[Corticobasal degeneration and progressive supranuclear palsy--differentiation by somatosensory-evoked potentials]

It is by no means easy to make an early differential diagnosis between corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP), because both disorders occasionally show similar clinical features such as parkinsonism, supranuclear gaze palsy, or dementia. In the present study, we studied somatosensory-evoked potentials (SEPs) in 4 CBD and 8 PSP patients. SEPs after median nerve stimulation (0.2 ms square wave delivered with a frequency of 1 Hz) were recorded from bilateral parietal and midfrontal electrodes. Latencies of identifiable peaks and the inter-peak amplitudes were measured, and a comparison was made between the two disorders. Both latencies and amplitudes of all the identified peaks showed no statistical difference between the two disorders. To reveal an inter-hemispheric difference of the amplitude, we calculated the asymmetry index: the amplitude of the more affected side/the sum of the amplitudes of both sides. In CBD patients, an asymmetry index of P1N2 amplitude was found to be decreased significantly. The asymmetric appearance of this part of SEPs may be helpful for early differential diagnosis between CBD and PSP.