Split-hand index in amyotrophic lateral sclerosis: an F-wave study

Objective: Split-hand sign is a useful clinical and electrophysiological feature in the diagnosis of amyotrophic lateral sclerosis (ALS). We proposed a novel split-hand index (SI) using F-wave persistence (FP) and assessed its diagnostic utility in ALS. Methods: Eighty-three consecutive ALS patients were recruited, and 50 healthy, age-, and height-matched volunteers were used as a control group. Compound muscle action potentials (CMAP) and FP were recorded from the abductor pollicis brevis (APB), first dorsal interosseous (FDI), and the abductor digiti minimi (ADM) muscles. The SI derived from FP was calculated using the following formula: SIFP = (FPAPB ×FPFDI)/FPADM. The sensitivity and specificity of SIFP and SICMAP in differentiating ALS from healthy controls (HCs) were derived from receiver-operating characteristic (ROC) curve analysis. Results: Both SIFP and SICMAP were significantly reduced in ALS patients. The ROC curve analysis indicated that both SIFP and SICMAP reliably differentiated ALS from HCs [0.92 (95% CI: 0.88-0.95); 0.86 (95% CI: 0.82-0.91)], but SIFP showed better diagnostic accuracy than SICMAP (p = 0.04), with a high sensitivity (81.2%) and specificity (97%). In subgroup analyses, SIFP appeared to be a better variable than SICMAP for differentiation of ALS patients with normal CMAP from HCs, with an area under the curve of 0.87 (95% CI: 0.80-0.93), sensitivity of 69.4%, and specificity of 94%. Conclusion: The SIFP reliably distinguished ALS patients from HCs and may be more sensitive for determining the split-hand pattern of ALS than SICMAP, particularly in the early stage of the disease.