Time to Epidural Steroid Injection and Complete Remission in Zoster-Associated Pain: A Multicenter Retrospective Cohort Study

Background: In zoster-associated pain (ZAP), earlier epidural steroid injection (ESI) has been associated with better outcomes, but optimal timing remains unclear, and prior studies have largely relied on pain reduction alone. Methods: In this multicenter retrospective cohort, 215 patients with ZAP who completed a three-session ESI course were classified into early (<30 days) and delayed (≥30–≤180 days) groups. The primary endpoint was complete remission at 12 weeks (≥50% visual analog scale [VAS] reduction, VAS ≤ 2, and sensory normalization); successful response (≥50% VAS reduction) served as the secondary endpoint. An ordered three-category framework and an exploratory generalized Youden index threshold analysis were applied. Results: Complete remission occurred in 82.1% versus 39.0% and successful response in 91.7% versus 67.8%. Each additional day of delay was associated with lower odds of complete remission (adjusted odds ratio [aOR], 0.957; p < 0.001) and higher odds of a worse outcome category (aOR, 1.030; p < 0.001). Exploratory candidate boundaries were 22 and 42 days. Conclusions: Earlier ESI initiation was associated with a higher likelihood of complete remission incorporating pain reduction, low residual pain intensity, and sensory normalization. These findings highlight the clinical relevance of treatment timing and recovery assessment beyond pain reduction alone in ZAP.