Phenotype matters: the absence of a positive association between cortical thinning and chronic low back pain when controlling for salient clinical variables

AIMS/OBJECTIVES/BACKGROUND: Studies have associated chronic low back pain (cLBP) with grey matter thinning. But these studies have not controlled for important clinical variables (such as a comorbid affective disorder, pain medication, age, or pain phenotype), which may reduce or eliminate these associations.
METHODS: We conducted cortical thickness and voxel-based morphometry (VBM) analyses in 14 cLBP patients with a discogenic component to their pain, not taking opioids or benzodiazepines, and not depressed or anxious. They were age and gender matched to 14 pain-free controls (PFCs). An ROI-driven analysis (regions of interest) was conducted, using 18 clusters from a previous arterial spin labeling study demonstrating greater regional cerebral blood flow (rCBF) in these cLBP subjects than the PFCs. Cortical thickness and VBM-based gray matter volume measurements were obtained from a structural MRI scan and group contrasts were calculated.
RESULTS: Multivariate analysis of variance showed a trend toward cortical thickening in the right paracentral lobule in cLBP subjects (F1,17=3.667, P CONCLUSIONS: Our pilot results suggest that controlling for affect, age, and concurrent medications may reduce or eliminate some of the previously reported structural brain alterations in cLBP.