Determining neuromuscular jitter using a monopolar electrode

Neuromuscular jitter was determined in the extensor digitorum communis (EDC) of 41 healthy control subjects and 8 patients with myasthenia gravis (MG). Standard single-fiber electromyographic (SFEMG) techniques were used, except that a monopolar electrode (MPE) was substituted for a single-fiber electrode (SFE). In normals, mean jitter for 20 pairs was 22.4 +/- 2.8 microseconds and the mean jitter for an individual pair was 22 +/- 5.6 microseconds. In the age range tested (18 to 49 years), jitter did not change with increasing age. When MPE jitter studies were repeated in 16 normals, mean jitter usually varied by less than 10% (mean 7.4% +/- 6.2%) and remained normal. Jitter was significantly increased in MG compared to normals 73 +/- 56 microseconds versus 22 +/- 5.6 microseconds (F = 149.4, P less than 0.0001). Using an analog pain scale, the discomfort during electromyography using MPE and SFE was compared between the left and right arms in 35 normals. MPEs caused less discomfort than SFEs (P = 0.0031), and were preferred (71% versus 20%) to SFEs (chi 2 = 9.21, P = 0.01). Based on these results, we conclude that MPE determined jitter studies are reproducible, can distinguish between normals and MG, and are associated with less discomfort than SFE.