Split-hand and split-limb phenomena in amyotrophic lateral sclerosis: pathophysiology, electrophysiology and clinical manifestations

Abstract

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder affecting the upper and lower motor neurons. A key clinical feature of ALS is the absence of accurate, early-stage diagnostic indicators. ‘Split-hand syndrome’ was first described in ALS at the end of the last century and a considerable body of literature suggests that the split-hand phenomenon may be an important clinical feature of ALS. Considering the published investigations, it is conceivable that the ‘split-hand syndrome’ results from the associated upper and lower motor neuron degeneration, whose interaction remains to be fully clarified. Additionally, other split syndromes have been described in ALS involving upper or lower limbs, with a nuanced description of clinical and neurophysiological manifestations that may further aid ALS diagnosis. In this review, we endeavour to systematically present the spectrum of the ‘split syndromes’ in ALS from a clinical and neurophysiology perspective and discuss their diagnostic and pathogenic utility.

The senile hand: Age effects on intrinsic hand muscle CMAP amplitudes influence split‐hand index calculations

“…Wilbourn and Sweeney 1 described a pattern of dissociated wasting of hand muscles, consisting of pronounced atrophy of thenar muscles with relative sparing of the hypothenar eminence, a finding confirmed by others. 2,3 However, this pattern of muscular involvement has also been reported in other neuromuscular disorders, as well as in normal aging, 4 and it may be absent in some patients with amyotrophic lateral sclerosis (ALS). 3,5 A satisfactory explanation for this split hand phenomenon has not been forthcoming.…”

“…2,3 However, this pattern of muscular involvement has also been reported in other neuromuscular disorders, as well as in normal aging, 4 and it may be absent in some patients with amyotrophic lateral sclerosis (ALS). 3,5 A satisfactory explanation for this split hand phenomenon has not been forthcoming. 3,[6][7][8] A number of different methods have been used to detect the split hand phenomenon, based on the compound muscle action potential (CMAP) amplitude of small hand muscles (split-hand index, SHI), 3,5 F-wave frequency measurements, 9 and ultrasound measurement of muscle thickness 10 or their echo intensity.…”

“…3,5 A satisfactory explanation for this split hand phenomenon has not been forthcoming. 3,[6][7][8] A number of different methods have been used to detect the split hand phenomenon, based on the compound muscle action potential (CMAP) amplitude of small hand muscles (split-hand index, SHI), 3,5 F-wave frequency measurements, 9 and ultrasound measurement of muscle thickness 10 or their echo intensity. 11 Op de Coul 12 reported senile hand atrophy as a non-progressive, preferential atrophy of thenar muscles (senile abiotrophy), based on clinical observations.…”

The split-elbow index: A biomarker of the split elbow sign in ALS

“…The area under the curve 0.65 (considered a fair test), with optimal diagnostic cut off value of ≤0.62 exhibited a sensitivity of 72% and specificity of 62%. Importantly, the findings suggest that SEI is of limited diagnostic value when compared to other biomarkers of lower motor neurone loss in ALS ( Corcia et al, 2021 , Kalita et al, 2017 , Kim et al, 2016 , Kuwabara et al, 2008 , Menon et al, 2014a , Wang et al, 2020 ). Separately, the use of neurophysiological measures such as the motor unit number index (MUNIX), rather than CMAP amplitudes to calculate the split hand index, were shown to exhibit greater diagnostic utility in ALS ( Kim et al, 2016 ).…”

Possibilities of ultrasound in the diagnosis and differential diagnosis of amyotrophic lateral sclerosis: a literature review

“…Ультразвуковая верификация синдрома диссоциированной мышечной атрофии кисти при БАС. В результате многолетних наблюдений у пациентов с БАС были выявлены относительно специфические паттерны диссоциированной атрофии различных групп мышц [53,54]. Больше всего исследований посвящено симптому «расщепленной кисти», при котором атрофии больше подвержены короткая мышца, отводящая большой палец (m. abductor pollicis brevis), и первая тыльная межкостная мышца кисти (m. dorsal interossei) при относительной сохранности мышц гипотенара -мышцы, отводящей мизинец (m. abductor digiti minimi) [55,56].…”