MAGNETIC STIMULATION OF THE CORTICOSPINAL TRACTS IN PELIZAEUS-MERZBACHER DISEASE

To evaluate conduction abnormalities of the corticospinal tracts (CSTs ) in Pelizaeus-Merzbacher disease (PMD), magnetic stimulation at three levels was carried out in 3 buys with PMD aged between 9 and 12 years . They were all diagnosed as having a duplicated proteolipid protein g ene. The motor cortex and cervical spinal roots were stimulated with a round coil, whereas a double cone coil was used for brainstem stimula tion. Surface electromyographic (EMG) recording was performed on the f irst dorsal interosseous muscles. Despite a normal EMG response to cer vical stimulation, magnetic shock of the motor cortex elicited no EMG activity, even in the case with less motor symptoms. This discrepancy between the electrophysiological and clinical findings is likely due t o slowing conduction, which reduces the temporal summation of multiple descending volleys magnetically elicited. A partial conduction block may also occur because of the lack of an EMG response to brain-stem st imulation. Thus, we speculated that the spastic paresis in PMD is asso ciated with both slowing conduction and a partial conduction bloch in the CSTs. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.