C-Reactive Protein-to-Platelet Inflammatory Index (CPII) and Symptom Severity Score for Early Differentiation of Odontogenic Cervicofacial Necrotizing Fasciitis from Odontogenic Abscesses: A Retrospective Cohort Study

<b>Background/Objectives</b>: Early differentiation of odontogenic cervicofacial necrotizing fasciitis (NF) from odontogenic abscess (OA) is clinically challenging yet critical due to the need for urgent surgical and antimicrobial escalation. We evaluated whether a novel C-reactive protein-to-platelet inflammatory index (CPII = CRP/platelets), combined with a symptom-based Symptom Severity (SS) score, improves early discrimination of NF from OA. <b>Methods:</b> This retrospective cohort study included 234 hospitalized patients with cervicofacial odontogenic infections treated between January 2010 and December 2023 (25 NF, 209 OA). Admission clinical variables, SS and SIRS scores, and laboratory parameters were analyzed. CPII and established immunoinflammatory indices (including AISI, SII, NLR, PLR, and LMR) were calculated. Group comparisons were performed using nonparametric and categorical tests. Diagnostic performance was assessed by ROC analysis, and multivariable logistic regression evaluated independent associations with NF. <b>Results:</b> Compared with OA, NF patients were older (median 42 [IQR 35-59] vs. 35 [IQR 26-49] years; <i>p</i> = 0.0098) and more frequently had comorbidities (52% vs. 25.4%; OR 3.19; <i>p</i> = 0.0087). Trismus and dysphagia were more common in NF (84% vs. 60.8%, <i>p</i> = 0.0272; 88% vs. 53.6%, <i>p</i> = 0.0010), with higher SS and SIRS scores (both <i>p</i> < 0.0001). NF was associated with longer hospitalization (median 17 vs. 6 days; <i>p</i> < 0.0001) and more complications (40% vs. 5.7%; OR 10.94; <i>p</i> < 0.0001). CRP was markedly higher in NF (median 287 vs. 111.5 mg/L; <i>p</i> < 0.0001), platelets were lower (median 210 vs. 249 × 10⁹/L; <i>p</i> = 0.0091), and CPII was substantially higher (median 1.23 vs. 0.45; <i>p</i> < 0.0001). AISI did not differ between groups (<i>p</i> = 0.861). ROC analysis demonstrated excellent discrimination for SS score (AUC 0.9328, cut-off 12), CRP (AUC 0.9109, cut-off 221 mg/L), and CPII (AUC 0.9271, cut-off 0.75), whereas AISI showed limited discrimination (AUC 0.5108). In multivariable analysis, both SS score (adjusted OR 2.08 per 1 point) and CPII (adjusted OR 6.87 per 0.5 units) were independently associated with NF; the combined SS + CPII model achieved an AUC of 0.9726. <b>Conclusions:</b> CPII is a simple, admission-available biomarker that differentiates odontogenic cervicofacial NF from OA with excellent accuracy and provides strong complementary value when combined with SS score. AISI, despite prior utility for odontogenic abscess severity assessment, did not discriminate NF from OA in this cohort.