Chapter 16 Preferential involvement of the fast conducting corticospinal tracts in patients with ALS

Publisher Summary Transcranial magnetic stimulation (TMS) at threshold intensity influences the discharge pattern of voluntarily activated single motor units (MUs), giving rise to a time locked synchronized firing called primary peak (PP). The analysis of the peristimulus time histograms (PSTHs) provides a physiologic measure of the corticospinal pathway in evaluating the pathophysiology of upper motor neuron diseases. This chapter discusses a study in which all amyotrophic lateral sclerosis (ALS) patients eventually fulfilled the EI-Escorial criteria for ALS. Based on the clinical findings at the time of the study, they were classified into groups of 26 typical ALS patients with upper and lower motor neuron signs, four patients with primary lateral sclerosis (ALS-PLS) with predominantly UMN and five patients with progressive muscular atrophy (ALS-PMA) with exclusive lower motor neuron signs. The threshold for cortical excitation was determined at rest using the oscilloscope display at a sensitivity of 50 μV/vertical division. In ALS with upper motor neuron (UMN), PSTHs frequently show double PPs and transcranial magnetic stimulation (TMS) elicits a high threshold motor evoked potentials (MEP) with a complex waveform. In the patients under observation, PP 2 usually matches the late component of complex MEP in latency. In contrast, normal subjects or patients without UMN show no such abnormalities.