Can spasticity and dystonia be independently measured in cerebral palsy?

Selecting and evaluating appropriate treatments for children with cerebral palsy has been challenging. One difficulty is in the ability to quantify the presence and importance of coexisting motor signs. This study presents quantitative measures developed to assess spasticity and dystonia. Children diagnosed with extrapyramidal or spastic cerebral palsy and matched control children were studied. Spasticity was measured as the slope of the force-velocity relationship from a test where we measured the forces required to passively extend the elbow at different velocities. Dystonia was assessed by measuring "overflow" movements of arm during active movement of the other arm. Measures of dystonia and spasticity did not correlate with one another, but did correlate with their respective clinical measurement tools, the Modified Ashworth scale and the Barry-Albright Dystonia scale. Most children had a combination of both spasticity and dystonia, despite diagnosis. Our measures also related to different aspects of reaching: children with increased dystonia made more curved paths, and children with increased spasticity hit higher peak velocities. These measurements allow us to distinguish between different motor disorders and the degree to which each contributes to reaching performance. Use of quantitative measures should improve selection and evaluation of treatments for childhood motor disorders.