Objectives To investigate peripheral nerve ultrasound findings in patients with Friedreich’s ataxia (FRDA) and their relationship to the complex neuropathology of the somatosensory system in this condition.

Methods The ultrasound cross-sectional area of median and ulnar nerves at mid-forearm and mid-humerus level of eight non-diabetic FRDA patients (confirmed by GAA triplet expansion of the frataxin gene) were compared with eight age- and gender-matched healthy controls and with a reference population. All patients had sensory neuropathy with reduced or absent sensory action potentials on electrophysiological tests.

Results The mean cross-sectional area of the FRDA patient group was significantly larger than that of the healthy control group at all sites (p<0.05) with maximal differences at mid-humerus level. Seven of the eight FRDA patients had cross-sectional area measurements>2 SDs above our reference mean at one or more sites.

Conclusions The ultrasound finding of enlarged peripheral nerves in FRDA patients points to a structural abnormality at peripheral nerve level. This contrasts with the reduced cross-sectional area seen in the cerebellar ataxia, neuronopathy, vestibular areflexia syndrome (CANVAS) which is thought to be due to a pure sensory ganglionopathy (Pelosi et al, Muscle Nerve 2017, in press). While the specific pathophysiology in FRDA is unknown, nerve enlargement suggests, in agreement with recent neuropathological studies, that axonal loss from dorsal root ganglionopathy is not the sole mechanism underlying sensory neuropathy of FRDA. Myelin and/or stromal abnormality at peripheral nerve level may play a significant role.