Literature Review
INDIANAPOLIS—Smoked cannabis may compromise cognitive function in patients with multiple sclerosis (MS), according to an overview presented at the 2015 Consortium of MS Centers Annual Meeting. Evidence does not support the hypothesis that cannabis affects mood or causes anxiety or psychosis, however. Clinicians should weigh the potentially harmful effects of cannabis on cognition against the drug’s possible benefits for pain, spasticity, and urinary problems.
Between 40% and 70% of people with MS have cognitive dysfunction, which may include deficits in information processing speed, working memory, visuospatial memory, or executive function, said Anthony Feinstein, MD, PhD, Professor of Psychiatry at the University of Toronto. Approximately 40% of patients with MS have used cannabis, and Dr. Feinstein studies the drug’s effects on cognition among patients with MS.
In 2008, he and his colleagues interviewed 140 consecutive patients with MS with the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) Axis I disorders. The researchers assessed cognition using the Neuropsychological Battery for MS, supplemented with the Symbol Digit Modalities Test (SDMT). When the investigators compared 10 current cannabis users with 40 matched controls with MS, they found that cannabis users had a slower mean performance time on the SDMT and a different pattern of response, compared with the matched controls.
In 2011, Dr. Feinstein and colleagues compared 25 patients with MS who smoked cannabis with 25 patients with MS who did not smoke cannabis. Participants underwent the Minimal Assessment of Cognitive Function in MS battery of neuropsychologic tests, the Hospital Anxiety and Depression Scale (HADS), and the Structured Clinical Interview for the DSM-IV Axis I Disorders. The two patient groups were matched for demographic and disease variables. Cannabis users were more likely to be unemployed than nonusers and also had more cognitive deficits, including in visuospatial perception, executive function, and information processing speed, compared with nonusers. The researchers found no differences between groups in depression or anxiety, however.
Finally, in 2014, Dr. Feinstein and colleagues performed a cross-sectional study of 20 patients with MS who smoked cannabis and 19 patients with MS who did not. Participants underwent fMRI while completing the N-Back test of working memory. Spatial memory and Paced Auditory Serial Addition Test scores were lower among patients who smoked cannabis. These patients also had slowed responses and more errors on the N-Back test, compared with cannabis nonusers. During this test, cannabis users also had increased activation in parietal and anterior cingulate regions implicated in working memory, compared with nonusers.
—Erik Greb