Virginia Thornley, M.D., Neurologist, Epileptologist
June 17, 2018
Fibromyalgia used to be a condition denoting excessive pain and was previously questionable as there was no testing that could prove or disprove it. Now, the current thought is that it is attributed to hypersensitivity of the nervous system to pain impulses resulting in multiple points of pain in the body.
Endocannabinoid system in pain modulation
The endocannabinoid system is a major chemical neurotransmitter system that has only come to light as to physiology in the last 20 years. The CB1 receptor is found predominantly in the nervous system on which the endogenous endocannabinoid anandamide exerts its effects. The CB2 receptor is found mostly in the immune system on which 2-Arachidonoylglycerol acts. In the nervous system, cannabinoid receptors are seen in the periaqueductal gray area, ventromedial medulla and dorsal horn of the spinal cord which are areas where pain transmission takes place. This suggests that endocannabinoids play a major role in modulation of pain and can impact pain control through manipulation of this system.
Anandamide and and 2-Arachidonoylglycerol are synthesized on demand. It is released immediately after production. 2-AG is formed from a 2 step process. Anandamide has a low affinity to the TPRV1 receptor (2).
1,2-diacylglycerol (DAG) is a precursor or 2-AG which is formed by hydrolysis of membrane phosphoinositides. DAG is hydrolyzed by 2-AG hydrolase to form 2-AG. 2-AG may be stimulated by activation of G protein receptor such as glutamate receptors. It activates both CB1 and CB2 receptors. Cannabidiol which is found in the cannabis sativa plant is a natural mimetic of 2-AG. Endogenous 2-AG is found 170 times more than Anandamide in the brain. Exogenous 2-AG suppresses nociceptive stimulus (2). 2-AG activity is potentiated with natural 2-acylglycerols which enhances the effects which does not happen when used alone. This is an entourage effect found in the brain where the combination of substances give a combined resulting effect which does not occur if used alone (2).
Mechanisms in pain modulation
Cannabinoids were found to reduce nociceptive transmission at the level of the pain c-fiber responses in the spinal dorsal horn.
Randomized controlled trial in fibromyalgia
In one study of 40 patients in a randomized controlled clinical trial, nabilone which is a synthetic cannabinoid was given over a 4 week period. Measures that were evaluated included the visual analog scale for primary outcome and for secondary outcome measure, tender points, secondary outcome measure, Fibromyalgia Impact Questionnaire (FIQ) at weeks 2 and 4 were used. There was statistical difference in treated vs. control groups for pain (P value< 0.02), anxiety (P<0.02 and FIQ (P<0.02). There were more side effects for the treated cohort compared tot he placebo controlled group. This study demonstrates that cannabinoids may be an effective treatment for fibromyalgia (1).
In one paper that reviewed 18 randomized controlled clinical trials of cannabinoids in chronic pain syndromes including fibromyalgia, cannabinoids were found to be an effective type of treatment. Despite the short duration of the trials, pain relief was effective and mild to moderate adverse effects were noted. Larger clinical trials are needed (2).
- Skrabek, et al, “Nabilone for the treatment of pain in fibromyalgia,” J. Pain, 2008, Feb., (9)2:164:173
- Lynch, et al, “Cannabinoids for treatment of chronic non-cancer pain: a systemic review of randomized trials,” Br. J. Pharmacology, 2011, Nov., 72(5):735-744