Nerve Ultrasound Detects Segmental Peripheral Nerve Variability in Friedreich Ataxia

<title>Abstract</title> <p> <bold>Introduction/Aims:</bold> Friedreich’s ataxia (FRDA) is the most common inherited ataxia and is caused by GAA repeat expansions in the <italic>FXN</italic> gene. With the emergence of disease-modifying therapy, structural biomarkers are increasingly needed. This study aimed to assess peripheral nerve cross-sectional area (CSA) in FRDA using high-resolution ultrasound to replicate and further characterize previously described ultrasonographic abnormalities. <bold>Methods:</bold> Ten FRDA patients underwent clinical evaluation with established scales (mFARS, FA-ADL, FARS-staging), nerve conduction studies, and standardized ultrasound of the median, ulnar, tibial, fibular, and sural nerves bilaterally. <bold>Results:</bold> Among 10 patients, ultrasound abnormalities were present in all (100%). Nerve enlargement was observed in every patient, occurring exclusively in the upper limbs (median and ulnar nerves), predominantly involving the median nerve at the upper arm (90%) and axilla (90%). Reduced CSA consistent with focal atrophy was identified in 50% of patients and was restricted to the upper limbs, most commonly at the forearm level of the median and ulnar nerves (20% each). Lower-limb nerves showed no significant CSA changes. Coexistence of enlargement and atrophy at different segments occurred in 50% of patients. <bold>Discussion:</bold> Peripheral nerve ultrasound detects segmental peripheral nerve size abnormalities in FRDA, characterized by the coexistence of focal enlargement and atrophy across different nerve segments. Further longitudinal studies are needed to clarify its potential role in disease characterization and monitoring. </p>