Neurology. 2026 Jul 28;107(2):e218273. doi: 10.1212/WNL.0000000000218273. Epub 2026 Jul 6.
ABSTRACT
BACKGROUND AND OBJECTIVES: The origin of fasciculation potentials (FPs) in the early stages of amyotrophic lateral sclerosis (ALS) remains a subject of debate. We investigated the role of the motor cortex in FP generation by comparing resting FP frequency in the first dorsal interosseous (FDI) muscle before and after motor cortex inhibition induced by continuous theta-burst stimulation (cTBS).
METHODS: We studied patients with early-stage ALS (G1) and a disease-control group (G2) comprising individuals with chronic lower motor neuron (LMN) disorders or benign fasciculation syndrome without upper motor neuron (UMN) involvement. Inclusion required a right FDI strength of MRC grade 4+ or 5. At baseline, we recorded FP frequency and amplitude in the right FDI (3 replicates) and the motor evoked potential (MEP) amplitude. These measures were repeated immediately after cTBS-induced corticomotor inhibition. Statistical significance was set at p < 0.05.
RESULTS: Twenty-two patients with ALS (14 men; median age 65.5 years; 72.7% spinal onset) were included, with a median disease duration of 6.4 months and a mean ALSFRS-R score of 44. The control group (G2) consisted of 11 participants. Notably, 50% of the ALS cohort showed no neurogenic features on needle EMG of the right FDI at enrollment. Baseline peripheral and cortical amplitudes and left hemisphere motor thresholds were comparable between groups. After cTBS, MEP amplitudes decreased significantly in both G1 (0.93 vs 0.50 mV, p = 0.02) and G2 (1.23 vs 0.38 mV, p = 0.02). However, a significant reduction in FP frequency (39.5%) occurred only in the ALS group (0.43 vs 0.26 Hz, p < 0.001), whereas no change was observed in G2 (0.60 vs 0.77 Hz, p = 0.14). Patients with ALS with a normal FDI EMG demonstrated an even greater reduction in FP frequency (54.5%). FP amplitudes remained stable across both groups after cTBS.
DISCUSSION: Our findings indicate that in early ALS, LMN excitability is significantly modulated by descending corticospinal input. The reduction in FP frequency after cortical inhibition suggests that FPs in early ALS are driven by a combination of both UMN and LMN hyperexcitability, distinguishing them from fasciculations in other neurogenic disorders.
PMID:42407013 | DOI:10.1212/WNL.0000000000218273
