Utility of single fiber electromyography in the differential diagnosis of amyotrophic lateral sclerosis and cervical spondylosis

Abstract

Objective To assess the utility of single fiber electromyography (SFEMG) in the differential diagnosis of amyotrophic lateral sclerosis (ALS) and cervical spondylotic radiculopathy and myelopathy. Methods SFEMG was performed in extensor digitorum communis muscles (EDC) of 3 groups of patients, including 61 ALS patients with findings of cervical spendylosis on MRI, 59 ALS patients with normal MRI of cervical spine, and 55 patients with cervical spendylotic radiculopathy and myelopathy. The parameters of SFEMG between different groups were compared. Results The mean jitter was (81.2± 25.9), (91.6 ± 32. 4) and (40. 9 ± 11.8) μ in ALS patients with finding of cervical spondylosis on MRI, ALS patients with normal MRI of cervical spine, and patients with cervical spondylosis respectively. M50 of the percentage of jitter >55 μs was 73%, 80% and 5% in the 3 groups respectively. M50 of the percentage of block was 10%, 20% and 0 in the 3 groups respectively. Fiber density was 2.9±0.5, 2.9±0.6 and 2. 4 ± 0. 6 in the 3 groups respectively. There was no significant difference in those parameters of SFEMG between the ALS with findings of cervical spondysosis and those with normal MRI. There was significant difference in those parameters of SFEMG between the patients with ALS (the mean jitter: (86. 3± 29. 6) μs; M50 of the percentage of jitter > 55 μs: 80% ; M50 of the percentage of block: 14% ; fiber density: 2. 9±0. 5) and those with cervical spondylosis (t = 14.49, Z = 8.96, 7. 68,t = 5. 83, all P = 0. 000). In 18 patients with ALS, conventional EMG studies showed active and chronic denervation in only 1 region at the first visit. SFEMG was performed in EDC which had normal Medical Research Council Scale and EMG. SFEMG showed increased fiber density in 16 patients, increased jitter in 13 patients and impulse block in 6 patients. Conclusion SFEMG shows significantly increased jitter and block in ALS whether there is MRI findings of cervical spondysosis or not, which can help to differentiate ALS from cervical spondysotic radiculopathy and myelopathy. Key words: Amyotrophic lateral sclerosis; Cervical spondylosis; Electromyography; Diagnosis; differential