Delayed Initiation of Supplemental Pain Management is Associated with Postherpetic Neuralgia: A Retrospective Study

Abstract

Background: Acute pain is a risk factor for developing postherpetic neuralgia (PHN), the most common complication of herpes zoster (HZ). Supplemental analgesics are frequently used in the treatment of acute herpetic pain. However, there are insufficient data regarding when to begin supplemental analgesics, and it is unknown whether the delayed use of supplemental analgesics increases the risk of PHN in high-risk patients. Objectives: This study aimed to evaluate the association between initial time of supplemental pain management and the risk of PHN in high-risk patients. Study Design: Retrospective study. Setting: The Department of Anesthesiology and Pain Medicine, Second Affiliated Hospital, Zhejiang University School of Medicine. Methods: We performed a retrospective study between May 13, 2017 and August 8, 2018 in our clinic. Multivariable logistic regression analysis was conducted to examine the independent factors associated with PHN. Supplemental pain management was defined as any use of opioids, tricyclic antidepressants, or nerve blocks. A subgroup analysis was conducted in patients who received supplemental pain management within the first 30 days of onset. According to the initial time of supplemental pain management, patients were divided into 2 groups: the early treatment group (≤ 14 days), and the late treatment group (> 14 days). The clinical outcomes in these 2 groups was compared for propensity score (PS) matching. Results: A total of 134 patients with HZ aged 50 years or older with moderate to severe pain were enrolled in this study. The delayed initiation of supplemental pain management (> 14 days) (odds ratio, 4.11; 95% confidence interval, 1.69-9.92; P = 0.002) and severity of rash (odds ratio, 2.93; 95% confidence interval, 1.22-7.01; P = 0.016) were independent factors associated with PHN. In the subgroup analysis, after PS matching, there were no significant differences in the baseline clinical parameters between the early and late treatment groups. The incidence of PHN was significantly lower in the early treatment group than the late treatment group (36. 4% vs. 72.7%; P = 0.015). Reduction in pain was also greater in the early treatment group. Limitations: The findings identified in the present study are specific to the patients who were relatively older and with moderate to severe pain. It is impossible to determine from our study whether younger individuals and individuals with mild acute pain will benefit from early supplemental treatments. Furthermore, because of the retrospective nature of the study, there may be some confounders that could not be controlled. Further prospective studies with larger sample sizes and longer follow-up periods are needed. Conclusions: The early use of supplemental pain management may decrease the risk of PHN. It might therefore be beneficial to consider administering supplemental pain management earlier in older patients with moderate to severe acute herpetic pain. Key words: Herpes zoster, postherpetic neuralgia, analgesia, opioid, nerve block, tricyclic antidepressant