Neural Correlates of Chronic Low Back Pain Measured by Arterial Spin Labeling

Abstract

Background The varying nature of chronic pain (CP) is difficult to correlate to neural activity using typical functional magnetic resonance imaging methods. Arterial spin labeling is a perfusion-based imaging technique allowing the absolute quantification of regional cerebral blood flow, which is a surrogate measure of neuronal activity. Methods Subjects with chronic low back and radicular pain and matched healthy normals, undergoing identical procedures, participated in three sessions—a characterization and training session and two arterial spin labeling sessions. In the first imaging session CP (if any) was exacerbated using clinical maneuvers and in the second session noxious heat was applied to the affected leg dermatome, the intensity of which was matched to the pain intensity level of the CP exacerbations for each back pain subject. Results The clinically significant worsening of ongoing CP (≥30%, n=16) was associated with significant regional blood flow increases (6–10 mm/100gr of tissue/min, p<0.01) within brain regions known to activate with experimental pain (somatosensory, prefrontal, and insular cortices) and in other structures observed less frequently in experimental pain studies, such as the superior parietal lobule (part of the dorsal attention network). This effect is specific to changes in ongoing CP as it is observed during worsening CP, but it is not observed after thermal pain application, or in matched, pain-free healthy controls. Conclusions Our findings demonstrate the use of arterial spin labeling to investigate the neural processing of CP, and they are a step forward in the quest for objective biomarkers of the chronic pain experience.