Quantitative analysis of electromyogram interference pattern in extraocular muscle

Turns and amplitude analysis of the electromyogram (EMG) interference pattern has been applied to the extraocular muscles for the first time in the literature, to the best of our knowledge. EMGs of 261 horizontal rectus muscles recorded during the past 18 years were retrospectively examined and divided into four categories according to the clinical diagnosis: 56 complete palsy due to neuropathy, 67 incomplete palsy due to neuropathy, 19 myopathy, and 119 normal. The number of turns per second and mean amplitude between a pair of successive turns were automatically calculated by computer. Significant differences (P < 0.05) were encountered in all data among the four clinical categories except for the number of turns between myopathy and normal. The number of turns was plotted against the amplitude in each muscle on an X-Y diagram. The data of completely paretic muscle showed less number of turns and smaller amplitude and were clearly distinguishable from the data of the other three categories on the X-Y diagram. The interference pattern of incomplete palsy and myopathy had smaller amplitude than that of normal muscle. However, most of the data overlapped on the X-Y diagram particularly between data of incomplete neuropathy and myopathy.