The relationship between motor symptom lateralization and cognitive performance in newly diagnosed drug-naive patients with Parkinson's disease

The side of motor symptom predominance may influence cognitive performance in patients with Parkinson's disease (PD): PD patients with right-side motor symptom predominance typically present difficulties in tasks of language and verbal memory, whereas PD patients with left-side motor symptom predominance typically present difficulties in visuospatial tasks. The current study aimed at investigating the relationship between motor symptom lateralization and cognitive performance in PD patients without the possible confounding effect of dopaminergic drugs, which may enhance or impair cognition on the basis of assessed function and disease stage. From the initial sample of 137 consecutive newly diagnosed drug-naive (de novo) PD patients, clinical follow-ups and neurological examinations identified 108 right-handed patients with a unilateral motor presentation or a clear motor asymmetry (59 right-PD: 54.6%; 49 left-PD: 45.4%). Any cognitive difference emerged between right-PD patients and left-PD patients at this disease stage. Scores of lateralized motor impairment severity correlated with some cognitive performances: Right motor impairment correlated with a measure of set shifting (Trail Making Test BA), and left motor impairment correlated with phonemic fluency and tasks with visuospatial material (Colored Progressive Matrices of Raven, ReyOsterrieth Complex Figure Copy and Immediate Recall). Findings of the current study supported the conclusion that the side of clinical motor predominance scarcely influences cognition in the early untreated stages of PD, suggesting that cognitive differences between subgroups of lateralized PD patients probably may appear in more advanced disease stages.