Somatosensory evoked response in controlled A-alpha sensory fiber disease.

In contrast to the distal sensory response, the somatosensory evoked response (SSER) is detectable in patients with A-alpha sensory fiber diseases such as Friedreich's ataxia. In four patients with this disease a combined histological and electro-physiological investigation of sensory propagation was performed. The sural nerve was analyzed in terms of the various fiber diameters and the distal sensory and somatosensory evoked cortical responses recorded after sural and median nerve (finger) stimulation. A distinct evoked response could be detected with rather low amplitudes and retarded latency times, while in general no distal sensory response was found. The anatomical physiological consequences are discussed.