Whole-body Magnetic Resonance Imaging in Multiple Myeloma Made Easy

Purpose or Learning Objective: (1) Describe the pathologic spectrum of multiple myeloma (MM); (2) review the diagnostic criteria and its update including SLiM (S, 60% plasma cells; Li, light chains; and M, magnetic resonance imaging [MRI] lesions)-CRAB (hypercalcemia, renal dysfunction, anemia, bone disease) criteria; (3) review the imaging techniques; and (4) learn how to evaluate the treatment response.

Methods or Background: The disease spectrum of MM encompasses three main stages: monoclonal gammopathy of undetermined significance, smoldering MM, and MM itself. MM is diagnosed when end-organ damage is attributable to an underlying plasma cell proliferative disorder or when findings suggest a high likelihood of its development.

At imaging assessment, a finding of two or more ≥ 5-mm focal lesions seen at MRI is considered a myeloma biomarker. Bone disease is one of the most prominent features of MM and should be evaluated in all patients suspicious for MM.

Whole-body (WB)-MRI is considered the best technique to assess bone involvement, and extramedullary conditions can also be detected.

The Myeloma Response Assessment and Diagnosis System (MY-RADS) imaging recommendations have been proposed to standardize and reduce the number of variations in the acquisition, interpretation, and reporting of WB-MRI in myeloma and allow response assessment.

Results or Findings: Comprehensive protocols for WB-MRI include anatomical and functional imaging.

Basic sequences are whole-spine sagittal T1 and short tau inversion recovery (STIR), WB Dixon T1 axial or coronal, and WB diffusion. Additional sequences can be added, such as WB coronal STIR.

Due to the large set of images obtained, a protocolized method of study must be applied. We propose these four steps.

1. Diffusion: Most sensitive sequence to detect bone lesions but nonspecific. High b-values increase the lesion conspicuity, especially when inverting the gray scale.

2. Once detected, the lesion must be assessed in different morphological sequences, such as STIR and Dixon.

3. In a suspicious lesion, fat fraction maps must be obtained and measured from the Dixon images.

4. Quantitative values of the lesions must be measured on the apparent diffusion coefficient. These values are useful for lesion characterization and also for treatment response evaluation. At least two lesions of 5 mm must be present to establish the diagnosis.

Follow-up images should be obtained following the same protocol. Size, diffusion, and fat fraction measurements must be evaluated and compared with assessment response and fit into one of the five categories. We illustrate with examples of different lesions, response criteria, and pitfalls.

Conclusion: WB-MRI is the technique of choice for the diagnosis and follow-up of MM, and the MY-RADS system provides a comprehensive characterization of the myeloma state. Dixon and diffusion sequences are essential for bone evaluation. Radiologists must be aware of the advantages and limitations of each sequence, as well as follow-up recommendations.

Publication History

Article published online:
26 May 2023