Determinants of fitness to drive in Huntington disease.

Objectives: To identify the most accurate clinical predictors of fitness to drive (FTDr) in Huntington disease (HD).

Methods: This cross-sectional study included 60 active drivers: 30 patients with manifest HD (8 women) and 30 age- and gender-matched healthy controls. Mean (SD) age of the HD group was 50 (12) years and median (Q1-Q3) disease duration was 24 (12-48) months. A clinical battery consisting of a driving history questionnaire, the cognitive section of the Unified Huntington's Disease Rating Scale (UHDRS), Trail Making Test, and Mini-Mental State Examination, as well as a driving simulator evaluation, were administered to all participants. Additionally, the subjects with HD completed the motor, behavioral, and Total Functional Capacity sections of the UHDRS and underwent an official FTDr evaluation comprising visual, neuropsychological, and on-road tests. The blinded neurologist's appraisal of FTDr and the 3 most predictive clinical tests were compared with the official pass/fail FTDr decision.

Results: The patients with HD performed worse on all tests of the clinical battery and driving simulator than the healthy controls. Fifteen patients with HD (50) failed the FTDr evaluation. The blinded neurologist correctly classified 21 patients (70%). The Symbol Digit Modalities Test, Stroop word reading, and Trail Making Test B provided the best model (R(2) = 0.49) to predict FTDr, correctly classifying 26 patients (87%).

Conclusions: Half of active drivers with HD fail a driving evaluation and pose a potential hazard on the road. Our results suggest that those at risk can be accurately identified using a clinical screening tool.