Foot-tapping rate as an objective outcome measure for Parkinson disease clinical trials

To explore foot-tapping rate as a reliable and a valid measure of motor function in Parkinson disease (PD).

We present data from a randomized, single-blind, outpatient study and a randomized, double-blind, placebo-controlled, crossover, inpatient study. Fifty PD subjects completed the outpatient study. A Unified Parkinson Disease Rating Scale motor score was determined for each subject. Subsequently, finger tapping, alternate (between 2 pedals) and repetitive (on 1 pedal) foot-tapping rates, and gait were measured. Thirteen PD subjects completed the inpatient study. Each subject received a daily infusion of high-dose apomorphine (APO), low-dose APO, and placebo in random order over 3 days. In this subanalysis, we compared variance and reliability of the finger- and the foot-tapping techniques during the placebo day and compared the validity of these outcome measures to detect improvement in parkinsonism during high-dose APO infusion.

Alternate foot tapping was reliable (interclass correlation on the placebo inpatient day, 84%). Only foot tapping detected improvement in parkinsonism with high-dose APO treatment (a measure of validity). In the outpatient study, there was a significant correlation between alternate and repetitive tapping with finger tapping (R2 = 0.28 and 0.23, respectively) and Unified Parkinson Disease Rating Scale motor score (R2 = 0.09 and 0.08), but only alternate tapping correlated with gait (R2 = 0.16).

Alternate foot tapping was equally reliable but more valid than finger tapping. Alternate foot tapping correlated better did existing PD outcome measures than did repetitive foot tapping. Foot tapping may be a useful outcome measure for determination of dopaminergic medication effect in PD clinical trials.