Peripheral and central somatosensory nerve conduction defects in Friedreich's ataxia.

Somatosensory evoked potentials were recorded over the clavicle, cervical spine, mastoid processes and the hand area of the contralateral somatosensory cortex to median nerve stimulation in 22 cases of Friedreich's ataxia. There was a marked attenuation of the clavicular potential, but little evidence of delay of this or the major cervical component. A dispersed and delayed cortical response was therefore suggestive of slowed conduction in central pathways. The cortical response was shown to be mediated by peripheral fibres with normal conduction velocity between stimulation sites at the wrist and the elbow.