Quantifying rigidity with a new computerized elbow device.

A new computerized method is described for measuring parkinsonian rigidity with an elbow device. We present data from 127 subjects (103 controls and 24 parkinsonian patients) to show the clinical utility of the method. The instrumental quantification of rigidity correlates highly with clinical ratings of parkinsonian rigidity. The test-retest repeatability was excellent. In parkinsonian patients versus normal controls, significantly higher values of measured rigidity were observed. Moreover, activation procedure significantly increases rigidity only in parkinsonian patients. Activated rigidity in control subjects is lower than basal values. The procedure was sensitive to increased rigidity in parkinsonian patients during 3 days' drug holiday. Contrary to previous reports, levodopa therapy reduced both basal and activated rigidity in parkinsonian patients. This method is relatively simple and takes only 15 min to complete.