Psychomotor processing and functional decline in Parkinson's disease predicted by the Purdue Pegboard test

The Purdue Pegboard test (PPT) assesses upper-extremity dexterity and motor skills. We hypothesized that PPT skill would predict functional and cognitive decline in Parkinson's disease (PD), independent of observer-rated measures of motor impairment.

We utilized data from 399 PD participants enrolled in the deprenyl and tocopherol antioxidative therapy of Parkinsonism trial. Unified Parkinson Disease Rating Scale (UPDRS) metrics, neuropsychological assessments, and clinical rating scales were extracted for analysis with multivariate linear mixed-effects and generalized estimating equation regression models.

In multivariate logistic regression, higher baseline and time-varying PPT scores predicted better visual processing speed and attention throughout longitudinal follow-up. No similarly strong associations were found for tests of memory, nonvisual attention, phonemic fluency, or set-shifting. Independently of observer-rated motor impairment (UPDRS part III), PPT performance was significantly associated with changes in activities of daily living (ADL) function measured with UPDRS part II. Low baseline PPT score (≤10th percentile) doubled the relative risk of later ADL dysfunction (≥90th percentile).

PPT impairment selectively predicted declining psychomotor processing speed in PD. The domain-specificity of this association may reflect correlated pathophysiological changes in top-down visual and motor control pathways. PPT also predicted increasing ADL dysfunction after adjusting for objective measures of motor impairment. We suggest that PPT scores may be prognostically useful for predicting cognitive changes and ADL dysfunction, which have dramatic impacts on both patient and caregiver quality of life. Furthermore, simple task-based assessments like the PPT could be investigated for remote assessment in PD.