Myasthenia gravis: relation between jitter in single-fiber EMG and antibody to acetylcholine receptor

In 39 patients with myasthenia gravis, we measured jitter in the extensor digitorum communis muscle, using single-fiber electrode (SFEMG) and the serum titer of antiacetylcholine receptor antibody. Clinical severity was correlated more closely with jitter, especially the percentage of abnormal jitter pairs with blocking than with antibody titer. In patients who responded fairly well clinically after certain treatments, both the SFEMG abnormalities and antibody titer tended to improve in parallel with clinical improvement. After the plasma exchange, there was a time lag between the recovery from the defective neuromuscular transmission and the rapid decrease in antibody titer. The percentage of abnormal jitter pairs with blocking and the mean jitter value reflect defective neuromuscular transmission in generalized myasthenia gravis.