Ipsilateral motor evoked potentials in a patient with unihemispheric cortical atrophy due to Rasmussen encephalitis

Abstract

The role of the ipsilaterally descending motor pathways in the recovery mechanisms after unilateral hemispheric damage is still poorly understood. Motor output reorganization was investigated in a 56-year-old male patient with acquired unilateral hemispheric atrophy due to Rasmussen encephalitis. In particular, the ipsilateral corticospinal pathways were explored using focal transcranial magnetic stimulation. In the first dorsal interosseous and wrist extensors muscles, the median amplitudes of the ipsilateral motor evoked potentials induced by transcranial magnetic stimulation in the patient were higher than those of 10 age-matched healthy control subjects. In the biceps brachii muscle, the median amplitudes of the ipsilateral motor evoked potentials were the second largest in the patient compared to the controls. This study demonstrated a reinforcement of ipsilateral motor projections from the unaffected motor cortex to the hemiparetic hand in a subject with acquired unihemispheric cortical damage.

Keywords: Rasmussen encephalitis; cortical atrophy; hemispheric damage; ipsilateral motor evoked potentials; ipsilateral motor pathways; motor cortex; transcranial magnetic stimulation.

Figure 1

MRI images in the patient with acquired unilateral hemispheric atrophy due to Rasmussen encephalitis. Coronal (A) and axial (B) brain MRI showed a left hemisphere atrophy, and a T2/Fluid-attenuated inversion recovery hyperintense signal in cortical and subcortical regions of the left frontal, temporal and occipital lobes. MRI: Magnetic resonance imaging.

Figure 2

Five consecutive electromyography recordings of ipsilateral motor evoked potentials in the active left first dorsal interosseous of the patient. Transcranial magnetic stimulation was applied to the left motor cortex at maximum stimulator output. It can be seen the marked trial-to-trial variability in motor evoked potential size and latency.

Figure 3

The MEPs for each participant and muscle. Different colors correspond to the muscle groups. MEP: Motor evoked potential; BB: biceps brachii; FDI: first dorsal interosseous; WE: wrist extensors.