title: Interhemispheric inhibition in patients with multiple sclerosis.
abstract: OBJECTIVE
  A single focal magnetic stimulus applied to the motor cortex of normal subjects can suppress ongoing voluntary electromyographic activity in ipsilateral small hand muscles. This inhibition is mediated from one motor cortex to the contralateral side via a transcallosal pathway.
  
  
  METHODS
  We have investigated transcallosal inhibition in 24 patients with definite multiple sclerosis (MS) and in 24 healthy volunteers. A focal magnetic stimulus was applied to the hand area of the motor cortex and the onset latency of the inhibition of the ongoing EMG activity of the ipsilateral first dorsal interosseus muscle was evaluated. Cortico-motor conduction time to the same muscle was revealed, using a magnetic stimulus over the contralateral motor cortex. The difference between these values was calculated as transcallosal conduction time. Cerebral magnetic resonance imaging (MRI) scans including sagittal T2-weighted images were performed in 18 patients.
  
  
  RESULTS
  The depth of inhibition (maximal inhibition as percentage of the baseline EMG) in the MS patients was comparable to normal values, but the transcallosal conduction time was significantly delayed (patients 17.2 +/- 6.4 ms; normal subjects 12.2 +/- 2.6 ms; P < 0.001). The duration of the inhibition was significantly prolonged in MS patients (patients 47.9 +/- 20.9 ms; normal subjects 38.9 +/- 10.1 ms; P = 0.02). Transcallosal conduction time was delayed in 11 (46%) of 24 patients, compared with normal subjects. It exceeded the normal range (mean +/- 2.5 SD) in one normal subject (specificity 96%). No correlation could be found between the size or extent of the lesions obtained from the MRI scan and the onset latency or the depth of the inhibition.
  
  
  CONCLUSIONS
  We conclude that conduction over transcallosal connections is significantly slower in patients with MS.
authors.affiliation: Department of Neurology, University Hospital, RWTH Aachen, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Boroojerdi
authors.forename: M
authors.initials: M
authors.lastname: Hungs
authors.forename: M
authors.initials: M
authors.lastname: Mull
authors.forename: R
authors.initials: R
authors.lastname: Töpper
authors.forename: J
authors.initials: J
authors.lastname: Noth
mesh_terms: D000328:Adult; D000368:Aged; D002540:Cerebral Cortex / Q000503:physiopathology*; D003337:Corpus Callosum / Q000502:physiology; D004185:Disability Evaluation; D004574:Electromagnetic Fields; D004576:Electromyography; D004594:Electrophysiology; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006225:Hand / Q000294:innervation / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology