Association between Onodera’s prognostic nutritional Index and ultrasound-measured muscle thickness in amyotrophic lateral sclerosis: a retrospective cross-sectional study

Amyotrophic lateral sclerosis (ALS) causes progressive muscle wasting. Ultrasound-measured thickness captures this loss. Nutritional status influences ALS prognosis, yet the link between Onodera’s Prognostic Nutritional Index (OPNI) and muscle thickness is unclear. To assess whether OPNI correlates with thickness of the first dorsal interosseous (FDI), biceps brachii (BB) and masseter (MM) muscles, and to judge OPNI’s utility as a practical nutrition marker in ALS. In this retrospective study of 150 ALS patients, ultrasound quantified FDI, BB and MM thickness. Patients were stratified by OPNI quartile. Group differences were tested with ANOVA/Kruskal–Wallis. Multivariable generalized linear models, adjusting for age, sex, ALSFRS-R, King’s stage, comorbidities and lifestyle factors, examined independent associations; restricted cubic splines probed non-linearity. Muscle thickness rose progressively across OPNI quartiles (p p = 0.004), 0.022 cm thicker BB (95% CI 0.005–0.039; p = 0.011) and 0.011 cm thicker MM (95% CI 0.002–0.020; p = 0.013). Spline analysis supported a linear relationship. Higher OPNI independently predicts greater muscle thickness, indicating that better nutritional status parallels reduced muscle wasting in ALS. OPNI’s low cost and rapid availability support its use to flag patients for early nutritional intervention.