Y. Terao et al., MOTOR CORTICAL REFLEX MYOCLONUS - A CASE-STUDY WITH MEG, Electroencephalography and clinical neurophysiology, 102(6), 1997, pp. 505-511
Cortical reflex myoclonus usually depends for its generation on the hy
perexcitability of sensory cortex, which manifests itself as an enhanc
ed somatosensory evoked potential (SEP). A 25-year-old female, present
ing with involuntary jerky dorsiflexion of the left foot, was found to
have cortical reflex myoclonus which was aggravated during intended m
ovements. The jerks were also elicited by electrical stimulation of th
e posterior tibial nerve, although the SEP evoked by the same stimulus
was normal in latency and amplitude. Both the spontaneous spikes and
the premyoclonus spike demonstrated by jerk-locked back averaging were
localized to the superior frontal gyrus, just anterior to the paracen
tral sulcus. Paired-pulse magnetic stimulation disclosed lack of inhib
ition in the right hemisphere leg motor area, whereas the Excitability
of sensory cortex as studied by paired SEP testing was normal. This s
uggests that the myoclonus was caused mainly by enhanced excitability
of the motor cortex and that this alone was enough for the production
of long loop reflexes. We propose to designate this type of cortical m
yoclonus as motor cortical reflex myoclonus. It is generated in the mo
tor cortex, but is at the same time stimulus-sensitive. (C) 1997 Elsev
ier Science Ireland Ltd.