Further, because paraspinal and PS muscles have different nerve supplies (dorsal vs. ventral rami of lumbar nerves, respectively) selleckchem and MFI is increased bilaterally, denervation is not considered a plausible explanation in the current study. Finally, the positive correlation between fatty infiltration and episode frequency (mean: 4.4, min: 2, max: 9 per year; R2 = 0.450), may suggest a role for nociception in fatty infiltration.

This assumption is consistent with previous observations of generalized inhibition of MF, ES and PS recruitment with experimentally-induced pain ( Dickx et al., 2008; D’Hooge et al., submitted for publication). Further research is required to determine if peripheral nociception is involved in fatty infiltration via a reflex-mediated decrease in neural drive. Previously, Hultman

et al. (1993) found no difference in paraspinal muscle density on CT during remission of intermittent LBP. Results of fatty infiltration in the presence of LBP are less consistent than CSA measures. Some authors demonstrate increased fatty infiltration (Parkkola et al., 1993; Hultman et al., 1993; Mengiardi, 2006; Kjaer et al., 2007), whereas others show no difference to healthy controls (McLoughlin et al., 1994; Danneels et al., 2000; Kjaer et al., 2007). The discrepancy in results may be due to methodological JNK animal study differences such as the ROI in which fatty infiltration is determined (total vs. lean muscle, isolated MF vs. paraspinals grouped) or measuring technique (qualitative vs. quantitative, CT vs. MRI). The current study measured fatty infiltration

in two complementary modes yielding divergent results: lean fatty infiltration was increased, without macroscopic alterations. Similarly, Mengiardi (2006) revealed increased metabolic fat content with proton MR spectrocoscopy, which was not detectable with a semi-quantitative visual grading system using conventional MRI. Using a multifaceted approach to investigate lumbar muscle structure, the current study showed that fatty infiltration in lean muscle tissue was increased, without alterations in muscle size or macroscopic fat deposition during MRIP remission of LBP. This emphasizes the importance of differentiating muscle quantity (CSA) and quality (composition). In this respect, Elliott et al. reported enlarged cervical muscle CSAs and fatty infiltration in relation to whiplash-associated disorders, acknowledging that caution must be exercised during interpretation of CSA measurements in the presence of intramuscular fat (Elliott et al., 2008a, 2010). Similarly, lean fatty infiltration may be masking a reduction in muscle size in our results. It is assumed that fatty infiltration may negatively affect muscle contractility when muscle fibers are replaced with non-contractile tissue. Consequently, the deteriorated muscle composition may contribute to LBP recurrence.