Ipsilateral silent period: a marker of callosal conduction abnormality in early relapsing-remitting multiple sclerosis?
OBJECTIVE
The corpus callosum (CC) is commonly affected in multiple sclerosis (MS). The ipsilateral silent period (iSP) is a putative electrophysiological marker of callosal demyelination. The purpose of this study was to re-assess, under recently established optimised protocol conditions [Jung P., Ziemann U. Differences of the ipsilateral silent period in small hand muscles. Muscle Nerve in press.], its diagnostic sensitivity in MS, about which conflicting results were reported in previous studies.


METHODS
ISP measurements (onset, duration, and depth) were obtained in the abductor pollicis brevis (APB) muscle of either hand in 49 patients with early relapsing-remitting MS (RRMS) (mean EDSS, 1.3). Standard central motor conduction times to the APB (CMCT(APB)) and tibial anterior muscles (CMCT(TA)), and magnetic resonance images (MRI) were also obtained.


RESULTS
ISP measurements showed a similar diagnostic sensitivity (28.6%) as CMCT(APB) (24.5%), while diagnostic sensitivities of CMCT(TA) (69.4%) and MRI of the CC (78.6%) were much higher. Prolongation of iSP duration was the most sensitive single iSP measure. ISP prolongation occurred more frequently when CMCT(APB) to the same hand was also prolonged (40.0% vs. 8.4%, p<0.0001). The correlation between iSP duration and CMCT(APB) was significant (Pearson's r=0.24, p<0.02), suggesting that iSP duration can be contaminated by demyelination of the contralateral corticospinal tract. ISP duration did not correlate with MRI abnormalities of the CC.


CONCLUSIONS
ISP measures are neither a sensitive nor a specific marker of callosal conduction abnormality in early RRMS.
Jung
Patrick
P
Department of Neurology, Johann Wolfgang Goethe-University, Schleusenweg 2-16, D-60528 Frankfurt am Main, Germany.
Beyerle
Astrid
A
Humpich
Marek
M
Neumann-Haefelin
Tobias
T
Lanfermann
Heinrich
H
Ziemann
Ulf
U
D000328:Adult; D003337:Corpus Callosum / Q000473:pathology / Q000503:physiopathology*; D018450:Disease Progression; D042241:Early Diagnosis; D004568:Electrodiagnosis / Q000379:methods; D005260:Female; D006225:Hand / Q000294:innervation / Q000503:physiopathology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology*; D020529:Multiple Sclerosis, Relapsing-Remitting / Q000175:diagnosis / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000503:physiopathology; D009413:Nerve Fibers, Myelinated / Q000473:pathology*; D009431:Neural Conduction / Q000502:physiology*; D011712:Pyramidal Tracts / Q000503:physiopathology; D011930:Reaction Time / Q000502:physiology; D050781:Transcranial Magnetic Stimulation / Q000379:methods