Utility of Dissociated Intrinsic Hand Muscle Atrophy in the Diagnosis of Amyotrophic Lateral Sclerosis

Abstract

The split hand phenomenon refers to predominant wasting of thenar muscles and is an early and specific feature of amyotrophic lateral sclerosis (ALS). A novel split hand index (SI) was developed to quantify the split hand phenomenon, and its diagnostic utility was assessed in ALS patients. The split hand index was derived by dividing the product of the compound muscle action potential (CMAP) amplitude recorded over the abductor pollicis brevis and first dorsal interosseous muscles by the CMAP amplitude recorded over the abductor digiti minimi muscle. In order to assess the diagnostic utility of the split hand index, ALS patients were prospectively assessed and their results were compared to neuromuscular disorder patients. The split hand index was significantly reduced in ALS when compared to neuromuscular disorder patients (P<0.0001). Limb-onset ALS patients exhibited the greatest reduction in the split hand index, and a value of 5.2 or less reliably differentiated ALS from other neuromuscular disorders. Consequently, the split hand index appears to be a novel diagnostic biomarker for ALS, perhaps facilitating an earlier diagnosis.

Neurophysiological Differences between Flail Arm Syndrome and Amyotrophic Lateral Sclerosis

“…Split-hand phenomenon is one important clinical feature of ALS patients, characterized by preferential wasting of the thenar muscles, while the hypothenar muscles are relatively less involved[ 21 – 23 ]. Our findings showing significantly increased SI in ALS, are consistent with previous studies, and suggest that split-hand is an important neurophysiological feature of ALS[ 22 , 24 – 26 ]. Since these muscles of thenar and hypothenar were innervated by the same myotomes, the difference of involvement severity of these two sites seems not be derived from spinal cord.…”

Tracking motor neuron loss in a set of six muscles in amyotrophic lateral sclerosis using the Motor Unit Number Index (MUNIX): a 15-month longitudinal multicentre trial

“…The recently suggested electrophysiological ‘split-hand-index’, which uses the CMAP amplitude for calculation, might also be adapted for MUNIX measurements 24 25 27 28. This index additionally uses the first interosseus dorsalis muscle (FDI) 27 28. MUNIX measurements from the FDI have already been performed 18.…”

Dissociated lower limb muscle involvement in amyotrophic lateral sclerosis and its differential diagnosis value

“…Wilbourn 4 first reported split hand syndrome in upper limb-onset ALS patients, which refer to Abductor pollicis brevis (APB) and first dorsal interosseous (FDI) muscles being predominantly affected by relative sparing of abductor digiti minimi (ADM). Menon P and Park D 5 further confirmed this phenomena through electrophysiology studies. They revealed that compound muscle action potentials (CMAP) of APB and FDI were significantly lower than CMAP of ADM.…”

“…They revealed that compound muscle action potentials (CMAP) of APB and FDI were significantly lower than CMAP of ADM. The results were presented as split hand index (SI, ) 5,6 .They found that the “split hand” could be used to differentiate ALS from CSA 5,7 . Recently, Neil reported dissociated lower limb muscle involvement in ALS 8 .…”