LATENCY AND DURATION OF THE MUSCLE SILENT PERIOD FOLLOWING TRANSCRANIAL MAGNETIC STIMULATION IN MULTIPLE-SCLEROSIS, CEREBRAL-ISCHEMIA, AND OTHER UPPER MOTONEURON LESIONS
Ba. Haug et B. Kukowski, LATENCY AND DURATION OF THE MUSCLE SILENT PERIOD FOLLOWING TRANSCRANIAL MAGNETIC STIMULATION IN MULTIPLE-SCLEROSIS, CEREBRAL-ISCHEMIA, AND OTHER UPPER MOTONEURON LESIONS, Neurology, 44(5), 1994, pp. 936-940
In muscles with sustained voluntary contraction, EMG activity is trans
iently inhibited after transcranial magnetic stimulation. We recorded
this postexcitatory silent period (SP) at 1.5 times individual stimulu
s threshold level from the first dorsal interosseus muscle in 65 neuro
logic patients aged 11 to 80 years. When compared with 20 healthy volu
nteers and a subgroup of patients with peripheral neurologic condition
s not affecting the tested pathways, the SP was significantly longer o
n the paretic side in cerebral ischemia (p < 0.001) and chronic inflam
matory CNS diseases, such as multiple sclerosis or neurosarcoidosis (p
< 0.01). There was a similar tendency in pyramidal tract lesions due
to CNS tumors and spinal cord trauma. In lesser degrees of paresis, SP
duration is more sensitive than central motor conduction time (CMCT),
but its specificity awaits further evaluation. SP is dependent on the
integration of motor excitatory and inhibitory pathways and, possibly
, sensorimotor reflex systems. In contrast to SP duration, which prove
d to be an independent variable giving supplementary information over
the usual CMCT measurement, SP onset latency correlates well with CMCT
and peripheral nerve conduction slowing, as in polyradiculoneuritis.