Split elbow sign: more evidence for the importance of cortical dysfunction in ALS

Dissociated muscle atrophy (DMA) is a well-recognised clinical phenomenon in amyotrophic lateral sclerosis (ALS).1 2 The best recognised of these phenomena is the split hand sign, clinically characterised by preferential wasting and weakness of the thenar group of intrinsic hand muscles (abductor pollicis brevis and first dorsal interosseous) compared to the hypothenar group.1 3 4 In addition, a split hand plus sign, characterised by preferential dysfunction of thenar muscles compared with the flexor pollicis longus has also been reported as a clinical feature of ALS.5 This dissociated pattern of muscle wasting has been attributed to greater cortical somatotopic representation of the intrinsic hand muscles, leading to larger corticomotoneuronal projections onto the vulnerable motor neurons with resultant propensity to …