title: Cortical dysfunction underlies disability in multiple sclerosis.
abstract: BACKGROUND
  Gray matter atrophy has been implicated in the development of secondary progressive multiple sclerosis (SPMS). Cortical function may be assessed by transcranial magnetic stimulation (TMS). Determining whether cortical dysfunction was a feature of SPMS could be of pathophysiological significance.
  
  
  OBJECTIVE
  Consequently, novel paired-pulse threshold tracking TMS techniques were used to assess whether cortical dysfunction was a feature of SPMS.
  
  
  METHODS
  Cortical excitability studies were undertaken in 15 SPMS, 25 relapsing-remitting MS patients (RRMS) and 66 controls.
  
  
  RESULTS
  Short interval intracortical inhibition (SPMS 3.0 ± 2.1%; RRMS 12.8 ± 1.7%, p < 0.01; controls 10.5 ± 0.7%, p < 0.01) and motor evoked potential (MEP) amplitude (SPMS 11.5 ± 2.2%; RRMS 26.3 ± 3.6%, p <0.05; controls 24.7 ± 1.8%, p < 0.01) were reduced in SPMS, while intracortical facilitation (SPMS -5.2 ± 1.9%; RRMS -2.0 ± 1.4, p < 0.05; controls -0.9 ± 0.7, p < 0.01) and resting motor threshold were increased (SPMS 67.5 ± 4.5%; RRMS 56.0 ± 1.5%, p < 0.01; controls 59.0 ± 1.1%, p < 0.001). Further, central motor conduction time was prolonged in SPMS (9.1 ± 1.2 ms, p < 0.001) and RRMS (7.0 ± 0.9 ms, p < 0.05) patients compared with controls (5.5 ± 0.2 ms). The observed changes in cortical function correlated with the Expanded Disability Status Scale.
  
  
  CONCLUSIONS
  Together, these findings suggest that cortical dysfunction is associated with disability in MS, and documentation of such cortical dysfunction may serve to quantify disease severity in MS.
authors.affiliation: Sydney Medical School Westmead, University of Sydney, Australia. s.vucic@neura.edu.au
authors.forename: Steve
authors.initials: S
authors.lastname: Vucic
authors.forename: Therese
authors.initials: T
authors.lastname: Burke
authors.forename: Kerry
authors.initials: K
authors.lastname: Lenton
authors.forename: Sudarshini
authors.initials: S
authors.lastname: Ramanathan
authors.forename: Lavier
authors.initials: L
authors.lastname: Gomes
authors.forename: Con
authors.initials: C
authors.lastname: Yannikas
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Kiernan
mesh_terms: D000328:Adult; D000368:Aged; D001284:Atrophy / Q000503:physiopathology; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000473:pathology* / Q000503:physiopathology; D020528:Multiple Sclerosis, Chronic Progressive / Q000473:pathology* / Q000503:physiopathology; D020529:Multiple Sclerosis, Relapsing-Remitting / Q000473:pathology* / Q000503:physiopathology; D009431:Neural Conduction; D009433:Neural Inhibition / Q000502:physiology; D050781:Transcranial Magnetic Stimulation