Split-hand index: A diagnostic and prognostic marker in amyotrophic lateral sclerosis across varying regions of onset.

Abstract Objective The split-hand index (SI), a reliable diagnostic marker of amyotrophic lateral sclerosis (ALS), was prospectively assessed for differences across ALS subtypes and between the onset side of clinical symptoms or the dominant and contralateral sides. In addition, the prognostic utility of the SI was longitudinally assessed. Methods Two hundred and forty-five ALS patients underwent measurement of SI on both sides compared with 126 neuromuscular mimic disorders (NMD). A subset of patients (N = 45) underwent longitudinal assessment of SI. Results The SI was significantly reduced (SI RIGHT ALS 5.47(4.2), SINMD 9.0 (5.0); P  Conclusion The SI is reduced in all ALS subtypes most prominently in upper limb onset disease, on the side of clinical onset, and in patients with Awaji definite/probable diagnostic category. Significance The split-hand index is a reliable diagnostic and outcome biomarker across ALS subtypes and may have potential utility in a clinical trial setting, although further multicenter studies are required to confirm this.