Clinical and Somatosensory Correlates of Persistent Zoster-Associated Pain at One Month: A Prospective Multicenter Cohort Study

Background/Objectives: Persistent pain after acute herpes zoster (HZ) carries substantial functional burden, but early markers of pain persistence remain uncertain. In an exploratory analysis, we examined whether baseline clinical features and a simple affected-to-contralateral pressure-pain threshold (PPT) ratio were associated with persistent zoster-associated pain approximately one month after rash onset. Methods: In this prospective multicenter observational cohort, 117 adults with acute HZ (mean age 58.7 ± 14.7 years, 60.7% women, 18.8% with diabetes mellitus, 16.2% immunosuppressed, 58.1% thoracic dermatome) were assessed 1–7 days after rash onset with clinical variables, the Douleur Neuropathique 4 (DN4) questionnaire, bedside sensory examination and standardized pressure algometry. Two equally reported outcome definitions were applied at follow-up: average and worst 24 h numerical rating scale (NRS) pain ≥ 3. Firth penalized logistic regression was used, with bootstrap internal validation that repeated the predictor-selection step within each resample. Results: Of 117 participants, 109 (93.2%) completed follow-up at a mean of 29.8 ± 3.3 days. Average 24 h NRS ≥ 3 occurred in 25/109 (22.9%) and worst 24 h NRS ≥ 3 in 42/109 (38.5%). Under the average-pain definition, age per 10 years (odds ratio [OR] 1.60, 95% confidence interval [CI] 1.03–2.59), baseline NRS per point (OR 1.43, 1.11–2.06) and PPT ratio per 0.1 increase (OR 0.69, 0.50–0.92) were associated with the outcome; under the worst-pain definition only baseline NRS remained associated (OR 1.18, 1.02–1.39), with attenuation of both age (OR 1.34, 0.98–1.86) and PPT ratio (OR 0.86, 0.68–1.08). Apparent areas under the receiver operating characteristic curve (AUCs) were 0.863 and 0.740, respectively; the optimism-corrected AUC for the average-pain model was 0.831. The PPT ratio was strongly correlated with bedside allodynia (Spearman ρ = −0.82). Conclusions: PPT asymmetry was associated with one-month pain persistence under one of two outcome definitions but overlapped substantially with clinically assessed allodynia. These exploratory associations require prespecified confirmation before any clinical application.