[Primary progressive limb-kinetic apraxia: a case report with an electrophysiological study].

We report a 53-year-old right handed woman with a 5-year history of slowly progressive clumsiness of her right hand. Neurologic symptoms was otherwise unremarkable except for mild dysarthria. Brain CT and MRI revealed a focal atrophic change in the left precentral gyrus. She was thought to have the primary progressive limb-kinetic apraxia. Electrophysiological studies were performed to explore physiologic mechanism of her apraxia. Surface EMG revealed co-contraction of antagonistic muscles in her right upper extremity with rhythmic myoclonic discharges. C-reflex was positive after median nerve stimulation only on the affected side. SEPs elicited by the median nerve stimulation were not enlarged and the SEP recovery curves showed no abnormal facilitation or inhibition. In addition, the premyoclonus spike was demonstrated by Jerk-locked averaging. Transcranial magnetic stimulation using double pulse paradigm revealed a decrease in the level of cortico-cortical inhibition on the motor cortex in the affected side. Median nerve stimulation given prior to the transcortical magnetic stimulation on the size of the magnetic evoked potential (MEP) revealed abnormal facilitations on the affected side, especially at conditioning-test interval of 60-80 ms. Therefore, our results indicate increase in the excitability of motor cortical neurons in primary progressive limb-kinetic apraxia, likely due to a decreased excitability of cortico-cortical inhibitory mechanism as a result of focal degeneration of cortical neurons.