
Diagnosis Definition
- Multiple Myeloma (MM) is diffuse or multifocal involvement of hematologic tumors of plasma cell origin
- It most commonly occurs in males in their 60’s
- A single metastatic lesion of plasma cell origin is termed a plasmacytoma
- Predilection sites of MM are the ribs, sternum, scapula, skull, spine, pelvis, humerus, and femur
- Complications of MM include bone pain/fractures, frequent infections, reduced renal function, and anemia

Imaging Findings
- Bone scintigraphy is not useful to detect MM because the disease process inhibits osteoblastic activity
- Lytic bone lesions from MM can be difficult to see on radiographs or even CT scans
- MRI is the most sensitive and specific imaging method for the detection of bone marrow infiltration before mineralized bone has been destroyed
- PET/CT and whole-body MRI combined is more effective than either modality alone in detecting MM
- Patterns of bone marrow infiltration include normal appearing marrow, focal infiltration, diffuse disease, heterogeneous “salt-and-pepper” involvement, or combined focal and diffuse infiltration
- MRI typically shows lesions that are hypointense on T1-weighted images, hypointense to isointense on T2, and hyperintense on STIR
- The benefit of contrast use must be weighed against the risk of developing nephrogenic systemic fibrosis in patients with MM-associated renal failure

Pearls
- High signal within affected ribs on T2-weighted images with fat suppression is called the “white ribs sign”
- Decreased lesion size and a high signal peripheral halo of fatty marrow (aka “fatty halo sign”) on T1Â indicates treatment response
- The differential diagnosis of MM on MRI includes leukemia, lymphoma, and metastases
- Bone lesions often include cortical breakthrough and extension into the soft tissues; epidural extension can result in emergent cord compression

References
- Leucovet FE, Vande Berg BC, Malghem J, et al. Magnetic resonance and computed tomography imaging in multiple myeloma.  Semin Musculoskelet Radiol 2001; 5(1):43-55
- Hanrahan CJ, Christensen CR, Crim JR. Current concepts in the evaluation of multiple myeloma with MR imaging and FDG PET/CT.  RadioGraphics 2010; 30(1):127–142

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