Abstract
Triad conditioned facilitation induced by transcranial magnetic stimulation (TMS) in healthy individuals has been proposed to reflect the intrinsic 40 Hz piper rhythm of the motor cortex. However, it is unclear if triad conditioned facilitation is influenced by degeneration of the motor cortex. Amyotrophic lateral sclerosis (ALS) is characterized among others by degeneration of the motor cortex. We therefore hypothesized that triad conditioned facilitation may be impaired in ALS patients. Moreover, we hypothesized that this triad conditioning paradigm may be helpful to differentiate ALS from cervical myelopathy, an important differential diagnosis. In 10 patients with ALS and 9 patients with cervical myelopathy serving as disease control, we compared single pulse conditioned intracortical inhibition (ICI), intracortical facilitation (ICF) and also triad conditioned facilitation at various interstimulus intervals (ISI) between 3 ms and 50 ms. There were no differences in ICI and ICF between both groups. Both groups also showed similar triad conditioned facilitation at 10 ms ISI. Patients with cervical myelopathy showed normal triad conditioned facilitation at 25 ms ISI comparable to healthy subjects. In contrast ALS patients showed no triad conditioned facilitation at 25 ms. The absence of triad conditioned facilitation at 25 ms ISI in ALS patients may represent changes of the intrinsic rhythm of the motor cortex probably caused by cortical degeneration. Triad conditioned TMS may be a valuable tool to differentiate ALS patients from patients with cervical myelopathy.
Published Version
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