Cannabis for neuropathic pain in multiple sclerosis-high expectations, poor data

Abstract

Pain affects around two-thirds of people with multiple sclerosis (PwMS) (Amatya et al., 2018). MS-related pain includes headache (43%), neuropathic pain in the arms or legs (26%), back pain (20%), painful spasms (15%), and trigeminal neuralgia (3.8%) (Foley et al., 2013). The prevalence of neuropathic pain in PwMS, which arises from peripheral or central nerve injury (described by sufferers as the “most terrible of all tortures which a nerve wound may inflict”), dramatically reduces the quality of life of PwMS (Kenner et al., 2007; Jaggi and Singh, 2011). The point prevalence of neuropathic pain in PwMS is nearly 50%, and approximately 75% of patients report having had pain within one month of assessment (O'Connor et al., 2008). Pharmacological treatment in MS-related neuropathic pain principally consists of the use of tricyclic antidepressants, antiepileptic medications, baclofen, anesthetics, and antiarrhythmic agents. However, these treatments are usually unsatisfactory and often have severe side effects (Solaro et al., 2007). Importantly, inadequate neuropathic pain therapy is one of the contributors to the opioid crisis in the US, and therefore, a need for alternative methods of neuropathic pain relief in PwMS is critical (Rummans et al., 2018). Many anecdotal reports suggest that cannabis and its major cannabinoid components have beneficial effects on pain, particularly neuropathic pain, in PwMS. However, little scientific evidence supports these anecdotes. Many reviews (Zhornitsky and Potvin, 2012; Jawahar et al., 2013; Koppel et al., 2014; Whiting et al., 2015) agree that cannabis might have a positive effect on pain in MS. Unfortunately, most (overview in Nielsen et al., 2018) did not address issues of trial quality and included different drugs, doses, durations, conditions, and outcomes. Thus, several issues regarding cannabis use to treat neuropathic pain in PwMS remain unresolved.