Disproportionate muscle atrophy is a distinct phenomenon in amyotrophic lateral sclerosis (ALS); however, preferentially affected leg muscles remain unknown. We aimed to identify this split-leg phenomenon in ALS and determine its pathophysiology. Patients with ALS (n = 143), progressive muscular atrophy (PMA, n = 36), and age-matched healthy controls (HC, n = 53) were retrospectively identified from our motor neuron disease registry. We analyzed their disease duration, onset region, ALS Functional Rating Scale-Revised Scores, and results of neurological examination. Compound muscle action potential (CMAP) of the extensor digitorum brevis (EDB), abductor hallucis (AH), and tibialis anterior (TA) were reviewed. Defined by CMAP_EDB/CMAP_AH (SI_EDB) and CMAP_TA/CMAP_AH (SI_TA), respectively, the values of split-leg indices (SI) were compared between these groups. SI_EDB was significantly reduced in ALS (p < 0.0001) and PMA (p < 0.0001) compared to the healthy controls (HCs). SI_TA reduction was more prominent in PMA (p < 0.05 vs. ALS, p < 0.01 vs. HC), but was not significant in ALS compared to the HCs. SI was found to be significantly decreased with clinical lower motor neuron signs (SI_EDB), while was rather increased with clinical upper motor neuron signs (SI_TA). Compared to the AH, TA and EDB are more severely affected in ALS and PMA patients. Our findings help to elucidate the pathophysiology of split-leg phenomenon.

不成比例的肌肉萎缩是肌萎缩侧索硬化症 (ALS) 的一个明显现象；然而，优先受累的腿部肌肉仍然未知。我们旨在确定 ALS 中的这种分腿现象并确定其病理生理学。从我们的运动神经元疾病登记处回顾性地确定了患有 ALS（n = 143）、进行性肌肉萎缩（PMA，n = 36）和年龄匹配的健康对照（HC，n = 53）的患者。我们分析了他们的病程、发病区域、ALS 功能评定量表修订分数和神经系统检查结果。回顾了趾短伸肌 (EDB)、拇外展肌 (AH) 和胫前肌 (TA) 的复合肌肉动作电位 (CMAP)。由 CMAP _EDB / CMAP _AH (SI _EDB ) 和 CMAP 定义_TA / CMAP _AH (SI _TA )，分别比较了这些组的分腿指数(SI)的值。与健康对照 (HC) 相比，ALS (p <0.0001) 和 PMA (p <0.0001) 中的SI _EDB显着降低。SI _TA减少在 PMA 中更为显着（与 ALS 相比 p <0.05，与 HC 相比 p <0.01），但与 HC 相比，ALS 中的SI _TA减少不显着。SI 被发现随着临床下运动神经元体征 (SI _EDB )显着降低，而随着临床上运动神经元体征 (SI _TA )而增加。与 AH 相比，TA 和 EDB 在 ALS 和 PMA 患者中受到的影响更严重。我们的发现有助于阐明分腿现象的病理生理学。