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Progressive supranuclear palsy is characterised clinically by the presence of supranuclear downgaze palsy, parkinsonism, postural instability with frequent falls, and dementia. In this disease, hyperextension of the neck associated with dystonia and rigidity occurs often. 1 However, the involvement of truncal muscle tonus remains unclear, presumably because the methodology for clinical evaluation of truncal tonus has not been established. In addition, neck and truncal muscles are usually treated as one unit of axial muscles. 1-7 Although factors contributing to neck muscle hypertonus have been described clinically as rigidity, 4 5 7 dystonic rigidity, 1 2 or rigidity and dystonia, 3 6 no objective study has been performed.
Recently, Nagumo and Hirayama 8 developed a bedside technique to evaluate truncal muscle tonus, and they showed truncal rigidity in Parkinson's disease. In the present study, we examined muscle tonus of the neck and trunk separately in patients with progressive supranuclear palsy by means of clinical assessment and surface EMG to determine the character and distribution of abnormal muscle tonus in the body axis.
Subjects and methods
SUBJECTS
Thirteen patients, seven men and six women, with well characterised progressive supranuclear palsy 1-7 served as the primary study group (mean age (SD), 65.2 (7.0) years). Eleven of these were outpatients from the Department of Neurology, Yokohama City University School of Medicine, Yokohama, and the two others were outpatients from the Department of Psychiatry, Nanasawa Rehabilitation Center, Atsugi. The duration of the progressive supranuclear palsy symptoms ranged from one to seven years (mean duration (SD), 3.6 (1.6) years). Motor symptoms were advanced, with five patients at stage 3, five at stage 4, and three at stage 5 (mean (SD), 3.8 (0.8)) as defined by the Hoehn and Yahr scale. 9 All the patients were rated at stage 3 or greater, because they showed prominent postural instability with frequent falls. At the time of testing, seven patients were taking carbidopa-levodopa in combination with amantadine or droxydopa, three patients were taking amitryptiline, and three were not taking any medication.
Thirteen patients with typical clinical features of Parkinson's disease, eight men and five women (mean age (SD), 66.0 (6.1) years), and six healthy subjects, three men and three women, with no apparent neurological abnormality (mean age (SD), 62.1 (7.3) years) served as a...