Quantitative Ultrasonographic Assessment of Muscle Structure and Correlations with Motor Function Scales in Nusinersen-Treated Children with Spinal Muscular Atrophy.

Abstract

To investigate ultrasonographic muscle thickness and echointensity in children with spinal muscular atrophy (SMA) receiving nusinersen therapy by comparing these parameters with healthy controls and determining their relationship with motor function scale scores. Cross-sectional case-control study SETTING: Tertiary university hospital. Thirty-four children with SMA (Types 1-3) receiving disease-modifying therapy with nusinersen and 34 age- and sex-matched healthy controls. N/A. Muscle thickness of the biceps brachii/brachialis (BB/B), forearm flexors (FF), quadriceps femoris (QF), and tibialis anterior (TA) was measured using B-mode ultrasonography. Muscle echointensity was quantified using grayscale analysis in ImageJ software. Motor function was assessed using the Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP-INTEND), the Hammersmith Functional Motor Scale-Expanded (HFMSE), and the Revised Upper Limb Module (RULM). Children with SMA demonstrated significantly reduced muscle thickness and increased echointensity across all examined muscles compared with controls (p < 0.05). TA echointensity showed strong negative correlations with CHOP-INTEND and HFMSE scores (r = -0.781 and r = -0.585, respectively; p < 0.001). In addition, moderate positive correlations were observed between RULM scores and the thickness of the BB/B and FF muscles (r = 0.412 and r = 0.425, respectively; p < 0.05). Ultrasonography enables objective evaluation of muscle structure in children with SMA receiving disease-modifying therapy, with muscle thickness and echointensity demonstrating significant associations with motor function. Tibialis anterior echointensity may represent a promising biomarker for disease monitoring.