[A neurophysiological study of the alterations to the central and peripheral nervous systems in Friedreich's ataxia]

Friedreich's ataxia (FA) is the most common type of early-onset hereditary ataxia, starting during childhood and adolescence. Both the central and peripheral nervous systems are compromised. AIM. To describe the alterations found in the neurophysiological examination and their relation with the degree of disability and the time the disease lasts.

We examined 26 patients diagnosed with FA by means of a genetic study with multimode evoked potentials, transcranial magnetic stimulation, peripheral nerve conductions and a study of small myelinated-unmyelinated sensory fibres using quantitative sensory tests (thermotest).

Peripheral sensory potentials, somatosensory potentials and motor responses with transcranial stimulus were pathological in all patients. From the early stages of the disease there were both peripheral sensory neuropathy and alterations of the somatosensory potentials and motor responses with transcranial stimulus in the lower limbs. Alterations in the somatosensory potentials in the upper limbs and the motor responses obtained by transcranial stimulus were related with the degree of disability. Brainstem and visual potentials were altered in 16 and 28% of cases, respectively; only reduced amplitude of the P100 was related with the degree of disability. In the thermotest, 50% of the patients showed alterations.

Increased disability in patients with FA is related with the progressive involvement of the somatosensory and pyramidal pathways. Although traditionally reports have claimed that the thick myelinated fibres are the ones involved in FA, we found alterations in the small calibre fibres in half the patients.