Application Of Contact Heat Evoked Potentials In Subacute Combined Degeneration Of The Spinal Cord

Subacute combined degeneration of the spinal cord (SCD)is the degeneration of nerve system,lacking of Vit B12,which mianly involvemengt the dorsal funiculus, lateral funiculus of the spinal cord and peripheral nerves.The clinical manifestation is varied,mainly exist the deep sensation deficiency,sensory ataxia,spastic paraplegia and peripheral neuropathy,and so on.Tegether with auxiliary examination to diagnose, such as serology,electrophysiology and MRI.Among these,neurologic electrophysiologic examination plays an important role in diagnosing SCD.To date,VEP,BAEP,MEP and SEP are available for testing visual, auditory, corticospinal pathways and the spinal cord dorsal column, but lack of corresponding electrophysiologic examination to test spinothalamic tract function. Contact heat evoked potentials is a new neurologic electrophysiologic examination, which can excite thin myelinated Ad fibers and unmyelinated C fibers, reflect the disorder of pain and warm pathway objectively.Objective:To study the characteristics of nociceptive system in subacute combined degeneration (SCD) by contact heat evoked potentials (CHEPs), and evaluate the CHEPs in the electrophysiological diagnosis of SCD.Methods:thirty-seven definite SCD patients and forty-six sex-, height-,and aged-matched healthy persons underwent stimulation of contact heat delivered via a circular thermode with a diameter of 27 mm(area of 573 mm2) to excite selectively nociceptors with a rapid rising time at 70℃/s to elicit pain and contact heat evoked potential(CHEP).Thermal stimuli were sent at 51℃intensity levels to four body sites:C7,volar surface of the forearm,the skin of leg 5 cm proximal to the medial malleolus and lumbar part. The CHEPs were recorded from Cz.The main components of the evoked potential were recorded.The conduction velocity (CV) of Ad fibers of peripheral nerves and N-wave latencies and N-P amplitudes of the central nerves were analyzed. The somatosensory evoked potential (SEP) and sensory conduction velocity (SCV) of the limbs were also evaluated. Sometimes, the hemoglobin(Hb), mean corpuscular volume(MCV),vitamin B12,folic acid of the subacute combined degeneration of the spinal cord(SCD) were also evaluated. Results:1. Comparison of four body sites with same intensity levels:there is no difference of VAS (P＜0.05)2 There is no significant correlation between age,hight and latency of N peak (P＞0.05);There is significant correlation between upper limb length and upper limb latency of N peak (P＜0.05);There is significant correlation between lower limb length and lower limb latency of N peak (P＜0.05).3 Comparison of four body sites with same intensity levels:CHEPs of lower limb are significantly prolonged compared with C7,upper limb and lumbar part (P＜0.05); CHEPs of the upper limb are no difference compared with lumbar part (P＞0.05); CHEPs of upper limb and lumbar part are significantly prolonged compared with C7 (P＜0.05), but there is no difference of N-P amplitude between them.4.The conduction velocity of Ad fibers of the upper and lower limbs is 22.873±14.359m/s vs 18.293±7.787m/s,respectively.5.VAS of SCD is significantly low compared with healthy subjucts (P＜0.05)6.CHEPs in patients are significantly delayed compared with healthy subjucts (P＜0.05).7.The conduction velocity of Ad fibers of SCD is lower than healthy subjucts (P＜0.05).8.CHEPs abnormalitiy is observed more often in the lower than the upper limb; CHEPs abnormalitiy of the lower / the upper limb is higher than SCV; CHEPs abnormalitiy of the lower limb is higher than SEPs;the lumber part in CHEP abnormalitiy is higher than MRI.9 The SCV abnormalitiy in the lower limb is higher than upper limb.10 There was linear correlation between the severity of lesions in CNS and level of VitB12 (P＜0.05); There was no linear correlation between the severity of lesions in CNS and level of falic acid (P＜0.05) Conclusions:1.The VAS of SCD is significantly low compared with healthy subjucts (P＜0.05), indicating there exist nociceptive system.2.N-wave latencies are difference between C7,the upper limb,lumbar part and the lower limb,C7 is first, the upper limb and lumbar part is second, the lower limb is third.3.The conduction velocity of the upper and lower limb is 22.873±14.359m/s VS 18.293±7.787m/s,respectively,this is Ad fibers.4.CHEPs abnormalitiy of SCD is higher than SEP,SCV,MRI, CEHPs can study the characteristics of nociceptive system in subacute combined degeneration (SCD) and detect subclinical lesions, thus contribute to the the diagnosis of SCD.5. There was linear correlation between the severity of lesions in CNS and level of VitB12, no linear correlation between the severity of lesions in CNS and level of falic acid,thus evaluate the severity of lesions in CNS through VitB12.6.There was linear correlation between the anemia and falic acid,no linear correlation between the anemia and VitB12,evaluate the anemia through the falic acid.