Split hand syndrome in amyotrophic lateral sclerosis: Different excitability changes in the thenar and hypothenar motor axons

Kazumoto Shibuya, Sonoko Misawa, Saiko Nasu, Yukari Sekiguchi, Satsuki Mitsuma, Minako Beppu, Shigeki Ohmori, Yuta Iwai, Shoichi Ito, Kazuaki Kanai, Yasunori Sato, Satoshi Kuwabara

Research output: Contribution to journalArticlepeer-review

76 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)969-972
Number of pages4
JournalJournal of Neurology, Neurosurgery and Psychiatry
Issue number9
Publication statusPublished - 2013 Sept
Externally publishedYes

ASJC Scopus subject areas

  • Surgery
  • Clinical Neurology
  • Psychiatry and Mental health


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