Theoretical discrimination index of postural instability in amyotrophic lateral sclerosis

To assess the usefulness of a theoretical postural instability discrimination index (PI_th) in amyotrophic lateral sclerosis (ALS). Prospective regression analyzes were performed to identify the biomechanical determinants of postural instability unrelated to lower limb motor deficits from gait initiation factors. PI_th was constructed using a logit function of biomechanical determinants. Discriminatory performance and performance differences were tested. Backward displacement of the pression center (APA_amplitude) and active vertical braking of the mass center (Braking-index) were the biomechanical determinants of postural instability. PI_th = - 0.13 × APA_amplitude - 0.12 × Braking-index + 5.67, (P < 0.0001, RSquare = 0.6119). OR (APA_amplitude) and OR (Braking-index) were 0.878 and 0.887, respectively, i.e., for a decrease of 10 mm in APA_amplitude or 10% in Braking-index, the postural instability risk was 11.391 or 11.274 times higher, respectively. PI_th had the highest discriminatory performance (AUC 0.953) with a decision threshold value [Formula: see text] 0.587, a sensitivity of 90.91%, and a specificity of 83.87%, significantly increasing the sensitivity by 11.11%. PI_th, as objective clinical integrator of gait initiation biomechanical processes significantly involved in dynamic postural control, was a reliable and performing discrimination index of postural instability with a significant increased sensitivity, and may be useful for a personalized approach to postural instability in ALS.