The role of motor subtypes in modulating neuropsychiatric and cognitive function in Parkinson's disease: A group-stratified mediation analysis.

This study investigates the disparities in neuropsychiatric symptoms and cognitive function, focusing on how motor subtypes modulate the interplay among depression, apathy, and cognition among Parkinson's disease (PD). We enrolled 176 participants (106 Normal Controls [NCs], 21 Tremor Dominant [TD], and 43 Postural Instability and Gait Difficulty [PIGD]), assessing motor symptoms, neuropsychiatric symptoms, and neuropsychological function. Comparisons between groups assessed depression, apathy, and cognitive decline. Mediation analyses explored motor subtypes' role in apathy mediation. We found the PIGD exhibited significantly higher depression levels than the TD group. The TD maintained better global cognition and executive function, comparable to NCs, and superior to PIGD. Post-hoc analyses showed NCs excelled in attention and memory over PIGD, with TD showing intermediate but comparable performance, indicating a less pronounced cognitive decline. Mediation analysis showed no significant mediating effect of apathy, but highlighted depression's significant impact on cognitive performance in PIGD, affecting executive function (i.e., mental shifting, category fluency) and delayed visual memory. In conclusion, the TD subtype maintained better overall cognition and executive function with minor attention and memory issues, while PIGD showed a stronger correlation between depression and cognitive decline, suggesting targeted early intervention for depressive symptoms in PIGD could enhance cognitive outcomes.