Neurological findings, neurophysiological examinations, and sural nerve biopsy in a case of Friedreich ataxia

We report on a 19-year-old Russian man with Friedreich ataxia with an expanded GAA repeat. The symptoms include ataxia of the trunk and lower extremities, dysdiadochokinesia of the upper extremities with left side dominance, square wave jerks, dysarthria, decreased muscle tone, areflexia, hypesthesia, decreased vibration sense and weakness in the lower extremities, extensor plantar response, skeletal abnormalies, and hypertrophic cardiomyopathy. Somatosensory Evoked Potentials elicited by median nerve stimulation suggested involvement of the central pathways, including the posterior column with lateral dominance. Sural nerve biopsy showed a marked decrease in large myelinated fibers (120/mm ²) and a moderate decrease in small myelinated fibers (1,430/mm ²) with normal density of unmyelinated fibers. Carbon dioxide laser stimulation of the upper limbs demonstrated "C-fiber component" toward Aδ fibers and a normal component toward C fibers. Immunohistochemical staining of a skin biopsy from the lateral malleolus for protein gene product 9.5 demonstrated a normal density (18/mm) of intraepidermal nerve fibers. To our knowledge, this is the first report using CO ₂ laser stimulation, skin biopsy, and sural nerve biopsy that unmyelinated fibers are not involved in Friedreich ataxia.