. The alternative to MRI when a more sensitive imaging modality is needed is positron emission tomography combined with computed tomography (PET-CT). Like, MRI, PET-CT is a more sensitive imaging modality than WBXR for the detection of active focal lesions.6 In one prospective study, PET-CT was inferior to MRI in the detection of diffuse pattern bone marrow involvement7 ; however, head-to-head, MRI was not found to be superior to PET in the detection of focal lesions in another.8
The IMWG consensus statement provides guidelines for the judicious use of MRI in the diagnostic evaluation of MM. The use of advanced skeletal imaging to better classify patients with asymptomatic MM and SBP will refine management of these diseases. Information gathered by such testing is practice-changing whereby a patient population at a high risk of progression is identified and considered for treatment. The use of WB-MRI, where available, is an excellent option with the added advantage of less radiation exposure.
Dr. Raje and Dr. O'Donnell indicated no relevant conflicts of interest.