The Split-Hand Syndrome in Amyotrophic Lateral Sclerosis

The split-hand syndrome is a phenomenon seen in amyotrophic lateral sclerosis (ALS) in which muscle wasting affects the abductor pollicis brevis (APB) and first dorsal interosseous (FDI) muscles more than the abductor digiti minimi (ADM) muscle. These researchers asked whether the split-hand syndrome (named by the late Asa Wilbourn, MD) is specific to ALS. In this multicenter study, they prospectively analyzed compound muscle action potentials (CMAPs) in a consecutive series of 77 patients with ALS, in 171 healthy controls, and in 196 subjects with diverse non-ALS diseases affecting small hand muscles.

The CMAP amplitude ratios APB/ADM and FDI/ADM were reduced in 41% of patients with ALS but in only 5% of normal controls and 4% of non-ALS di…