Functional magnetic resonance imaging reveals dysfunction of the paraspinal muscles in patients with chronic low back pain: a cross-sectional study.

Background: Patients with chronic low back pain (CLBP) undergo structural changes of the paraspinal muscles; however, it is unclear if functional changes also occur. This study aimed to examine the metabolic and perfusion function changes in the paraspinal muscles of patients with CLBP as indirectly reflected by blood oxygen level-dependent (BOLD) imaging and T2 mapping.

Methods: All participants were consecutively enrolled at our local hospital from December 2019 to November 2020. Patients were diagnosed with CLBP in the outpatient clinic, and asymptomatic participants were considered to be those with no CLBP or other diseases. This study was not registered on a clinical trial platform. Participants underwent BOLD imaging and T2 mapping scans at the L4-S1 disc level. The effective transverse relaxation rate (R2* values) and transverse relaxation time (T2 values) of the paraspinal muscles were measured on the central plane of the L4/5 and L5/S1 intervertebral discs. Finally, the independent samples -test was used to assess the differences in R2* and T2 values between the 2 groups, while Pearson correlation analysis was used to determine their correlation with age.

Results: A total of 60 patients with CLBP and 20 asymptomatic participants were enrolled. The paraspinal muscles of the CLBP group had higher total R2* values [46.7±2.9 44.0±2.9 s; 95% confidence interval (CI): 1.2-4.2; P=0.001] and lower total T2 values (45.4±4.2 47.1±3.7 ms; 95% CI: -3.8 to 0.4; P=0.109) than did the asymptomatic participants. For the different muscles, R2* values for the erector spinae (ES) (L4/5: 45.5±2.6 43.0±3.0 s, 95% CI: 1.1-4.0, P=0.001; L5/S1: 48.5±4.9 45.9±4.2 s; 95% CI: 0.2-5.1; P=0.035) and the R2* values of the multifidus (MF) muscles (L4/5: 46.4±2.9 43.7±3.5 s, 95% CI: 1.1-4.3, P=0.001; L5/S1: 46.3±3.5 42.5±2.8 s, 95% CI: 2.1-5.5, P<0.001) of the CLBP group at both spinal levels were higher than those of the asymptomatic participants. In the patients with CLBP, the R2* values at the L4/5 (45.9±2.1 s) were lower than those at the L5/S1 (47.4±3.6 s; 95% CI: -2.6 to -0.4; P=0.007). The R2* values were positively correlated with age in both groups (CLBP group: r=0.501, 95% CI: 0.271-0.694, P<0.001; asymptomatic group: r=0.499, 95% CI: -0.047 to 0.771; P=0.025).

Conclusions: The R2* values were higher in the paraspinal muscles of patients with CLPB and may suggest metabolic and perfusion dysfunction of the paraspinal muscles in these patients.