Electrophysiology and nerve biopsy: comparative study in Friedreich's ataxia and Friedreich's ataxia phenotype with vitamin E deficiency.

The authors report a comparative study of peripheral nerve conductions and nerve biopsy and somatosensory evoked potentials between 15 patients with Friedreich's ataxia and 15 patients with Friedreich's ataxia phenotype with selective vitamin E deficiency. The patients in the two groups are of similar age, age of onset, and clinical phenotype. Peripheral motor nerve action potential amplitude, and conduction velocities are within normal ranges in the two groups. In the Friedreich's ataxia group there is an early and severe peripheral sensory axonal neuronopathy, characterised by an important reduction of the amplitude of sensory action potential, and important loss of myelinated fibres with complete disappearance of large myelinated fibres without any regenerative process. In the Friedreich's ataxia phenotype with selective vitamin E deficiency group there is slight-to-moderate axonal sensory neuropathy with normal to moderate decrease of large myelinated fibre density and important regeneration in nerve biopsy. Somatosensory evoked potentials are markedly involved in the two groups asserting a severe involvement of somatosensory pathway in lumbar, thoracic and cervical spinal cord. These findings suggest that the pathological mechanism involved in the two diseases are different: central peripheral axonopathy in Friedreich's ataxia and central distal axonopathy in Friedreich's ataxia phenotype with selective vitamin E deficiency.