Magnetic Resonance Spectroscopic Analysis of Multifidus Muscle Lipid Contents and Association with Nociceptive Pain in Chronic Low Back Pain

Abstract

Study design: Cross-sectional study.

Purpose: This study aimed to analyze the differences in the lipid contents in chronic low back pain (CLBP) patients with nociceptive pain (NocP) and neuropathic pain (NeP) using magnetic resonance spectroscopy (MRS) of the multifidus muscle (Mm).

Overview of literature: Early identification of the pain characteristics with CLBP is important because specific treatment approaches are required, depending on NocP and NeP.

Methods: The participants were 50 patients with CLBP (23 men and 27 women; mean age, 63.1±17.8 years; range, 41-79 years). We compared the Visual Analog Scale (VAS) scores, intramyocellular lipids (IMCLs) and extramyocellular lipids (EMCLs) of the Mm in NocP and NeP groups, as evaluated with the Japanese NeP screening questionnaire.

Results: The patients were categorized into the NocP (n=32) and NeP (n=18) groups. The mean VAS score of the NocP group was 59.3±3.1 mm and that of the NeP group was 73.6±4.6 mm. The mean VAS score was significantly higher in the NeP group as compared to that in the NocP group (p<0.01). As per the analysis of covariance for the VAS score, the mean IMCL levels of the Mm in the NocP and NeP groups were 722.3 mmol/L (95% confidence interval [CI], 611.4-833.1) and 484.8 mmol/L (95% CI, 381.1-588.5), respectively. The mean IMCL level was significantly higher in the NocP group than in the NeP group (p<0.05). The mean EMCL levels of the Mm for the NocP and NeP groups were 6,022.9 mmol/L (95% CI, 4,510.6-7,535.2) and 5,558.1 mmol/L (95% CI, 4,298.3-6,817.9), respectively; however, the difference was not significant (p=0.72).

Conclusions: The results indicated an association between the IMCL level of the Mm and NocP. Our results suggest that MRS of the Mm might be beneficial for the assessment of CLBP as well as appropriate targeted analgesic therapies.

Keywords: Low back pains; Magnetic resonance imaging; Nociceptive pains; Paraspinal muscle.

Fig. 1.

Volume of interest for magnetic resonance spectroscopy measurements of the right multifidus muscle as indicated on the T2 weighted-image at the L4/5 level.

Fig. 2.

Proton magnetic resonance spectrum of multifidus muscle analyzed using LCModel software (Stephen Provencher Inc., Oakville, ON, USA). The following metabolites are identified; IMCLs (–CH2) methylene protons at 1.3 ppm; EMCLs (–CH2) methylene protons at 1.5 ppm. IMCLs, intramyocellular lipids; EMCLs, extramyocellular lipids.

Fig. 3.

Bar chart of the number of patients in each neuropathic pain (NeP) score. Patients were categorized into the nociceptive pain (NocP) group (n=32) and the NeP (n=18) group.

Fig. 4.

Bar chart showing Visual Analog Scale (VAS) scores in the nociceptive pain (NocP) and neuropathic pain (NeP) groups. VAS scores were significantly higher in the NeP than in the NocP group (p<0.01). Error bars denote the standard error of the mean. ^*p<0.01 (by the Mann-Whitney U-test).

Fig. 5.

Bar chart showing intramyocellular lipids (IMCLs) (A) and extramyocellular lipids (EMCLs) (B) of the multifidus muscle in the nociceptive pain (NocP) and neuropathic pain (NeP) groups. The mean IMCLs was significantly higher in the NocP than in the NeP group. The mean EMCLs was not significantly different between the NocP and NeP groups. Error bars denote the 95% confidence interval. ^*p<0.05 (by the analysis of covariance as covariance of Visual Analog Scale score).