title: Proportional recovery after stroke depends on corticomotor integrity.
abstract: OBJECTIVE
  For most patients, resolution of upper limb impairment during the first 6 months poststroke is 70% of the maximum possible. We sought to identify candidate mechanisms of this proportional recovery. We hypothesized that proportional resolution of upper limb impairment depends on ipsilesional corticomotor pathway function, is mirrored by proportional recovery of excitability in this pathway, and is unaffected by upper limb therapy dose.
  
  
  METHODS
  Upper limb impairment was measured in 93 patients at 2, 6, 12, and 26 weeks after first-ever ischemic stroke. Motor evoked potentials (MEPs) and motor threshold were recorded from extensor carpi radialis using transcranial magnetic stimulation, and fractional anisotropy (FA) in the posterior limbs of the internal capsules was determined with diffusion-weighted magnetic resonance imaging.
  
  
  RESULTS
  Initial impairment score, presence of MEPs and FA asymmetry were the only predictors of impairment resolution, indicating a key role for corticomotor tract function. By 12 weeks, upper limb impairment resolved by 70% in patients with MEPs regardless of their initial impairment, and ipsilesional rest motor threshold also resolved by 70%. Resolution of impairment was insensitive to upper limb therapy dose.
  
  
  CONCLUSIONS
  These findings indicate that upper limb impairment resolves by 70% of the maximum possible, regardless of initial impairment, but only for patients with intact corticomotor function. Impairment resolution seems to reflect spontaneous neurobiological processes that involve the ipsilesional corticomotor pathway. A better understanding of these mechanisms could lead to interventions that increase resolution of impairment above 70%.
authors.affiliation: Center for Brain Research, University of Auckland, Auckland, New Zealand.|Department of Sport & Exercise Science, University of Auckland, Auckland, New Zealand.
authors.forename: Winston D
authors.initials: WD
authors.lastname: Byblow
authors.affiliation: Center for Brain Research, University of Auckland, Auckland, New Zealand.|Department of Medicine, University of Auckland, Auckland, New Zealand.
authors.forename: Cathy M
authors.initials: CM
authors.lastname: Stinear
authors.affiliation: Center for Brain Research, University of Auckland, Auckland, New Zealand.|Department of Medicine, University of Auckland, Auckland, New Zealand.
authors.forename: P Alan
authors.initials: PA
authors.lastname: Barber
authors.affiliation: Center for Brain Research, University of Auckland, Auckland, New Zealand.|Department of Medicine, University of Auckland, Auckland, New Zealand.|Bionics Institute of Australia, Melbourne, Australia.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Petoe
authors.affiliation: Center for Brain Research, University of Auckland, Auckland, New Zealand.|Department of Medicine, University of Auckland, Auckland, New Zealand.
authors.forename: Suzanne J
authors.initials: SJ
authors.lastname: Ackerley
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002545:Brain Ischemia / Q000503:physiopathology / Q000534:rehabilitation; D002540:Cerebral Cortex / Q000503:physiopathology*; D015331:Cohort Studies; D038524:Diffusion Magnetic Resonance Imaging; D004525:Efferent Pathways / Q000503:physiopathology; D004576:Electromyography; D019054:Evoked Potentials, Motor; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000503:physiopathology*; D017063:Outcome Assessment, Health Care; D020127:Recovery of Function / Q000502:physiology*; D020521:Stroke / Q000503:physiopathology*; D000071939:Stroke Rehabilitation; D050781:Transcranial Magnetic Stimulation; D034941:Upper Extremity / Q000503:physiopathology*