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. Although neck hypertonus has been well described in progressive supranuclear palsy, little is known about the involvement of the truncal muscles. METHODS Muscle tonus of the neck and trunk was separately investigated in 13 patients with progressive supranuclear palsy by clinical examination and surface EMG during passive rotation. Muscle hypertonus was graded according to a four point scale, and subjected to statistical analysis. The results were compared with those from 13 age matched patients with Parkinson's disease and six healthy volunteers. RESULTS In all but one patient with progressive supranuclear palsy, there was a distinct 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 moderately increased tonus was noted in the truncal muscles (neck v trunk, shortening 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 disease, however, no significant difference was found in muscle rigidity between the neck and trunk. CONCLUSION Mild changes in truncal muscle tonus with prominent neck dystonia and rigidity are characteristic of progressive supranuclear palsy. It is suggested that separate clinical evaluation of muscle tonus in the neck and trunk may be helpful for distinguishing progressive supranuclear palsy from Parkinson's disease.