Structural Brain Imaging in People with Low Back Pain

Abstract

Low back pain (LBP) is a common chronic pain condition affecting millions of people worldwide. Conventional methods of diagnosing LBP have provided limited guidance; consequently most patients get a general diagnosis of “nonspecific” LBP. Brain imaging has been proposed to be a method of studying LBP since all pain signals are processed in the brain. Up till today, the relationship between brain structure and LBP is not fully understood. A few studies have examined this relationship but reported inconsistent findings. Additionally, all of those studies examined the chronic LBP population and none have attempted to study acute/subacute LBP population. In this study we have acquired structural brain scans from participants with LBP (acute/subacute and chronic) and healthy controls. A total of 130 participants were included in this study (23 subacute LBP participants, 68 chronic LBP participants, and 39 healthy controls). We compared whole-brain volume between each 2 groups separately using volumetric measurements and using voxel-based morphometry (VBM). We also examined specific regions-of-interest (ROIs) of pain processing. Finally we conducted correlation analyses between brain volumes and clinical outcome measures we collected from the LBP participants in the 2 groups. Our results showed no difference in whole-brain volume between any of the groups measured by volumetric measurements or VBM after correcting for multiple comparisons. We noticed difference in 2 voxels (6.75 mm3) in the cortical affective regions of the brain when comparing participants with chronic LBP to healthy controls. Normal aging can lead to an annual loss of 4-6 mm3 of brain volume; therefore the reduction we have noticed is not clinically significant. No differences were noticed in the other ROIs. Finally, no correlations were noticed between any of the clinical outcome measures and brain volumes. We calculated the effect size of LBP and found it to be <0.1, which is considered a minimal effect size. Our conclusion is that LBP has minimum to no-effect on brain structure regardless of its duration. This information is clinically important for patients, clinicians, and scientists for understanding the underlying neurophysiological consequences of LBP and therapeutic applications.