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The ‘split-hand syndrome’1 2 is well known as a characteristic sign of amyotrophic lateral sclerosis (ALS), which means that the first dorsal interosseous (FDI) and the abductor pollicis brevis (APB) muscles are preferentially affected in patients with ALS, with relative sparing of the abductor digiti minimi (ADM) muscle. The ‘split-hand plus sign’ has been also reported, in which the flexor pollicis longus (FPL) muscle is preserved compared with APB.3 The first author found another clinical sign of selective involvement in ALS, the ‘split-finger syndrome’. This means that the first flexor digitorum profundus (FDP1) muscle, that is, FDP to the index finger, is more severely affected than the fourth flexor digitorum profundus (FDP4) muscle, FDP to the little finger. We documented this feature by a retrospective study, comparing its sensitivity with the split-hand and split-hand plus syndromes.
Subjects were enrolled from our Electromyography (EMG) database from 2015 to 2018. Patients having the diagnosis with ALS were extracted and their clinical and EMG records were reviewed. The inclusion criteria were as follows: (1) the patient was diagnosed with ALS at our initial evaluation from clinical and EMG findings; (2) Medical Research Council (MRC) scales of FDP1, FDP4, FDI, APB, ADM and FPL were evaluated by the first author (MS); (3) follow-up information confirmed the diagnosis of ALS by the attainment of endpoints (death, artificial ventilation, tracheostomy or gastrostomy) or definite relentless progression that could not be explained by other reasons. Patients whose final diagnosis proved to …
Contributors All authors made substantial contributions to the manuscript and approved the final draft. KT, YH, KH and MS collected the data. SK made important suggestions regarding the figure and text. MS designed the whole study, wrote the first draft, made statistical analyses and finalised the manuscript.
Funding This study was partly supported by Grants-in-Aid for Scientific Research (19K07966) from the Ministry of Education, Science, Sports and Culture of Japan and by AMED under Grant Number 19ek0109252h0003.
Competing interests None declared.
Patient consent for publication Not required.
Ethics approval Local Ethics Committee. The retrospective study design was approved by the ethics committee of Teikyo University (approval number: 10-042 and 19-157-2).
Provenance and peer review Not commissioned; externally peer reviewed.
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