Utility of split hand index with different motor unit number estimation techniques in ALS

Utility of the split hand index (SI) in amyotrophic lateral sclerosis (ALS) has been reported when using the compound muscle action potential (CMAP) amplitude method (SI_{CMAP amp}). A motor unit number index (MUNIX) based SI method (SI_MUNIX) was purported to exhibit higher sensitivity. The present study assessed the clinical utility of SI, derived by CMAP amplitude, MUNIX and MScan-MUNE (SI_{MScanFit-MUNE}) methods, in ALS.

Sixty-two consecutive patients with neuromuscular symptoms (36 ALS and 26 ALS-mimics) were prospectively recruited. The SI was derived by dividing the product of the CMAP amplitude, MUNIX and MScan-MUNE values recorded over first dorsal interosseous and abductor pollicis brevis by values recorded over abductor digit minimi.

SI_{CMAP amp}, SI_MUNIX and SI_{MScanFit-MUNE} were significantly reduced in ALS, with SI_{CMAP amp} (area under curve (AUC) = 0.801) and SI_{MScanFit-MUNE} (AUC = 0.805) exhibiting greater diagnostic utility than SI_MUNIX (AUC = 0.713). SI_{CMAP amp} and SI_{MScanFit-MUNE} exhibited significant correlations with clinical measures of functional disability and weakness of intrinsic hand muscles.

SI differentiated ALS from mimic disorders, with SI_{CMAP amp} and SI_{MScanFit-MUNE} exhibiting greater utility.

The split hand index represents could serve as a potential diagnostic biomarker in ALS.