This study was to investigate the clinical value of the systemic immune-inflammation index (SII) and prognostic nutritional index (PNI) in assessing the risk of developing postherpetic neuralgia (PHN) and to analyze the effects of inflammation and nutritional status on PHN.

Patients with herpes zoster were enrolled and divided into the PHN group and the non-PHN group. The clinical data and blood parameters of these patients were collected. The performance of SII and PNI alone and in combination in distinguishing between patients with and without PHN was investigated by ROC. Patients were stratified into three groups of high, medium, and low risk based on the cut-off values of SII and PNI. Kaplan–Meier curves and Cox risk regression were performed to analyze the association between PHN risk stratification and relevant factors.

The mean age of patients in the PHN group was significantly higher than that in the non-PHN group, and the proportion of hemorrhagic rash was higher. Neutrophil count and SII were significantly higher, whereas plasma albumin levels were significantly lower in the PHN group. The best predictive efficacy was achieved by SII and PNI in combination, and the incidence of PHN in the high-risk group was significantly higher than that in the low-risk group. Age, neutrophil count, and SII were independent risk factors for PHN, while plasma albumin and PNI were protective factors.

SII-PNI serves as an effective predictor of PHN risk, driven by hyperinflammation and nutritional status imbalance.