MRI abnormal patterns of lumbar paraspinal muscles in patients with amyotrophic lateral sclerosis and lumbosacral radiculopathy: a comparative study

Background Recent evidence highlights the potential predictive value of paraspinal muscle degeneration in amyotrophic lateral sclerosis (ALS). However, the magnetic resonance imaging (MRI) characteristics of degeneration in lumbar paraspinal muscles in ALS and lumbosacral radiculopathy (LR) remain unclear. Methods Comparison of fatty infiltration (FI) and relative cross-sectional area (rCSA) of the paraspinal muscles was conducted between 38 ALS patients and 32 LR patients. Results The mean rCSA of the multifidus (MF), erector spinae (ES), and psoas major (PM) muscles was lower on the symptomatic onset side compared to the contralateral side at the L3–L5 segments in patients with ALS. On the symptomatic onset side, the FI of the ES (L1-L4 segments), MF (L4 segment), and PM muscles (L1, L2, and L4 segments) was significantly higher in ALS patients who had pathological spontaneous activity (PSA) than in those without PSA. At the L3-L5 segments on the symptomatic onset side, the mean rCSA of the MF, ES, and PM muscles was significantly higher in LR patients compared to ALS patients ( p < 0.01). Similar differences in the rCSA of the MF, ES, and PM muscles were observed between lower limb-onset ALS patients and LR patients ( p < 0.05). In addition, mild associations were observed between declines in the ALS functional rating scale (ALSFRS)-lower score and decreases in the rCSA of MF and PM muscles, as well as increased FI of the MF and ES muscles. Conclusion The decrease in the rCSA of the paraspinal muscles on the symptomatic onset side suggests progressive involvement of muscle fibers in ALS patients. The presence of PSA in the paraspinal muscles appears to be more valuable and sensitive for evaluating fatty substitution than muscle atrophy in ALS. MRI parameters of the paraspinal muscles may be useful for monitoring disease progression in ALS and distinguishing ALS, especially lower limb-onset cases, from pauci-symptomatic LR.