Background: Single fiber electromyography (SFEMG) is a sensitive technique for detecting abnormalities in neuromuscular transmission and is mainly used in the diagnosis of neuromuscular junction disorders, such as myasthenia gravis. While the process of denervation-reinnervation in amyotrophic lateral sclerosis (ALS) can also result in immature collateral nerve terminals and instability of neuromuscular transmission, the purpose of this study was to investigate the changes and clinical values of SFEMG in patients with ALS.
Methods: Volitional SFEMG was performed on the extensor digitorum communis (EDC) of 78 patients with ALS (men 52, women 26) who had been previously diagnosed by history, clinical features, and neurophysiological studies. The mean jitter, the percentage of jitter >55 micros, the impulse blocking percentage, and fiber density (FD) were determined. These results were compared to normal controls. In addition, the SFEMG indices were analyzed for correlations with the duration of ALS, the EDC strength score on the Medical Research Council (MRC) scale, and spontaneous activity detected by EMG studies.
Results: SFEMG indices were abnormal in all patients with ALS. Mean jitter ranged from 30 to 178 micros (mean 80.2 micros); the percentage of jitter >55 micros ranged from 5% to 100% (mean 60.5%). In addition, the impulse blocking percentage ranged from 0% to 90% (mean 28.1%) and FD ranged from 1.4 to 4.1 (mean 2.6). Mean jitter, the percentage of jitter >55 micros, and the blocking percentage in 57 patients with definite or probable ALS were significantly higher than in patients with possible or suspected ALS. MRC scores of the EDC negatively correlated with mean jitter, the percentage of jitter >55 micros, blocking percentage, and FD.
Conclusions: SFEMG is the most sensitive tool for diagnosing definite or probable ALS. Increased jitter, blocking percentage, and FD can indicate the degree of immature collateral sprouts and motor end plates resulting from the progressive denervation and reinnervation associated with ALS, and may be helpful in evaluating prognosis.