Cognitive function is associated with the progression of non-tremor motor symptoms in Parkinson’s disease

Background: Parkinson’s disease (PD) is characterized by motor impairment which consists of tremor and non-tremor symptoms. Cognitive function may overlap with specific aspects of voluntary movement and action initiation. This study aims to investigate associations between global cognition and the severity and longitudinal progression of tremor and non-tremor motor symptoms in PD. Methods: As part of the Oxford Quantification in Parkinsonism (OxQUIP) study, 84 participants with PD were tested over seven visits at three-month intervals. At each visit, participants completed standardized global cognitive (MoCA) and motor (MDS-UPDRS-III) assessments. Tremor and non-tremor motor subscores were derived from corresponding MDS-UPDRS-III items. Linear mixed-effects models were calculated to analyze the effect of global cognition at baseline on the progression of (i) overall motor impairment, (ii) non-tremor motor symptoms, and (iii) tremor symptoms. Results: We did not find an association between MoCA scores and MDS-UPDRS-III severity, but there was a significant interaction between global cognition and the progression of motor impairment (p=0.005). Lower MoCA scores were linked with steeper progression of non-tremor motor symptoms (p<0.001), but not tremor symptoms (p=0.380). Conclusions: Global cognition at baseline is associated with the progression, but not severity, of motor impairment in PD; this finding is specific to non-tremor and not tremor motor symptoms. While both motor subdomains are known to be linked with dysfunction of sub-cortical circuits, non-tremor symptoms may also be influenced by disrupted cognitive inputs. Our results highlight the potential value of incorporating cognitive tools to complement motor examination in PD assessment.