Transcranial magnetic stimulation to monitor disease progression in ALS: a review

Abstract

Objectives: Transcranial magnetic stimulation (TMS) is a technique to assess motor system function which has been used extensively in amyotrophic lateral sclerosis (ALS). Information on the changes during disease progression is scarce. We aimed to collect this information in a single source. Methods: Literature search tools and personal searching were used to find relevant data. Results: In ALS, 1. Motor threshold tends to increase in hand muscles over disease progression. 2. Central motor conduction time is not a sensitive measurement. 3. Motor evoked potential amplitude decreases, in particular in lower limbs. 4. Primary peak from the peristimulus time histogram (PSTH) reduces in amplitude and synchronicity, but longer duration. 5. Inhibitory responses using PSTH are more pronounced over the disease course. 6. In hand muscles central silent period (CSP) is shorter early in the disease but increases with time. 7. Short inhibitory cortical interval (SICI) is abnormal in the very early disease stage and shows greater abnormality over time. 8. Area and volume in cortical maps of hand muscle decrease markedly with disease progression. Discussion: TMS studies evaluating changes over time in ALS suggest that measuring interneuronal inhibitory dysfunction is a promising method to track progression but motor amplitude and cortical maps should be investigated further. Conclusions: Available TMS studies quantifying central motor dysfunction are insufficient to propose a single physiological measurement for evaluating progression in ALS.

Keywords:

• Amyotrophic lateral sclerosis
• disease progression
• monitoring
• neurophysiological markers
• transcranial magnetic stimulation

Declaration of interest

No potential conflict of interest was reported by the author(s).