Evoked potentials in a subject with a large-fibre sensory neuropathy below the neck

Abstract

The results from experiments in various modalities of evoked potentials are described in a subject with a complete large peripheral neuropathy below the neck. He has no tactile or position sensitivity below that level, but has retained fatigue, pain, and temperature sensation. Percutaneous electrical stimulation of peripheral nerves led to scalp recorded evoked potentials with thresholds and propagation velocities compatible with conduction along A-δ peripheral pathways. CO2 laser evoked potentials were similar to those seen in controls, further support for intact A-δ peripheral fibres. Movement-related cortical potentials (MRCPs) were recorded associated with active and passive movement of the middle finger. The former were normal, evidence that the termination of the MRCP is not dependent on peripheral feedback. By comparing passive MRCPs between controls and the subject it was possible to establish which parts of the potentials are visual and which are proprioceptive and to gain evidence of central reorganisation in the subject. Magnetic brain stimulation was used to show that the subject did not perceive induced movement, had a normal centrally originating silent period, and could focus his attention during real and imagined movement of the finger more successfully than could normal controls.Key words: sensory and motor evoked potentials, sensory neuropathy.