Assessment of autonomic function in myotonic dystrophy.

Published reports suggested autonomic nervous system dysfunction in myotonic dystrophy but were inconclusive partly due to small patient numbers and because only a limited number of tests was used. Autonomic nervous system function with noninvasive tests was assessed in ten myotonic dystrophy patients and age and sex matched healthy controls. Statistically significant differences included reduction in the heart rate response to standing and in the blood pressure response to sustained handgrip. Latency of the pupillary light reflex was not different from controls but the time to reach peak velocity of contraction was significantly longer in the myotonic dystrophy group. It is argued that these results reflect dysfunction of voluntary and iris smooth muscle rather than autonomic nervous system dysfunction.