title: Split hand syndrome in amyotrophic lateral sclerosis: different excitability changes in the thenar and hypothenar motor axons.
abstract: BACKGROUND
  In amyotrophic lateral sclerosis (ALS), muscle wasting preferentially affects the abductor pollicis brevis (APB) and first dorsal interosseous over the abductor digit minimi (ADM), and this is termed 'split hand'. Previous axonal excitability studies have suggested increased nodal persistent sodium current and reduced potassium current in motor axons in ALS, but the extent of excitability changes in APB and ADM axons in ALS has never been compared.
  
  
  OBJECTIVE
  To elucidate the peripheral axonal pathophysiology of split hand.
  
  
  METHODS
  In both APB and ADM motor axons of 21 patients with ALS and 17 age-matched normal controls, threshold tracking was used to measure excitability indices such as strength-duration time constant (SDTC; a measure of persistent sodium current) and threshold electrotonus.
  
  
  RESULTS
  In normal controls, SDTC was significantly longer for APB than ADM axons, suggesting that axonal excitability is physiologically higher in APB axons. Compared with normal controls, patients with ALS had longer SDTC and greater threshold changes in depolarising threshold electrotonus in both APB and ADM axons. Furthermore, the difference in extent of SDTC prolongation between normal subjects and patients with ALS was greater in APB than ADM axons.
  
  
  CONCLUSIONS
  APB axons have physiologically higher excitability than ADM axons, and, in ALS, the hyperexcitability is more prominent in APB axons. Although cortical mechanisms would also be involved, more prominent hyperexcitability of APB axons may contribute to development of split hand, and the altered axonal properties are possibly associated with motor neuronal death in ALS.
authors: Department of Neurology, Graduate School of Medicine, Chiba University, Chiba, Japan.
authors: Kazumoto
authors: K
authors: Shibuya
authors: Sonoko
authors: S
authors: Misawa
authors: Saiko
authors: S
authors: Nasu
authors: Yukari
authors: Y
authors: Sekiguchi
authors: Satsuki
authors: S
authors: Mitsuma
authors: Minako
authors: M
authors: Beppu
authors: Shigeki
authors: S
authors: Ohmori
authors: Yuta
authors: Y
authors: Iwai
authors: Shoichi
authors: S
authors: Ito
authors: Kazuaki
authors: K
authors: Kanai
authors: Yasunori
authors: Y
authors: Sato
authors: Satoshi
authors: S
authors: Kuwabara
mesh_terms: D000328:Adult; D017668:Age of Onset; D000368:Aged; D000369:Aged, 80 and over; D000690:Amyotrophic Lateral Sclerosis / Q000150:complications* / Q000503:physiopathology; D001369:Axons; D003627:Data Interpretation, Statistical; D004558:Electric Stimulation; D055724:Electrophysiological Phenomena; D019054:Evoked Potentials, Motor; D005260:Female; D006225:Hand / Q000294:innervation* / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons; D012032:Refractory Period, Electrophysiological
keywords: Channels; Motor Neuron Disease; Neurophysiology; Neurophysiology, Motor