Herpes zoster (HZ) is an infectious skin disease caused by the re-replication and activation of varicella-zostervirus (VZV) lurking in the sensory ganglia. Because VZV is neurotrophic, it has Patients with herpes are mostly accompanied by neuropathic pain. It is reported that 13.3%～42.2% of herpes zoster patients will have postherpetic neuralgia (PHN), which is manifested as persistent and intermittently aggravated neuropathic pain. Once PHN occurs, there is no clinically effective treatment method, most of the treatment effects are poor, and the patient suffers from pain for a long time. Studies have found that early nerve block therapy for HZ patients can effectively reduce the occurrence of PHN, so early prediction of the occurrence of PHN and treatment is of great significance. Current studies have found that the occurrence of PHN is related to the patient's age, location, skin lesion area, pain degree and course of disease. The visual analogue scoring method before treatment is reported. The higher the score, the higher the probability of PHN. However, the VAS score is more affected by the subjective factors of the patient, and the prediction bias based on the VAS score is larger, so it is necessary to explore more objective and accurate method of predicting PHN.

Infrared thermal imaging is an infrared light with a wavelength of 2 to 1 000 μm generated by a biological body, which is scanned by a special system and converted into an image signal after being processed by a photo-electric conversion and processing system. It has now developed into a more mature functional imaging technology, which can identify diseases, judge curative effects and prognosis through early analysis of the body's local thermal metabolism. It has the advantages of being relatively objective, non-invasive, non-radiative, non-polluting, simple and cheap. Infrared thermal imaging of healthy adults found that the symmetry of the body surface temperature was good, and the temperature difference was below 0.2℃. It is found that infrared thermal imaging can be used for early diagnosis of HZ; at the same time, it is also found that the acute phase lesion area of HZ is more likely to have PHN due to hyperthermia. There is no obvious correlation between the occurrence, but the selected cases have been treated with nerve block therapy to improve pain, which is different from the current drug treatment programs commonly used for HZ patients in my country. In order to further analyze the relationship between the infrared thermal imaging images before and after HZ acute drug treatment and PHN, and to find the infrared thermal imaging characteristics of PHN in the acute phase of HZ, this experiment was designed as a basis for further treatment of HZ patients. By analyzing the relationship between the patient's infrared thermography and VAS score at admission and discharge, and the occurrence of PHN in one month after discharge, the clinical value of the difference in infrared thermography before and after treatment in predicting PHN was evaluated.

Figure 1. Infrared thermography of patient with HZ occurring on the right side of T5-6 (A) The frontal infrared thermography at admission; (B) The back infrared thermography at admission; (C) The frontal infrared thermography at discharge; (D) The back infrared thermal thermography at discharge.

This experiment found that the temperature difference between the infrared thermal imaging examination and the corresponding temperature at discharge, and the VAS score at admission and discharge are related to the occurrence of PHN. Infrared thermal imaging of the patient when discharged from the hospital reflects the local metabolic state after treatment, which has a certain relationship with the final prognosis of the disease. The ΔT of patients in the non-PHN group decreases at the time of discharge. Under the threshold of predicting PHN, it indicates that during the hospitalization period. The patient's thermal metabolism quickly returns to normal, so the prognosis is good. The local metabolism of patients in the PHN group did not recover to the basic level during hospitalization, which means that the acute immune inflammatory inflammation in the diseased area has not fully recovered, so the final prognosis is poor. Therefore, the infrared thermal imaging state at the time of discharge can be used as a factor to predict PHN, and infrared thermal imaging is an objective indicator that reflects the local thermal metabolism state, and is not affected by subjective factors. Therefore, infrared thermal imaging has certain value for early prediction of the occurrence of PHN. The VAS score at discharge is lower than the predictive performance at admission. It may be related to the fact that the patient took analgesic drugs at the time of discharge to cover the patient's true pain at the time, which has a certain impact on the predicted outcome of PHN. The temperature difference between the affected side and the healthy side of the patient's infrared thermal imaging is an objective indicator and is not affected by subjective factors, while the VAS score is a subjective indicator that is affected by the patient’s mood and other aspects. Therefore, infrared thermal imaging is more effective in predicting PHN. The VAS scoring method is more clinically meaningful and objective, and is worthy of clinical promotion.