Split hand index and ulnar to median ratio in Hirayama disease and amyotrophic lateral sclerosis

We report the relative usefulness of split hand index (SHI) and ulnar to median (UM) ratio in Hirayama disease (HD) and amyotrophic lateral sclerosis (ALS).

The patients with HD, ALS and matched controls were subjected to evaluation of UM ratio and SHI. Compound muscle action potentials (CMAPs) were recorded from abductor digit minimi (ADM) and first dorsal interosseous (FDI) by stimulating ulnar nerve at the wrist, and abductor pollicis brevis (APB) by stimulating median nerve at the wrist. UM ratio (ADM/APB) and SHI (APB × FDI/ADM) were calculated, and compared. Sensitivity and specificity of SHI and UM ratio in HD and ALS were calculated.

Twenty-six HD and 31 ALS patients were included. Twenty-six matched controls for HD and 20 for ALS were also evaluated. The APB amplitude was significantly lower in ALS compared to HD (6.89 ± 2.0 mv vs. 2.13 ± 1.27 mv, p = 0.01). UM ratio <0.86 had a sensitivity of 80.4% and specificity of 86.3% for HD. SH1 ≤ 5.2 had a sensitivity of 82% and specificity of 88.8% for ALS. UM ratio had a poor specificity for ALS (18.9%) and SHI for HD (34%).

UM ratio is more sensitive and specific for HD and SHI for ALS patients.