Unilateral versus bilateral tasks in early asymmetric Parkinson's disease: differential effects on bradykinesia.

Patients with Parkinson's disease (PD) have an impaired ability to perform two different simultaneous bimanual tasks. The differential effects of unilateral versus bilateral identical tasks on the bradykinesia scores of the more and less affected limbs in PD have not been examined. Twenty-seven patients with early and asymmetric PD underwent blinded, videotaped assessment, independently for each limb, using the bradykinesia items of the Unified Parkinson's Disease Rating Part III, Motor subscale (mUPDRS) and a Modified Bradykinesia Rating Scale (MBRS), which assessed amplitude, speed, and rhythm of movements. We found that the score for finger tapping in mUPDRS and MBRS, the score of amplitude of finger tapping in MBRS, and the lateralized scores of mUPDRS (sum of Items 23 to 25) of the most affected side significantly improved during the bimanual task. The improvement was associated with longer duration of illness, higher total scores in mUPDRS, and higher lateralized bradykinesia scores of the most affected side. There was a simultaneous deterioration of the lateralized bradykinesia scores in MBRS (sum of Items 23 to 25) and Item 25 of mUPDRS (rapid alternating movements) of the least affected side in bimanual tasks. In conclusion, identical bimanual tasks facilitate movement of the most affected side in early asymmetric PD at the cost of motor degradation in the least affected side. This observation also highlights the need to perform tasks of bradykinesia in one limb at a time for best accuracy.