[A study of magnetic stimulation in patients with clinically diagnosed corticobasal degeneration]

Magnetic stimulation (MS) was performed in 9 patients with clinically diagnosed corticobasal degeneration (CBD), 10 patients with Parkinson's disease (PD) (under L-dopa therapy) and 10 age-matched healthy subjects (HS). Motor evoked potentials (MEPs) were recorded from the abductor pollicis brevis muscle (APB) in response to cortical stimulation and cervical stimulation (C7). In all patients with CBD, the duration of inhibitory period (IP), which was a transient suppression of muscle action potentials following MEPs by cortical stimulation, was significantly shorter than that in PD and HS. In 4 patients with CBD who presented with focal and distal myoclonus of one limb, long latency reflexes following electrical stimulation of the median nerve showed C-reflex, which had a latency of about 40 ms, but a giant SEP and a jerk-locked cortical potential were not demonstrated. With cervical MS, these 4 patients also showed long-latency (about 30 ms) evoked potentials (LEPs), which were much greater in latency from cervical stimulation-induced MEPs (cervical MEPs). LEPs may be mediated via a transcortical loop, because the sum of the latency of C-reflex and compound muscle action potential approximates that of LEP and cervical MEP. In patients with CBD, these findings suggest disturbance within the basal ganglia-thalamocortical motor circuit and a damage of the motor cortices including the primary motor cortex, premotor cortex and supplementary motor cortex.