On-road driving impairments in Huntington disease

Abstract

To determine the driving skill impairments and underlying visual, motor, and cognitive deficits that lead to failure on road testing in manifest Huntington disease (HD). Certified driving assessment experts scored performance on 13 specific on-road driving skills in 30 persons with HD and 30 controls and issued a pass/fail decision based on their overall impression. These on-road skill items were mapped onto an existing theoretical framework that categorized driving skills into operational, tactical, visuo-integrative, and mixed clusters. The HD group additionally completed a detailed off-road battery of motor, visual, and neuropsychological tests. The HD group performed worse on all on-road items. Fourteen drivers with HD (47%) failed the road test compared with none of the controls. Scores on the Total Functional Capacity scale discriminated significantly between pass and fail groups. Total on-road score and performance in operational, tactical, and visuo-integrative clusters correlated strongly (Spearman ρ >0.50) with the pass/fail decision. The off-road tests showed variable strengths of association depending on the level of driving skill. Selective attention was strongly associated (Spearman ρ >0.50) with the total on-road score and all driving clusters. HD affects driving at many levels due to motor and cognitive deficits and leads to unsafe road performance even in mild stages. The high failure rate on the road test and difficulties in all aspects of on-road driving suggest that monitoring of fitness to drive should be initiated in the early course of HD.