Kelly Hughes

Tags: cannabis; multiple sclerosis; cannabis withdrawal; cognitive impairment

 

The problem: An estimated 20% of multiple sclerosis (MS) patients use cannabis for one reason or another and this number is expected to increase as cannabis legalization becomes more widespread. Cognitive dysfunction affects 40–80% of patients with MS and studies suggest that using cannabis may add to these cognitive deficits.

 

Why do this study? It’s not known whether the cognitive impairment related to cannabis use in MS patients can be reversed, and if stopping cannabis use results in cognitive improvement.

 

The study: This study enrolled 40 patients with MS who started using cannabis after the onset of the disease and who used it for at least 4 days a week. Patients were eligible for the study if they had evidence of cognitive impairment; defined by failing 2 or more areas evaluated by the Brief Repeatable Neuropsychological Battery (BRNB) for multiple sclerosis. BRNB assessments included tests of verbal and visual memory, processing speed and executive function, and structural and functional MRI. Eligible patients were randomly assigned to either continue or stop cannabis use. Patients were assessed for baseline cognitive function at the start of the study, and then again after 28 days; at which point a urine test was administered to detect cannabis use or abstinence

 

There were no baseline differences between the two groups at the start of the study, but by day 28 the withdrawal group performed significantly better on every cognitive test; including memory, processing speed and executive function. Functional MRI assessments showed no difference between groups at the start of the study, but did reveal some improvement in responses from the withdrawal group by day 28 (however this result was not statistically significant). Structural MRI assessment revealed no difference between the two groups throughout the study.

 

Conclusions: For patients with MS who are frequent, long term cannabis users, abstaining from cannabis use for 28 days can lead to significant, wide-ranging improvements in cognitive function. The comparative lack of improvement in patients who remained on cannabis shows that these improvements are not simply due to patients becoming more practiced at taking the cognitive assessments.

 

What does this study add?  This study found that cognitive impairment in MS patients can be reduced by stopping cannabis. Previous studies suggest that cannabis use may compound MS-related cognitive impairments, but do not address the issue of reversing it. This study also adds a timeline over which these effects can be remedied.

 

Funder: Multiple Sclerosis Society of Canada

 

Author conflicts: One author, A.F., has received awards and compensation from various pharmaceutical and publishing companies, as stated here: speaker’s honoraria from Sanofi-Genzyme, Roche, Biogen, Teva and Novartis, Advisory Board fees from Akili Interactive, and book royalties from Cambridge University Press, Johns Hopkins University Press and Amadeus Press.

 

Commentary: (David Casarett MD)

 

The headline of this study is relatively straightforward:  patients with MS and cognitive dysfunction can improve if they stop cannabis.  But that conclusion begs one large question:  Do these differences matter?  Advanced neuropsychological testing can pick up very subtle deficits that may be invisible to patients, and their family and friends.  So we don’t really know whether these deficits—or their reversal—is clinically important.  Another question is whether, even if these differences are important, MS patients might accept them in order to get relief of pain and muscle spasms.  There are numerous legal drugs in use that impair cognition (e.g. opioids, benzodiazepines), but which are used because their benefits outweigh their risks.  So although this study is interesting, it’s important mostly because it lays the foundation for future research to define whether these deficits are meaningful, and how they should be balanced against improved symptom control.