Unexpected nerve neuroimaging findings in Friedreich's ataxia

Friedreich’s ataxia (FRDA) is the most common autosomic recessive ataxia, caused by homozygous expansion of guanine–adenine–adenine (GAA) trinucleotide repeat in the frataxin gene leading to decreased expression of mitochondrial protein frataxin. The major neurological features are ataxia, dysarthria, areflexia, but sensory axonal neuropathy does also occur. Systemic symptoms (cardiomyopathy, scoliosis, diabetes mellitus) often coexist. Neurological phenotype is due to the involvement of dorsal root ganglia, sensory peripheral nerves, corticospinal tracts and dentate nuclei. Neurophysiological studies show severe reduction of sensory nerves action potential amplitude with preservation of nerve conduction velocities, consistent with sensory axonal damage. The neurophysiological abnormalities correlate with the size of GAA repeat expansion and with neuropathological findings (Santoro et al., 1999). Symptoms due to ataxia usually exceed those from sensory axonal neuropathy that are likely underestimated and contribute to patients’ disability. Nerve ultrasound (US) is an emerging technique that allows to visualize nerve size and echotexture (Goedee et al., 2013). In demyelinating neuropathies nerve enlargement – measured through cross-sectional area (CSA) – is common (Padua et al., 2014) while this is rarely found in axonal neuropathies (Goedee et al., 2013). We report on unexpected nerve neuroimaging findings in a FRDA patient.