Dual task performance in Parkinson's disease: A sensitive predictor of impairment and disability

Background: Dual task (DT) performance assesses the ability to perform two tasks simultaneously. Difficulty with DT performance may be a sensitive indicator of early Parkinson's disease (PD) impairment. The objective of this study was to assess what elements of a DT performance (cognition or gait) are most associated with impairment and disability in PD. Methods: Performance in single and DT conditions was examined in 154 PD patients. The single task assessments included the time required to walk 50 feet (gait speed) and the number of words generated in a verbal fluency task (word generation). The DT comprised simultaneous performance of the single tasks. Impairment and disability were measured with the Unified Parkinson's Disease Rating Scale, Hoehn &Yahr, Berg Balance Scale, and Older Americans Resource and Services Scale. Age, education, and gender were control variables. Standardized residuals from regressions of DT upon single task performance were computed separately for word and gait, indicating the extent that the individual performed proportionally better/worse than predicted in DT considering their single task performance. Results: Multiple regressions revealed that individuals who performed worse than expected in DT-word had greater impairment and disability. Dual task-gait was not significant in any model. Verbal fluency during DT performance is more closely associated with PD-related impairment and disability than gait speed during DT. Conclusion: This suggests that subjects prioritize gait performance at the expense of cognitive performance, and that DT word generation may be a sensitive indicator of early PD impairment and disability. (C) 2012 Elsevier Ltd. All rights reserved.