Comment on: “A Transatlantic Viewpoint on the Role of Pallidal Stimulation for Parkinson's Disease”

Abstract

We recently published an invited editorial on the article by Domen et al reporting on cognitive safety of cannabis products in Parkinson's disease (PD). Briefly, they conducted a randomized, controlled trial to determine whether cannabidiol (CBD)/ Δ9-tetrahydocannabinol (THC) products improved PD motor symptoms and assessed for potential impact on cognition using a battery of neuropsychological tests. Treatment was associated with less benefit from practice on a verbal fluency test and increased reporting of adverse cognitive events. Results from the primary motor outcome are pending. Our editorial highlighted the methodological strengths and importance of their work. As PD clinicians, we wondered whether two important questions could be addressed by this study: (1) is risk of adverse impact of CBD/THC on cognition dependent on cognitive status (ie, "normal" vs. mild impairment or dementia)? (2) What is the overall impact of CBD/THC on cognition in PD? We were most pleased that the authors responded to our editorial and addressed our questions. Unfortunately, although their study sample included PD patients with cognitive impairment, there were not enough impaired individuals to examine whether this had bearing on side effects. However, in a well-executed follow-up analysis, they found that placebo appreciated greater overall improvement via practice effect than treatment, with a medium to large effect size. This finding aligns with subjective reporting of adverse cognitive events. Thanks to the efforts of Domen and colleagues, we now have solid empirical evidence to inform PD patients about potential cognitive risks associated with CBD/THC. We look forward to reading results on the motor functioning to see whether there are benefits to justify the risks.