[Increased unilateral central motor tract excitability in a patient with corticobasal degeneration]

In a 64-year-old woman with a clinical diagnosis of corticobasal degeneration, a hyperexcitability of central motor tract was demonstrated. She had akinesia, regidity, myoclonic movement, hyperreflexia, forced grasping and clumusiness on the right extremities. The asymmetry of these symptoms was striking. Dopa therapy was not effective. On single photon emission computed tomography (SPECT), blood perfusion was reduced especially on the left side in the frontoparietal area. She had large C-reflex after the median nerve stimulation only on the affected side. The intensity threshold of motor evoked potential by stimulation on the left motor cortex was lower than that on the right motor cortex. Conditioning stimulation of the median nerve on the affected side, greatly increased MEP size as compared to those of normal subjects, at conditioning-test (C-T) intervals of 40-80 ms; whereas, stimulation on the contralateral side did not. On the other hand, SEP did not have a marked increase or asymmetry in size and SEP recovery curve showed no hyperexcitability. These results indicate there is a hyperexcitability of the central motor tract on the affected side.