Quantification of Muscle Spasticity Using MRI and Resistance to Passive Movement

Abstract

2298 Evaluation of muscle spasticity is based on subjective assessment of limb resistance to passive movement. Such assessment lacks the reliability and sensitivity to detect small or moderate changes in patient status. It would be useful to have an objective quantitative indicator of muscle spasticity, especially for the evaluation of efficacy of experimental treatments. PURPOSE: To perform a preliminary evaluation of magnetic resonance imaging (MRI) and resistance to passive movement for the evaluation of spastic muscle. METHODS: Six hemipeligic stroke survivors with muscle spasticity in the elbow flexors and extensors participated (56.2 ± 1.9 yrs). T2 weighted MRI scans of the upper arm were obtained at rest and following performance of 3 sets of 10 concentric repetitions of arm flexion/extension at 30% of maximal voluntary isometric contraction. Resistance to passive movement was measured subjectively (Ashworth) by a clinician and objectively by an isokinetic dynamometer where the lower arm was moved about the elbow at speeds of 5, 60, 90, and 120 degrees/sec. RESULTS: The affected muscle groups were weaker than the unaffected muscle groups (flexors- affected: 20.1 ± 5.1 N-M, unaffected: 58.1 ± 3.9 N-M; extensors- affected: 22.0 ± 1.7 N-M, unaffected: 56.5 ± N-M; p<0.001). The unaffected cross-sectional area (CSA) of the triceps muscle group was significantly larger than the affected side (6.04 ± 0.72 cm2 vs 4.55 ± 0.43 cm2; p=0.01), whereas no differences in the biceps muscle group was observed (5.27 ± 0.78 cm2 vs 5.02 ± 0.57 cm2). There was a tendency (p=0.07) for resting T2 to be higher in affected vs. unaffected biceps (30 ± 3 vs. 27 ± 3 msec) but triceps values were similar. In both biceps and triceps the unaffected side showed a significant (∼30%) increase in T2 after exercise and no exercise-induced change in T2 for the affected muscles. For the elbow flexors, a greater passive resistance to movement was observed for the affected side as speed of movement increased. At 90 degrees/sec, the exerted passive torque ranged from 0.33-3.57 N-M, despite all subjects receiving an Ashworth score of 1. The elbow extensors also displayed an increased passive resistance to movement with increasing speed, with a larger range of exerted torque values and Ashworth scores measured on the affected side (Passive torque range: 2.7-19.9 Newton-Meters, Ashworth score range: 0-3). CONCLUSION Both MRI and quantitative resistance to passive movement may be useful in the evaluation of spastic muscle.