Split hand phenomenon: An early marker for amyotrophic lateral sclerosis

Background: Amyotrophic lateral sclerosis (ALS) is a progressive disease characterized by degeneration of upper and lower motor neurons. Time from symptom onset to confirmed diagnosis has been reported from 8 to 15 months in ALS. Objectives: To describe the frequency of the split hand phenomenon and propose it as an early biomarker for ALS diagnosis. Methods: A retrospective, analytical, descriptive, and single-center observational study was performed. The split hand ratio was determined by dividing distal abductor pollicis brevis/abductor digit minimi compound muscle action potentials; a result < 0.6 was considered present. Results: Fifty-four patients with ALS diagnosis were included in the study. The split hand ratio was identified in 61.5% of patients with definite ALS, in 68.7% with probable ALS, 80% with possible ALS, and in 50% with suspected ALS. The split hand phenomenon was identified in 60% of patients within 12 months of symptom onset. Conclusion: We provide evidence for an additional neurophysiological tool that helps early diagnosis of ALS.