Why Multiple Myeloma Impacts the Lumbar Spine
Multiple myeloma preferentially affects the lumbar spine because this region contains abundant red bone marrow with high trabecular bone content and slow blood flow, creating an ideal microenvironment for myeloma cell attachment and osteoclastic bone destruction. 1
Anatomical and Pathophysiological Basis
The distribution of myeloma bone lesions follows the pattern of red bone marrow distribution, predominantly affecting the axial skeleton—particularly the spine, pelvis, and ribs—rather than the appendicular skeleton. 1 This phenomenon, known as osteotropism, reflects the extraordinary affinity of myeloma cells for bone marrow-rich areas. 1
Key Mechanisms of Spinal Involvement
Trabecular bone predominance: The surface-to-volume ratio of trabecular bone is substantially higher than cortical bone, causing disease processes to occur more floridly in trabecular-rich areas like vertebral bodies. 1
Vascular dynamics: Slow blood flow in the red bone marrow of vertebral bodies facilitates attachment of circulating myeloma cells to the bone marrow microenvironment. 1
Cytokine-mediated bone destruction: Neoplastic plasma cells produce interleukin-6, interleukin-1, tumor necrosis factor, and RANK-ligand, which are potent bone-resorbing factors that stimulate osteoclastogenesis while inhibiting osteoblasts. 2 This leads to progressive bone loss and development of osteolytic lesions. 2
Clinical Significance and Detection
The lumbar spine is the most frequently affected bone site in multiple myeloma, with bone disease observed in almost 80% of newly diagnosed symptomatic patients. 3
Diagnostic Superiority of MRI
MRI is the gold standard for detecting spinal involvement in multiple myeloma, demonstrating marked superiority over plain radiography and bone scintigraphy. 4 In one study examining 192 vertebrae from 18 patients, MRI detected 41 foci with abnormal signal intensity, while X-rays showed osteolytic lesions in only 4 vertebral bodies and bone scanning was positive in just 2 cases. 4
Screening recommendations: Plain radiography of the lumbar spine was positive in only 15 of 41 patients, while MRI detected lesions in 28 patients. 5 MRI of the lumbar spine is essential for patients with normal radiographs, as it can detect early marrow infiltration before cortical bone destruction occurs. 5
MRI patterns: On T1-weighted images, myeloma lesions typically show decreased signal intensity compared to normal marrow, while T2-weighted images demonstrate increased signal intensity in 53% of cases with focal disease. 6 Focal abnormalities are better visualized on T2-weighted sequences in 65% of patients with identifiable focal disease. 6
Clinical Monitoring
Baseline assessment: MRI of the spine should be performed in patients with monoclonal protein >30 g/L, IgA monoclonal protein, or Bence Jones proteins >50 mg/day to assess for impending bone complications. 2
Risk stratification: The presence of abnormal spinal MRI findings in smoldering myeloma patients predicts progression to symptomatic disease, with median time to progression of less than 1 year in those with abnormal MRI versus more than 3 years in those with normal findings. 2
Complications Specific to Lumbar Spine Involvement
Spinal cord compression occurs in approximately 20% of multiple myeloma cases and requires rapid diagnosis and treatment to prevent permanent neurological deficits. 3
Vertebral compression fractures: These are among the most common skeletal-related events, occurring due to the combination of osteolytic destruction and mechanical stress on weight-bearing vertebrae. 2
Pathologic fractures: Axial skeletal fractures of vertebral bodies may lead to spinal cord compression or vertebral body collapse with significant neurologic complications. 1