| Objective: Herpes zoster (HZ) or shingles is a common neurological disease, occurring in 90% of people over 50 years old. The most frequent complication of herpes zoster infection is post herpetic neuralgia (PHN), a kind of chronic neuropathic pain. 25% ~ 50% of patients over 50 years in age with PHN suffer from persistent pain. A number of geriatric patient's pain can persistent several months or years, influence people's sleep patterns, mood and general quality of life. This serious condition can also lead to anxiety and depression. PHN is easy to diagnose, however the mechanism of pathology remains unclear and there is a lack of effective treatment measures and methods to prevent PHN. Therefore research investigating the pain mechanism and pathophysiology of nerve injury caused by HZ and PHN has important clinic meaning to further early diagnosis and treatment of these conditions. It's known that thermal sensation is affected by neuropathic pain. Thermal quantitative sensory testing can be used to analyze and evaluate the degree of sensitivity of the sensory fibers and change of sensation and pain thresholds. TSA-II can measure the function of small nerve pathway sensation and pain signals quickly and exactly. The purpose of this study is to analyze the varying thresholds of Aδand C fibers for cold sensation, warm sensation, cold pain and heat pain, moreover to presume the mechanism of HZ and PHN in order to offer reference for effective treatment.Methods: Sixty patients were collected jointly from the department of pain medicine and rehabilitation and the outpatient department of the Deparment of Dermatology in the fourth Hospital of Hebei Medical University. The sample included 30 HZ (13 males and 17 females, mean age was 62.2±8.6) and 30 PHN (19 males and 11 females, mean age was 64.9±9.5). Thirty healthy persons including 12 males and 18 females with a mean age of 62.8±8.0 were also selected as a control group. The TSA-II thermal sensory analyzer was used to test the different sensory modalities in patients with Herpes Zoster and Postherpetic neuralgia, as well as in the control group subjects. The subjects were asked to point to the area experiencing pain and the indicated area was marked by the operator. Modified Marstock was chosen as the method of limits (including cold sensation, warm sensation, cold pain sensation and heat pain sensation) and a 30mm×30mm thermode was attached to the region where spontaneous pain was the most obvious around the affected dermatome on the trunk. An average of four readings of threshold temperature for cold and warm sensation was taken as a final result. An average of three readings of threshold temperature for cold and heat pain was taken as a final result. Subsequent measurements of different sensory modalities were taken in the same manner.Results: 1 Heat pain sensation of HZ (42.18±4.96℃) was signifi- cantly elevated when compared with heat pain sensation of control group (40.09±2.53)℃(P<0.05), and the mean difference is 2.09℃.Cold sensation, warm sensation and heat pain sensation of PHN [(22.75±4.89)℃, (38.84±4.44)℃, (44.77±4.13)℃] was significantly elevated when compared with corresponding threshold of control group [(28.76±1.18)℃, (34.65±0.88)℃, (40.09±2.53)℃] (P<0.05). The mean difference in threshold of cold sensation, warm sensation and heat pain sensation between PHN and control group were 6.01℃,4.20℃,4.69℃.2 The threshold of cold sensation, warm sensation and heat pain sensation of PHN was significantly elevated when compared with corresponding threshold of HZ (P<0.05). The difference in thresholds between HZ and PHN were found to be statistically significant (P<0.05), especially the difference of cold sensation [mean difference of cold sensation, warm sensation and heat pain sensation between HZ and PHN were 4.55℃,2.93℃,2.60℃].3 No significant correlation between cold sensation threshold and warm sensation threshold was found, while a negative correlation between cold sensation and warm sensation of PHN was observed (r=-0.59, P=0.001). Correlation between cold sensation and heat pain sensation, warm sensation and heat pain sensation of PHN were different from that of HZ [(r=-0.43, P=0.019), (r=-0.38, P=0.041); (r=0.59, P=0.001), (r=0.61, P< 0.0005)], but the difference between them was not found to be statistically significant in this study (P>0.05).Conclusion: 1 Aδ﹑C primary afferent nerves which conduct thermal sensation and pain sensation are injured and the function of those fibers is changed in the infected area in patients with HZ or PHN. The injured nerve in patients with HZ is mainly C fibers while in patients with PHN is mainly Aδfibers.2 The degree of injured Aδ﹑C primary afferent nerve is aggravated during the process of HZ developing to PHN, especially the injured Aδnerve which conducts cold sensation. The tolerances of cold sensation, warm sensation and heat pain in patients with PHN were higher than that in patients with HZ, while the ability to discriminate between thermal sensation and pain sensation was lower than that in patients with HZ. |
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