Deterioration of motor function in myotonic dystrophy and hereditary motor and sensory neuropathy.

In order to obtain more information about the deterioration of motor function in patients with myotonic dystrophy and in patients with hereditary motor and sensory neuropathy, changes in strength and functionality were determined at one year intervals, over a follow-up period of 1 to 5 years. Twenty-five myotonic dystrophy patients and 16 hereditary motor and sensory neuropathy patients participated. Strength measurements were restricted to knee extension and flexion torques measured isokinetically on a dynamometer at two velocities (120 and 60 degrees/s). Functionality was measured as scaled time scores for rising from sitting, rising from supine, walking and stair climbing. Myotonic dystrophy patients showed a reduction of knee extension torques at 60 degrees/sec (mean decrease per year 5.7 Nm, or 9%) as well as a decrease in functionality. Hereditary motor and sensory neuropathy patients showed no statistically significant changes in torques or functionality. The correlation between isokinetically measured knee extension torques and functional scores was statistically significant in myotonic dystrophy but not in hereditary motor and sensory neuropathy. No correlation was found between changes in torques and changes in functional scores.