ABSTRACT
Objective To establish a method to evoke cerebral potentials by stimulating nociceptive fibers with contact heat evoked potential stimulator,evaluate the state of nociceptive system in patients with multiple sclerosis and assess the value of the potentials in multiple sclerosis(MS).Methods Thirty-six definite MS patients and 40 sex-,height-and aged-matched healthy persons underwent stimulation of contact heat delivered via a circular thermode to excite selectively nociceptors with a rapid rising time at 70℃/s to elicit pain and contact heat evoked potentiaI(CHEP).Thermal stimuli were sent at two intensity levels (47 ℃ and 51℃)to 3 body sites:volar surface of the forearm,the skin of leg 5 cm proximal to the medial malleolus and lumbar part.The CHEP were recorded from Cz.The relationship between the stimulus intensity and pain rating was observed,and the main components of the evoked potential were recorded.Then,somatosensory evoked potential(SEP)was examined in 36 patients with MS.Results CHEP were elicited reliably and stably in all control subjects.In contrast,in 4 patients there were no recordable CHEP on stimulation of the upper limb,and in some cases of lower limb(n=5).Conduction velocity of Aδ fihers was(18.1±7.3)m/s.The 21 MS cases had hypesthesia in upper limb and 29 cases in lower limb.The visual analog scale(VAS)for pain perception was higher in control subjects(upper limb:8.0±0.7;lower limb:7.9±0.7)than MS with hypesthesia(upper limb:6.1±0.9;lower limb:5.6±1.3,Z=-3.249 and -5.272,both P＜0.01).The group of patients (MS) with hypesthesia(upper limb 17 cases,lower limb 24 cases)had markedly reduced N-P amplitudes(upper limb:(30.5±12.8)μV;lower limb:(28.2±16.2)μV,t=-4.612 and -3.144,both P＜0.01)and prolonged N-wave latencies(upper limb:(387.3±34.2)ms;lower limb:(489.9±70.2)ms,t=4.790 and 4.798,both P＜0.01)compared with the control group in CHEP mediated by Aδ fibers.CHEP abnormality was observed more often in the lower(26/36,72.2%)than the upper limb(16/36,44.4%,P=0.031)and SEP(19/36,52.8%,χ~2=4.261,P=0.039).CHEP were abnormal in 3 of 15 skin areas with clinically normal nociception in upper limb,and in some cases of lower limb(2 of 7).Conclusions CHEP provides a clinically practical,non-invasive and objective measure,and can be a useful additional tool for the assessment of nocieptive system.Combined assessment of other Eps can help to document dissemination of demyelinating CNS lesions and detect subclinical lesions thus contribute to the diagnosis of multiple sclerosis.