Split-hand sign in the patients with amyotrophic lateral sclerosis

Abstract

Objective To investigate the diagnostic value of the split-hand sign in amyotrophic lateral sclerosis (ALS). Methods Ninety ALS patients, 41 patients with other neuromuscular disorders and 71 normal controls were recruited for conventional nerve conduction study. Compound muscle action potential (CMAP) amplitude recorded from abductor pollicis brevis (APB), abductor digiti minimi (ADM) and first dorsal interosseous (FDI), CMAP amplitude ratios, CMAP amplitude differences and split-hand index (SI) were analyzed. Results The APB/ADM CMAP amplitude ratio was significantly lower in the ALS patients (0.44(0.44)) than that in the patients with other neuromuscular disorders (1.31(0.87); z=6.967, P<0.01) and the normal controls (0.99(0.42); z=7.687, P<0.01). The FDI/ADM CMAP amplitude ratio was significantly decreased in the ALS patients (0.79(0.46)) compared with that in the normal controls (1.23(0.39); z=5.899, P<0.01). The FDI/ADM CMAP amplitude ratio was comparable between the ALS patients and the patients with other neuromuscular disorders (0.93(0.62); z=1.737, P=0.081). SI was significantly lower in the ALS patients (2.42(3.14)) than that in the patients with other neuromuscular disorders (10.10(6.54); q=7.947, P<0.05) and the normal controls (17.93(8.32); q=10.827, P<0.05). SI <5.2 can help differentiate ALS from mimic disorders, with a sensitivity of 83.33% and specificity of 96.43%. Conclusions The split-hand sign appears to be a specific feature of ALS. SI robustly differentiates ALS from mimic disorders and potentially facilitates an earlier diagnosis of ALS. Key words: Amyotrophic lateral sclerosis; Split-hand sign; Split-hand index; Nerve conduction study