The P3a wave: A reliable neurophysiological measure of Parkinson's disease duration and severity.

Objective: The P3a is an event-related potential (ERP) associated with involuntary attention and dopaminergic function. As P3a is reduced at initial stages of Parkinson's disease (PD), our objective was to assess P3a as a possible marker of PD duration and severity.

Methods: Fifty-five patients were analyzed, 28 of which were at Hoehn and Yahr severity stage 1; 14 at stage 2; and 13 at stage 3. Seventeen patients were free of antiparkinsonian medication. PD duration was defined as the number of years between the onset of motor symptoms and the date of this study. Twenty-four healthy subjects were included as controls. An involuntary attention paradigm was administered while a digital EEG was obtained.

Results: The P3a amplitude was significantly lower in all PD groups compared to the control group (F(3,75)=5.10, p=0.003), especially for stages 2 (p=0.017) and 3 (p=0.008). A regression analysis showed that the disease duration predicted inversely the P3a (Fz channel amplitude: Coefficient=-0.148, p=0.006; Frontocentral amplitude: Coefficient=-0.125, p=0.003) after controlling for demographic and clinical variables, medication, general cognitive state, and depression.

Conclusions: This is the first study reporting P3a sensibility to PD duration and severity.

Significance: This ERP could represent a reliable biomarker of the disease progression.