title: Cortical hyperexcitability and the split-hand plus phenomenon: pathophysiological insights in ALS.
abstract: Preferential involvement of thenar muscles compared to flexor pollicis longus (FPL), termed 'the split-hand plus sign', appears to be a clinical feature of amyotrophic lateral sclerosis (ALS). In an attempt to understand the pathophysiological mechanisms underlying this clinical phenomenon, threshold tracking transcranial magnetic stimulation techniques were utilized to assess whether cortical mechanisms may be a significant contributing influence. Cortical excitability studies were undertaken on 17 ALS patients, with motor evoked potentials (MEP) recorded from thenar muscles and FPL. Split-hand plus index (SHPI) was derived by dividing motor amplitudes recorded over APB with those recorded over FPL. Results showed the SHPI was significantly reduced in ALS (SHPIALS 0.87 ± 0.12; SHPICONTROLS 1.7 ± 0.2, p < 0.001). Cortical studies disclosed significant increases in MEP amplitudes recorded over thenar muscles (p < 0.05) but not FPL (p = 0.11), and were significantly correlated with the SHPI (R = -0.83, p < 0.01). The cortical silent period duration was reduced from thenar muscles (p < 0.01). Although there was a ubiquitous reduction in short-interval intracortical inhibition (APB, p < 0.01; FPL < 0.05), this reduction was more prominent over the thenar muscles. In conclusion, findings from the present study suggest that cortical dysfunction in the form of hyperexcitability contributes to the pathophysiological basis of the split-hand plus sign in ALS.
authors.affiliation: Hallym University College of Medicine , Korea.
authors.forename: Jong Seok
authors.initials: JS
authors.lastname: Bae
authors.forename: Parvathi
authors.initials: P
authors.lastname: Menon
authors.forename: Eneida
authors.initials: E
authors.lastname: Mioshi
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Kiernan
authors.forename: Steve
authors.initials: S
authors.lastname: Vucic
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000690:Amyotrophic Lateral Sclerosis / Q000150:complications* / Q000473:pathology*; D002540:Cerebral Cortex / Q000503:physiopathology*; D013181:Cortical Spreading Depression / Q000502:physiology; D004569:Electroencephalography; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006225:Hand / Q000294:innervation / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000294:innervation / Q000503:physiopathology*; D050781:Transcranial Magnetic Stimulation
keywords: Abductor pollicis brevis; TMS; amyotrophic lateral sclerosis; cortical excitability; flexor pollicis longus