Abstract
Background: While the association between motor-evoked potential (MEP) abnormalities and motor deficit is well established, few studies have reported the correlation between MEPs and signs of pyramidal tract dysfunction without motor weakness. We assessed MEPs in patients with pyramidal signs, including motor deficits, compared to patients with pyramidal signs but without weakness. Methods: Forty-three patients with cervical spondylotic myelopathy (CSM) were dichotomized into 21 with pyramidal signs including motor deficit (Group 1) and 22 with pyramidal signs and normal strength (Group 2), and both groups were compared to 33 healthy controls (Group 0). MEPs were bilaterally recorded from the first dorsal interosseous and tibialis anterior muscle. The central motor conduction time (CMCT) was estimated as the difference between MEP latency and peripheral latency by magnetic stimulation. Peak-to-peak MEP amplitude and right-to-left differences were also measured. Results: Participants were age-, sex-, and height-matched. MEP latency in four limbs and CMCT in the lower limbs were prolonged, and MEP amplitude in the lower limbs decreased in Group 1 compared to the others. Unlike motor deficit, pyramidal signs were not associated with MEP measures, even when considering age, sex, and height as confounding factors. Conclusions: In CSM, isolated pyramidal signs may not be associated, at this stage, with MEP changes.
Highlights
Motor cortex excitability and corticospinal conduction can be noninvasively probed in vivo and in “real time” by recording motor-evoked potentials (MEPs) in response to transcranial magnetic stimulation (TMS) [1]
MEP latency and central motor conduction time (CMCT) are viewed as measures of cortical–spinal myelination, whereas MEP amplitude is viewed as an index of the integrity of the neuronal axons from motor cortical areas to spinal motoneurons [2]
Group 2 showed a similar distribution of the pyramidal signs, but without any clinically detectable motor deficit (MRC 5 in all muscular districts)
Summary
Motor cortex excitability and corticospinal conduction can be noninvasively probed in vivo and in “real time” by recording motor-evoked potentials (MEPs) in response to transcranial magnetic stimulation (TMS) [1]. On the basis of these principles, MEP recording allows for the objective, reproducible, and painless assessment of the central motor pathways, including the activation status of facilitatory and inhibitory neuronal networks [3] and interhemispheric functioning [4]. Since it was first introduced [5], diagnostic TMS has been applied in almost all neurological disorders and systemic diseases with neurological involvement [6], showing a high sensitivity in the detection of corticospinal tract lesions [7] and allowing preclinical diagnosis [8,9,10] and disease monitoring [11].
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