Abstract
Background: The primary influence of motor symptoms on driving performance remains unclear due to the inconsistent use of various motor rating scales used in prior studies. Objective: This study aimed to determine which of three measures utilized in PD, the Unified Parkinson's Disease Rating Scale (UPDRS) motor section; the Modified Hoehn and Yahr; and the Rapid Paced Walk Test would best predict pass/fail outcomes on a road test in a sample of PD drivers. Methods: All participants (N = 55; 79% men) completed a road test. Receiver Operating Characteristics were then contrasted for all subjects based on assessments from all three disease severity indices. MMSE scores were then modelled with significant disease severity measures (if any) to determine if the predictive accuracy could be improved. Results: The Rapid Paced Walk Test and the Modified Hoehn & Yahr both predicted pass/fail outcomes on the road test (Area under the curve of 0.73 and 0.82, respectively). UPDRS motor scores, however, did not predict safe driving. When optimal cut-off points on the Modified Hoehn & Yahr (≥2.5) and Rapid Paced Walk Test (>6.22 seconds) were modelled with MMSE scores indicative of mild cognitive impairment (<27), the model accurately classified 92% and 100% as failing the road test, respectively. Conclusion: Although the Rapid Paced Walk Test had a slight advantage in differentiating between pass/fail outcomes compared to the Modified Hoehn & Yahr, both tests alone cannot be used in isolation to predict driving safety. Predictive accuracy can be improved using both select cut-off points on the Modified Hoehn & Yahr and Rapid Paced Walk test with MMSE scores in PD drivers. Though these findings are useful, an on-road test is still the gold standard, and screening should always be followed by formal testing.