TRUNCAL MUSCLE TONUS IN PROGRESSIVE SUPRANUCLEAR PALSY

Objective-To elucidate the character and distribution of the abnormal muscle tonus in the body axis in progressive supranuclear palsy, Altho ugh neck hypertonus has been well described in progressive supranuclea r palsy, little is known about the involvement of the truncal muscles. Methods-Muscle tonus of the neck and trunk was separately investigate d in 13 patients with progressive supranuclear palsy by clinical exami nation and surface EMG during passive rotation. Muscle hypertonus was graded according to a four point scale, and subjected to statistical a nalysis. The results were compared with those from 13 age matched pati ents with Parkinson's disease and six healthy volunteers. Results-In a ll but one patient with progressive supranuclear palsy, there was a di stinct difference in muscle tonus between the neck and trunk, A tonic shortening reaction characteristic of dystonia and an increased tonic stretch reflex (rigidity) were present in the neck muscles of patients with progressive supranuclear palsy, whereas only normal to moderatel y increased tonus was noted in the truncal muscles (neck er trunk, sho rtening reaction p=0.0001; stretch reflex p=0.0241). Follow up studies disclosed an increase in axial muscle tonus with predilection for the neck in three of four patients. In the 13 patients with Parkinson's d isease, however, no significant difference was found in muscle rigidit y between the neck and trunk. Conclusion-Mild changes in truncal muscl e tonus with prominent neck dystonia and rigidity are characteristic o f progressive supranuclear palsy. It is suggested that separate clinic al evaluation of muscle tonus in the neck and trunk may be helpful for distinguishing progressive supranuclear palsy from Parkinson's diseas e.