Adverse effects of chronic pain on neurobiological structure and function are increasingly being recognized due to ongoing research using brain-imaging technology. A new study helps to confirm the neuroanatomical and functional abnormalities associated with chronic low back pain, but it also offers hope that these brain changes can be reversed with effective pain therapies.
In a prospective, controlled study researchers at McGill University in Montreal, Canada, conducted structural MRI scans on 14 patients with chronic low back pain (CLBP) both before and 6 months following either spine surgery or facet joint injections for their condition [Seminowicz et al. 2011]. Additionally, 10 healthy control subjects had MRIs initially and at 6 months followup. Brain cortex thickness was assessed via structural MRI scans and subjects also performed a cognitive task during functional MRI scanning. In the report, appearing in the Journal of Neuroscience, comparisons were made between patients and controls, initially and at followup.
After treatment, patients with CLBP exhibited increased cortical thickness in the left dorsolateral prefrontal cortex (DLPFC), which had been thinner before treatment compared with controls. The DLPFC plays an important role in pain perception and its increased thickening correlated with reductions of both pain and physical disability. Additionally, increased thickness in the primary motor cortex was associated specifically with reduced physical disability. In terms of cognitive performance, left DLPFC activity during an attention-demanding task was abnormal before treatment in patients with CLBP but normalized following treatment.
An important confirmation of these results was evidenced by outcomes in those patients in whom treatment for CLBP had been unsuccessful. Three of the 14 patients seen at followup reported worse back pain or disability 6 months after treatment, and their brain scans indicated that gray matter had not regenerated at all. The authors conclude that their data suggest that functional and structural brain abnormalities resulting from chronic back pain — specifically in the left DLPFC — are reversible, and that successful treatment of CLBP also may restore more normal brain functionality in humans.
COMMENTARY: Prior Pain-Topics UPDATES have described how persistent pain can functionally affect cognition — eg, concentration and memory [here] — as well as structural abnormalities of gray matter density in different brain regions [see here and here]. For example, besides chronic back pain, adverse neuroanatomical and functional effects have been found among patients with irritable bowel syndrome, fibromyalgia, vulvodynia, complex regional pain syndrome, and various neuropathies.
While in many cases chronic pain appears to provoke thinning in the prefrontal cortex, other cortical and limbic structures also have been involved. However, in some instances, the reverse effect — ie, cortical thickening — has been observed in certain patients depending on duration of chronic pain and/or emotional reactions to pain (eg, catastrophizing). So, while chronic pain appears to be, at least in part, a disease of the brain, the full extent of neuroanatomical changes involved have not yet been consistently elaborated.
This current, prospective investigation by Seminowicz et al. offers some hope that alterations of cortical thickness may be reversible and that gray matter density and volume can regenerate to a more normal state following successful pain therapy. Unfortunately, as with most brain-imaging studies, the number of subjects in each group was small, making generalizations to a broader population tenuous.
It also could have been informative if a group of subjects with CLBP not undergoing any additional treatment had been evaluated during the 6-month period to help rule out naturally occurring improvements in brain structure or functionality. Furthermore, treatments for CLBP in this study involved invasive procedures — surgery and injections — usually reserved for recalcitrant conditions. So, it would be helpful to know if more conservative therapies — eg, pharmacotherapy, physical therapy, etc. — if successful, might produce similarly favorable neurological outcomes.
REFERENCE: Seminowicz DA, Wideman TH, Naso L, et al., Effective Treatment of Chronic Low Back Pain in Humans Reverses Abnormal Brain Anatomy and Function. J Neurosci. 2011;31(20):7540-7550 [abstract here].