Abnormalities of Nerve Conduction Study in Myotonic Dystrophy: Primary Involvement of Nerve? or Incidental Coexistence?

J Korean Assoc EMG Electrodiagn Med 2006;8(1):33-39.
Published online May 10, 2006.

Abstract

Objectives: Involvement of peripheral nerves in myotonic dystrophy (DM) is still controversial and the features of neuropathies are not well known. The aims of the study are to assess the frequencies of abnormal nerve conduction findings and electrophysiological characteristics of peripheral neuropathy in DM. Methods: We analyzed medical recordings, nerve conduction studies (NCS), and results of genetic analysis of 18 patients with DM and 30 healthy subjects. The early changes in NCS were determined using a sural/ulnar sensory nerve action potential amplitude ratio (SUAR). To correlate the neuropathic changes with cardiac abnormality, we compared corrected QT interval (QTc) with the NCS parameters. Results: Eight patients out of 18 showed abnormal NCS. Of these, abnormal peroneal motor NCS and H-reflex abnormalities were most common. Only one patient complained sensory symptoms and showed abnormal sensory and motor NCS compatible with sensorimotor axonal polyneuropathy. There was no significant correlation between SUAR and disease duration, age, CTG repeats or corrected QT interval of electrocardiogram. Presence of diabetes mellitus was not related with the presence of abnormal NCS or SUAR. Conclusion: Comparing with previous reports, frequency of peripheral neuropathy or abnormal NCS in DM was low in our study. Our conclusion from this study is that abnormal NCS in DM seems to be resulted rather from myopathic changes or coincidental neuropathies or radiculopathies than primary involvement of nerve by DM.

Key Words: Myotonic Dystrophy, Neuropathy, Neural Conduction, Abnormalities