Quantitative MRI Analysis of Brachial Plexus and Limb‐Girdle Muscles in Upper Extremity Onset Amyotrophic Lateral Sclerosis

Background Recent evidence highlights the potential of axonal degeneration as a biomarker for amyotrophic lateral sclerosis (ALS) detection. However, the diagnostic potential of peripheral nerve axon changes in ALS remains unclear. Purpose To evaluate the diagnostic performance of quantitative MRI of the brachial plexus and limb‐girdle muscles (LGMs) in patients with upper extremity onset of ALS. Study Type Retrospective. Population 47 patients with upper extremity onset of ALS and 20 healthy volunteers. Field Strength/Sequence 3‐T, three‐dimensional sampling perfection with application‐optimized contrasts using different flip angle evolutions with short‐tau inversion recovery sequences, T2‐weighted turbo spin‐echo Dixon sequence. Assessment The cross‐sectional area (CSA) and nerve‐muscle T2 signal intensity ratio (nT2) of the bilateral brachial plexus as well as the CSA and fat fraction (FF) of the bilateral LGMs were assessed by two radiologists. Disease severity and clinical stage of ALS patients were assessed by two neurologists. Statistical Tests Student's t ‐test, Wilcoxon rank‐sum test, binary logistic regression, interclass correlation coefficient, receiver operating characteristic analysis, and correlation analysis were performed for MRI quantitative metrics and clinical variables. Significance level: P < 0.05. Results In the affected limbs of patients with ALS, the CSA of the brachial plexus roots, trunks, and cords and the nT2 values of the brachial plexus trunks were significantly smaller than in the healthy controls. In the LGMs, the affected limbs of ALS showed significantly smaller CSA and higher FF than controls. The model containing parameters such as brachial plexus trunk CSA, subscapularis CSA, infraspinatus CSA, and subscapularis FF had excellent diagnostic efficacy for ALS. Additionally, increased subscapularis FF and supraspinatus FF were correlated with disease severity, and subscapularis CSA was negatively correlated with the clinical stage. Data Conclusion Brachial plexus thinning, LGM atrophy, and fatty infiltration might serve as MRI‐derived biomarkers for ALS with upper extremity onset. Level of Evidence 4 Technical Efficacy Stage 2