Application of contact heat-evoked potentials in acute myelitis

Abstract

Objective To study the characteristics of the central part of the nociceptive system in acute myelitis (AM) with contact heat evoked potentials (CHEPs) and to document the potentials in patients with AM. Methods Twenty patients with AM were recruited in this study as an experimental group, and twenty healthy subjects were chosen as a control group. A heat foil was used to elicit pain and CHEPs. Thermal stimuli were applied at 54.5 ℃ at five sites: the dorsum of the hand, the proximal volar surface of the forearm, the skin of the leg 5 cm proximal to the medial malleolus, and at the C7 and T12 acupuncture locations. The latency and waveform of the evoked potentials were recorded. The conduction velocity of the A8 fibers of the peripheral nerves and of the spinal part of the spinothalamic tract were analyzed. The somatosensory evoked potential (SEP) and sensory conduction velocity (SCV) of the limbs were also examined, and the results were compared with the CHEP results. The results were compared between the two groups. Results The N 550 latencies of the CHEP on the dorsum of the hand, the inside of the leg, and at C7 and T12 were prolonged significantly in the patients with AM compared to the healthy controls. There were no significant differences in the nerve conduction velocity of the Aδ fibers and the velocity or amplitude of sensory nerve conduction in the limbs between the groups. The conduction velocities of the spinothalamic tract were significantly reduced in the patients with AM compared to the control group, while the peak latencies of N13 and the interpeak latencies of N9-N13 and N13-N20 in the AM patients were significantly prolonged compared to the healthy persons. In the patients with AM, CHEP abnormality in the lower limbs (17/20, 85%) was significantly higher than in the upper limbs, total CHEP abnormality and CHEP abnormality in the lower limbs were significantly greater than SEP abnormality. Conclusion Persons with AM have abnormalities in the central part of the nociceptive system. When used with MRI and other electrophysiological examinations, CHEP may contribute to diagnosing AM. It could be helpful in the differential diagnosis of AM from motor neuron diseases and peripheral nerve lesions. It is of great potential value in clinical practice. Key words: Heat-evoked potentials; Acute myelitis; Somatosensory evoked potentials