T41. Ectopic impulse generation in peripheral nerve hyperexcitability syndromes and amyotrophic lateral sclerosis

Introduction Neuromuscular ultrasound has emerged as a non-invasive method for detecting fasciculations in the diagnosis of ALS. Of note, previous studies have suggested that ultrasound was a more reliable and sensitive tool in terms of detecting fasciculations in ALS and distinguishing from other conditions associated with fasciculations. However, there were no studies have investigated the difference in the distribution of fasciculations between ALS and the spectrum of peripheral nerve hyperexcitability syndrome using muscle ultrasound in a prospective and systematic fashion. The aim of the present study is to elucidate differences in the distribution and firing frequency of fasciculations between peripheral nerve hyperexcitability syndrome and amyotrophic lateral sclerosis (ALS) and to explore the generator site of fasciculations across these diseases. Methods Patients with Isaacs’ syndrome, cramp-fasciculation syndrome, benign fasciculation syndrome and Morvan syndrome were prospectively recruited as peripheral nerve hyperexcitability syndrome patients, with comparative studies undertaken in ALS patients. The distribution and firing frequency of fasciculations were calculated using muscle ultrasound recordings undertaken in 14 preselected muscles in each patient. Cortical excitability assessment was also performed by threshold tracking transcranial magnetic stimulation. Results 518 muscles from 37 peripheral nerve hyperexcitability syndrome patients and 756 muscles from 54 ALS patients were examined. Regarding the detection rate, 74% of muscles in ALS patients demonstrated fasciculations, compared with 34% of muscles in peripheral nerve hyperexcitability syndrome patients ( P P P P Conclusion A significant proportion of fasciculations in ALS may be influenced by changes in central excitability.