Somatosensory evoked potentials in progressive supranuclear palsy.

We report median and digital nerve somatosensory evoked potentials (SEPs) in 14 patients with probable progressive supranuclear palsy (PSP) along with transcortical long-loop reflexes, motor evoked potentials, and auditory startle responses. Enlarged cortical responses were found in 14 median and 13 digital nerve SEP studies, while long-loop reflexes were increased in only one patient. All motor evoked potential studies were normal. Auditory startle responses were either absent or reduced in 11 patients. The observed neurophysiological abnormalities may reflect cortical hyperexcitability but are distinct from those in other disorders associated with giant SEPs, such as progressive myoclonus epilepsy. A number of groups reported widespread cortical changes in addition to the characteristic subcortical neurofibrillary degeneration in post-mortem confirmed PSP. However, clinical features reflecting cortical dysfunction such as ideomotor apraxia and cortical sensory loss are uncommon in classical PSP. Furthermore, frontal lobe dementia which is frequently present in PSP patients, is thought to be of subcortical origin resulting from striato-frontal deafferentation. We propose that cortical neurofibrillary pathology may lead to subclinical intracortical disinhibition accounting for the enlarged cortical SEPs in PSP.