Recording Fewer Than 20 Potential Pairs With SFEMG May Suffice for the Diagnosis of Myasthenia Gravis.

PURPOSE: Our aim in the current study was to determine the minimum number of SFEMG potential pairs required to confirm neuromuscular junction impairment and relate this number to disease severity.

METHODS: Ninety-four patients with myasthenia gravis (MG) attending the neuromuscular clinic from February 2013 to November 2015 were included. The SFEMG sensitivity was determined for each number of recorded pairs up to 20. In addition, we compared clinical and electrophysiologic characteristics between patients with abnormality within the first 3, 4 to 7, and ≥8 recorded pairs to determine whether this number is associated with disease severity.

RESULTS: Ninety-eight percent of patients had abnormal SFEMG, within 17 pairs in ocular MG, and within 15 pairs in generalized MG. All patients with generalized MG had at least one abnormal pair in the first five recorded pairs. Patients with three abnormal pairs apparent earlier during the test had more frequent bulbar, respiratory, and limb muscle weakness, and had higher mean jitter values and decrement values.

CONCLUSIONS: In most cases, an abnormal SFEMG examination can be demonstrated in the first 15 recorded potential pairs in patients with generalized MG, and in the first 17 pairs in patients with ocular MG, thus shortening the test time and decreasing patient discomfort while preserving test sensitivity.