Most Common Sites for Bone Lesions in Multiple Myeloma
The spine is the most frequently affected bone site in multiple myeloma, followed by the pelvis and ribs, with the axial skeleton being predominantly involved rather than the appendicular skeleton. 1, 2, 3
Anatomic Distribution Pattern
Axial Skeleton Predominance
- The distribution of osteolytic bone metastases in multiple myeloma is predominantly in the axial skeleton, particularly the spine, pelvis, and ribs, rather than the appendicular skeleton. 2
- Lesions in the proximal femur and humerus are not uncommon, though less frequent than axial involvement. 2
- The spine is the bone site most frequently affected by myeloma-induced osteoporosis, osteolyses, or compression fractures, occurring in almost 80% of newly diagnosed symptomatic patients. 3
Why the Axial Skeleton?
- This distribution pattern correlates with red bone marrow distribution, where slow blood flow possibly assists attachment of metastatic cells. 2
- The surface-to-volume ratio of trabecular bone (abundant in axial skeleton) is much higher than cortical bone, causing disease processes to occur more floridly in trabecular bone than at sites of cortical tissue. 2
Specific High-Risk Sites
Vertebral Involvement
- Spinal cord compression may occur in almost 20% of cases, requiring rapid diagnosis and treatment to avoid permanent sensory or motor deficits. 3
- Vertebral body collapse with significant neurologic complications is a major concern. 2
- The thoraco-lumbar spine is particularly vulnerable to purely lytic lesions and compression fractures. 4
Thoracic Cage
- The sternum and ribs are common sites where bone scintigraphy shows greater sensitivity than plain X-rays for detecting lesions. 4
- These thoracic lesions are often difficult to demonstrate by plain X-rays alone. 5
Clinical Implications of Site Distribution
Fracture Risk
- Pathologic fractures occur in both the axial and appendicular skeleton, with axial skeletal fractures of vertebral bodies being particularly concerning. 2
- The proximal long bones (femur and humerus) represent important sites for potential pathologic fractures despite being less commonly involved than axial sites. 2
Pain and Neurologic Complications
- Severe bone pain requiring radiation therapy or narcotic analgesics (or both) is common due to osteolytic skeletal destruction. 2
- Vertebral lesions can lead to spinal cord compression requiring urgent intervention. 3
Imaging Considerations by Site
Skull and Ribs
- Skull and rib lesions are not as well detected by WBLD-CT or MRI compared to conventional skeletal surveys, so focused X-rays may still be valuable when these areas are of clinical concern. 6, 7
- The characteristic skull finding is multiple "punched-out" osteolytic lesions with a "raindrop" or "Swiss cheese" appearance. 7
Spine Assessment
- MRI is presently considered the most appropriate diagnostic technique for evaluating vertebral alterations, as it detects both the exact morphology of lesions and the pattern of bone marrow infiltration. 3
- WBLD-CT is recommended as the standard procedure for detecting lytic disease overall, detecting up to 60% more relevant findings compared to conventional skeletal surveys. 6, 7