Fasciculation potentials and decremental responses in amyotrophic lateral sclerosis

Ultra-early amplitude decrement after repetitive nerve stimulation supports early neuromuscular junction injury in amyotrophic lateral sclerosis: a prospective cross-sectional study

The dying-back hypothesis holds that the damage to neuromuscular junctions and distal axons in amyotrophic lateral sclerosis occurs at the earliest stage of the disease. Previous basic studies have confirmed early damage to neuromuscular junctions, but it is difficult to obtain such evidence directly in clinical practice. In this prospective cross-sectional study, we recruited 22 patients with early amyotrophic lateral sclerosis with disease duration < 12 months and with clinical symptoms limited to the upper limbs. We also recruited 32 healthy controls. Repetitive nerve stimulation was performed, and patients were followed for 12 months. We found a significant change in the response to repetitive nerve stimulation in amyotrophic lateral sclerosis patients without spontaneous electromyographic activity. Patients that were prone to denervation had an increased decrement response of target muscles after repetitive nerve stimulation. These results suggest that changes in response to repetitive nerve stimulation may occur before denervation in amyotrophic lateral sclerosis patients. The damage to lower motor neurons is more obvious in patients with a higher percentage of repetitive never stimulation-related amplitude decrements. This study was approved by the Institutional Ethics Committee of Peking University Third Hospital (approval No. M2017198) on August 24, 2017.

Early Axonal Dysfunction of the Peripheral Nervous System Influences Disease Progression of ALS: Evidence From Clinical Neuroelectrophysiology

Objective: To assess the prognostic value of the decrement in compound muscle action potential amplitude within 12 months of symptom onset (CMAP-12 amplitude) for the survival of patients with amyotrophic lateral sclerosis (ALS).

Methods: Patients were stratified into 4 groups according to the decrement of the CMAP-12 amplitudes: normal (≥the lower limit of normal, LLN), mild (<LLN but ≥50% of LLN), moderate (<50% but ≥30% of LLN) and severe (<30% of LLN). All patients were followed up every 3 months. Survival was analyzed using the Kaplan-Meier method and Cox proportional hazards regression.

Results: A total of 149 patients were included in the analysis [90 males (60.4%); mean age at onset, 50.7 years]. The decrement of CMAP-12 amplitudes was normal in 24.2% of patients, mild in 22.1%, moderate in 15.4% and severe in 38.3%. Kaplan–Meier analysis showed there was a significant difference in the overall survival across the 4 groups (p < 0.05). Further pairwise comparisons identified significant differences in survival between the normal vs. the moderate group (p < 0.05) and the normal vs. the severe group (p < 0.01). There was a significant inverse correlation between the CMAP-12 amplitude and overall survival. Compared to that in the normal group, survival in the moderately and severely decreased groups was significantly shorter (HR 3.394, 95% CI 1.292–8.917, p = 0.013; and HR 4.732, 95% CI 2.032–11.017; p = 0.000, respectively).

Conclusions: Our results suggest that CMAP-12 amplitude could be a prognostic indicator of disease progression in ALS. More importantly, our findings provide clinical evidence for the viewpoint that early axonal dysfunction of the peripheral nervous system accelerates disease progression of ALS.

Reference values for the motor unit number index and the motor unit size index in five muscles

INTRODUCTION

Few reference values have been established for the motor unit number index (MUNIX) and motor unit size index (MUSIX). In this study we aimed to investigate the features of MUNIX in healthy individuals for five muscles.

METHODS

We measured the MUNIX in the right abductor pollicis brevis (APB), abductor digiti minimi (ADM), biceps brachii (BB), tibialis anterior (TA), and trapezius (TR) muscles.

RESULTS

The study enrolled 76 male and 74 female participants. The mean MUNIX and mean MUSIX of the right APB, ADM, BB, TA, and TR muscles were 191.0 ± 43.6, 179.1 ± 38.8, 179.7 ± 36.2, 152.1 ± 38.8, and 166.1 ± 40.7; and 60.4 ± 12.5, 59.3 ± 13.7, 43.8 ± 11.5, 41.3 ± 10.7, and 49.1 ± 15.2, respectively. MUNIX in these five muscles was inversely related to age.

DISCUSSION

The establishment of reference values for MUNIX and MUSIX in five muscles may help in monitoring the progression of neuromuscular diseases.