EVALUATION OF THE MOTOR CORTEX BY MAGNETIC STIMULATION IN PATIENTS WITH ALZHEIMER-DISEASE

Motor evoked potentials (MEPs) from abductor pollicis brevis (APE) and tibialis anterior (TA) muscles elicited by transcranial magnetic stim ulation of the motor cortex were studied in 15 patients with Alzheimer disease (AD). An abnormally higher MEP threshold in APE, frequently a ssociated with absence of the MEP in relaxed TA muscles, was found in 40% of patients, almost all of them in the more severe stage of the di sease. The MEP amplitude and averaged MEP/MAP ratio were reduced respe ctively by 20% and 26% in the APE muscle, and by 46.7% and 53.3% in th e TA muscle. The less frequent prolongation of the central conduction time (CCT) (20%) might reflect preservation of the impulse propagation along the surviving pyramidal fibers. In 63.6% of the patients the ce ntral silent period (cSP) duration in the APE muscle was shortened; th e mean value was significantly different between patients and controls . The results of this study suggest that loss and/or dysfunction of mo tor cortex neurones, including pyramidal cells and inhibitory interneu rones may occur in AD patients before clinical signs become apparent.