Impulse Control Disorders Are Independent of Parkinson Disease Motor Subtypes

Objective: Impulse control disorders (ICDs) are clinically important nonmotor features of Parkinson's disease (PD). Tremor-dominant PD (TD-PD) has been associated with greater cerebello-thalamo-cortical involvement, whereas postural instability/gait difficulty-dominant PD (PIGD-PD) has been linked to more prominent basal ganglia and frontostriatal dysfunction. We therefore examined whether ICD symptoms differ by motor phenotypes. Methods: This cross-sectional study analyzed baseline data from the Parkinson's Precision Medicine Initiative (PPMI). Motor subtype classification was based on Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) criteria. ICD symptoms were assessed using the Questionnaire for Impulsive-Compulsive Disorders in Parkinson's Disease-Current Short Form (QUIP-CS) and evaluated across multiple levels of analysis using the standard screening definition and normalized QUIP-CS scores analyzed categorically and continuously. Temporal-alignment, subgroup, multivariable, and Bayesian analyses were performed to assess the robustness of the primary findings. Results: We analyzed 305 participants (173 TD-PD, 132 PIGD-PD). Screening-defined ICD positivity was similar between subtypes (21.4% vs 21.2%, OR = 1.01, 95% CI 0.58-1.76, p = 0.970). Continuous and categorical normalized QUIP-CS scores likewise did not differ between groups (continuous score: 0.0338 vs 0.0384, p = 0.674; categorical score: 3.5% vs 4.5%, p = 0.632). Temporally aligned, subgroup, and multivariable sensitivity analyses consistently supported the primary finding, and Bayesian analysis provided moderate evidence supporting the null hypothesis (BF01 = 7.21). Conclusions: ICD symptoms do not differ between TD-PD and PIGD-PD motor subtypes in early PD. These findings suggest that motor subtype-associated differences in cerebellar involvement do not substantially influence ICD symptoms in early PD.