The electrophysiological methods in the early diagnosis of amyotrophic lateral sclerosis: The importance of the fasciculation potentials

ALS is a progressive and fatal neurodegenerative disease with loss of motor neurons in the primary motor cortex, brainstem and spinal cord. The presence of both lower and upper motor neuron findings is a distinguishing feature. These findings are searched by clinical examination and electrophysiological methods. Fasciculations indicating the lower motor neuron involvement are among the early signs of the disease. As determined by examination, they appear as sudden irregular motor unit discharges at rest on needle electromyography. Fasciculations are not ALS-specific and do not always indicate a pathological condition. However, their significance in the early diagnosis of ALS was better understood with the adoption of Awaji criteria in 2006. It is therefore important to elaborate the peculiarities of ALS fasciculations. The aim of this study was to show which electrode would be more suitable for the investigation of fasciculation potentials and to test whether the fasciculating motor units were involved in the voluntary muscle. Twenty patients with definite ALS according to Awaji criteria were enrolled in the study. After routine conduction studies and needle electromyography, fasciculation potentials were recorded by bipolar saddle electrode in the first dorsal interosseous muscle for 2 minutes. Then fasciculation potentials were recorded in the same muscle by using concentric needle electrodes (37 mm) at 3 different points with a single skin insertion at each position for 2 minutes and total for 6 minutes. Motor unit potentials recruited in voluntary muscle contraction were recorded for quantitative MUP analysis at the needle recording points. The data were then analyzed off-line. Fasciculations were classified according to their shapes as simple, complex and combined. The MUPs recorded by quantitative MUP analysis were searched in the fasciculating MUPs. The ages of the patients ranged from 35 to 72 years (mean 54 years). The female to male ratio was 5:15. Thirteen patients had spinal onset and 7 had bulbar onset. The number of superficial and needle electrodes recorded was noted for each patient. Totally 737 fasciculatory potentials were recorded by superficial electrodes and 2141 by needle electrodes. Fasciculations recorded by superficial electrodes did not provide sufficient information in terms of amplitude, duration and phase, whereas those recorded by needle electrodes could be classified as simple, complex and combined. Of all fasciculations, simple fasciculations were the most common: 57%. The second most frequent fasciculations were complex ones: 36%. The most rare fasciculations were combined: 7%. The total fasciculation potentials observed at the needle registration points were significantly higher than those recorded on the surface (p <0.00). However, taking into account the positions where the needle registers the least number of fasciculation potential, superficial recording noticed a higher number of fasciculations (p <0.016). In the early stages of the disease and in the cases with bulbar onset, fasciculation potentials were observed more intensely before other denervation potentials. Finally, it was investigated whether there were fasciculating MUP among the MUPs recorded by quantitative MUP analysis.In the 8 of 20 patients voluntary activated FP was observed. However, this participation was very low. At least 0.44% and most 4.4% of the fasciculating MUPs were recruited voluntary. All of them were simple in shape. In the light of the data obtained in our study, it was concluded that superficial electrode fasciculation recording can be used as a rapid screening method, but it is still more appropriate to use needle electrode, and it is necessary to give enough time to the patient when searching for fasciculation with needle electrode. It was concluded that low voluntary recruitment rate of fasciculating motor units could be a conclusion of the disturbance in the upper motor neuron or in the axon hillock of lower motor neuron. The fact that all the voluntary recruited fasciculations were simple in shape was consistent with the literature. In addition, monitoring of fasciculations without positive spike and fibrillation potentials in patients with bulbar onset and early period was consistent with the fasciculation potential characteristics described in Awaji criteria. It was emphasized one more time that Awaji criteria should be applied for the early diagnosis of ALS. Key words: ALS, Fasciculation Potential, Awaji criteria, Early Diagnosis