Lower Extremity Radicular Pain Relieved With Tetrahydrocannabinol
In a small (n = 17 men), double-blind, placebo-controlled study using a counterbalanced within-subjects design, treatment of patients with chronic neuropathic pain with delta-9-tetrahydrocannibinol (THC) resulted in a significant reduction in perceived pain (P < .005) compared to placebo (P < .05). (Neurology. 2018;91:1-10.) Women were excluded from the study to control for effect of hormone fluctuations during menstruation on pain.
In a first visit, all patients rated their pain using a 100-point visual analog scale (VAS) and had a functional MRI (fMRI); 9 subjects assigned randomly were then given 15 mg THC oil sublingually and 5 were given a placebo. Pain rating and fMRI were repeated 2 hours after treatment. The fMRI analysis focused on the anterior cingulate cortex (ACC) and pain-related network dynamics using graph theory measures. In a second visit, at least 1 week later, this was repeated, with patients who’d been given THC previously now given placebo and vice versa. Repeated measures of variance analyses were done for each subject to distinguish significant interaction and simple main effects between treatment versus placebo and pretreatment versus posttreatment VAS scores.
Treatment with THC significantly reduced patients’ pain compared to placebo and THC-induced pain relief correlated in a predictive degree with reduced functional activity between the ACC and the sensorimotor cortex. There was also significant reduction in network connectivity in areas involved in pain processing, specifically in the dorsolateral prefrontal cortex (DLPFC) that also were correlated with individual pain reduction.
These results suggest that the ACC and DLPFC, major cognitive-emotional areas, connections to somatosensory areas, are functionally involved in the analgesic effect of THC in chronic pain. It is hypothesized that the baseline functional connectivity between these brain areas may serve as a predictor for the extent of pain relief induced by THC.
“Pain is a complex experience that involves both the senses and emotions,” said study author Haggai Sharon, MD, of the Sagol Brain Institute, Tel Aviv Medical Center in Israel. “Our study results link pain relief from THC with a reduction in the connections between areas of the brain otherwise heavily connected, suggesting that THC may alleviate pain by disrupting signals between these pain processing pathways.”