Correlation Between Electromyography and Severity and Prognosis of Upper Limb Herpes Zoster

There are differences in the clinical treatment schemes for patients with different severities of herpes zoster (HZ). Therefore, effective and accurate evaluation of disease severity is of great significance for the formulation of treatment plans. Postherpetic neuralgia (PHN) with long-term chronic pain leads to anxiety, depression, and even suicidal thoughts, which place a heavy burden on society and the family. Therefore, identifying risk factors and taking early intervention to reduce the occurrence of PHN is meaningful. Electromyography (EMG) can provide technical support for the early diagnosis of peripheral neuropathy. However, the application of EMG in HZ and PHN has rarely been reported. The purpose of this study was to compare the detection indices of EMG in patients with different severities and prognoses of HZ and to analyze the application of EMG in severity and prognosis of HZ.

This study aimed to explore the relationship between EMG and severity and prognosis of upper limb HZ.

A retrospective, observational study.

The study was carried out in the Pain Department of the affiliated Hospital of Jiaxing College in Jiaxing, China.

A total of 91 patients with upper limb HZ at the First Hospital of Jiaxing between January 2015 and August 2021 were enrolled. The patients were divided into mild, moderate, and severe HZ groups according to their numeric rating scale (NRS) scores. The occurrence of PHN was defined as a poor prognosis. The patients were divided into non-PHN and PHN groups according to the occurrence of PHN. Motor and sensory conduction indices of the median nerve were measured in each group. Spearman's correlation analysis was used to analyze the relationship between the EMG-related data of the median nerve and the NRS score and muscle strength. Univariate and multivariate logistic regression analyses were used to determine the independent influencing factors of PHN in patients with upper limb HZ, and the receiver operating characteristic (ROC) curve was drawn to evaluate the predictive value of EMG-related data in patients with upper limb HZ.

Among 91 patients, there were 29 patients in the mild HZ group, 31 in the moderate HZ group, and 31 in the severe HZ group. The sensory nerve action potential (SNAP) amplitude of the median nerve in the severe and moderate HZ groups was lower than that in the mild HZ group, and that in the severe HZ group was lower than that in the moderate HZ group (F = 22.192, P < 0.05). Through Spearman's correlation analysis, it was found that the compound muscle action potential (CMAP) and SNAP amplitudes of the median nerve on the affected limb were negatively correlated with the NRS score (r = -0.266, P = 0.011; r = -0.778, P < 0.001), and there was no significant correlation between each index and muscle strength (P > 0.05). Among 91 patients, 44 and 47 were in the non-PHN and PHN groups, respectively. Univariate and multivariate logistic regression analyses showed that the CMAP amplitude of the median nerve on the affected limb (OR = 0.241, 95% CI: 0.098-0.567, P = 0.001) and SNAP amplitude (OR = 0.268, 95% CI: 0.110-0.628, P = 0.002) were independent influencing factors of PHN. Through the analysis of the ROC curve, it was found that the CMAP and SNAP amplitudes of the median nerve on the affected limb had a high predictive value for PHN (AUC = 0.657, P = 0.010; AUC = 0.773, P < 0.001). The cutoff values were 5.45 mV and 10.80 mV, respectively; and the predictive value of the 2 indices combined was the highest (AUC = 0.785, P < 0.001).

The nonrandomized, single-center, small sample size, and retrospective design are major limitations of this study.

The CMAP and SNAP amplitudes of the median nerve on the affected limb were related to the degree of pain in patients with upper limb HZ. The CMAP and SNAP amplitudes of the median nerve on the affected limb can be used as prognostic factors for patients with upper limb HZ, and CMAP amplitude combined with SNAP amplitude is more valuable in predicting prognosis.