Cortical excitability distinguishes ALS from mimic disorders

ObjectiveThe diagnosis of amyotrophic lateral sclerosis (ALS) relies on stringent clinical criteria, resulting in diagnostic delay and inevitably the institution of appropriate therapy. Cortical hyperexcitability, as assessed by the novel threshold tracking transcranial magnetic stimulation (TTTMS) technique, appears as an early feature of ALS. Consequently, the present study assessed the diagnostic utility of threshold tracking TMS and developed algorithms to aid the diagnosis of ALS.MethodsProspective studies were undertaken on a cohort of 156 consecutive patients with neuromuscular symptoms (104 ALS and 52 lower motor neuron syndrome, non-ALS syndrome, NALS) and 62 healthy controls.ResultsShort-interval intracortical inhibition (SICI) was significantly reduced in ALS patients (2.4 ± 0.9%) compared to NALS (8.7 ± 0.8%, P < 0.0001) and controls (10.6 ± 0.8%, P < 0.0001). The MEP amplitude and intracortical facilitation were increased, while the cortical silent period duration was reduced in ALS, all indicative of cortical hyperexcitability. Analysis of receiver operating characteristic curves suggested that threshold tracking TMS distinguished ALS from NALS, with averaged (area under curve 0.76, P < 0.0001) and peak SICI 3 ms (area under curve 0.73, P < 0.0001) being the most robust diagnostic markers.ConclusionsThe presence of cortical hyperexcitability distinguishes ALS from mimic disorders.SignificanceThe threshold tracking TMS techniques may prove useful as a diagnostic investigation for ALS.

► This study addresses a diagnostic test for amyotrophic lateral sclerosis (ALS), reliably distinguishing ALS from mimic disorders. ► Using it, the diagnosis of ALS can be hastened by approximately 8 months, enabling implementation of specific treatments and recruitment into drug trials. ► The study provides insights into mechanisms underlying ALS.