O-MN002. Assessment of upper motor neuron function utilizing threshold tracking transcranial magnetic stimulation in amyotrophic lateral sclerosis

Abstract

Introduction . Upper motor neuron signs are mainly assessed by clinical examinations. Threshold tracking transcranial magnetic stimulation (TT-TMS) can precisely investigate motor cortical function and has been reported as a diagnostic marker in amyotrophic lateral sclerosis (ALS). The correlation between TT-TMS and clinical and neurophysiological findings were examined. Methods . TT-TMS was performed in 30 ALS patients and 26 healthy controls (HC), measured in the abductor pollicis brevis (APB) muscle. Clinical factors, such as age, gender, disease duration, site of onset, upper motor neuron (UMN) sign scores and ALS functional rating scale revised (ALSFRS-R) and a neurophysiological index, such as compound muscle action potential (CMAP) amplitude, measured in the APB muscle, were analyzed with TT-TMS findings. Results . Of 30 patients, 13 were male, and 10 were bulbar onset. The mean age was 69 years old, and the mean disease duration was 19 months. Averaged short interval intracortical inhibition (SICI) (1-7 ms) was decreased in ALS (p < 0.01), compared with HC. Averaged SICI (1-7 ms) was not related to age, gender, disease duration, site of onset, UMN sign scores, ALSFRS-R and CMAP amplitudes. Decreased SICI was unveiled even in 4 patients, without evident upper motor neuron signs. Conclusion . TT-TMS found motor cortical dysfunction in ALS, but the relationship between SICI and UMN signs was not evident. Progress of cortical hyperexcitability and pyramidal tract lesion may not be parallel in ALS. Additionally, muscle atrophies might hamper detection of UMN signs. Further studies are necessary to discuss usefulness of TT-TMS as a UMN sign marker in ALS.