Early inflammatory response is associated with antibiotic treatment outcomes in acute phlegmonous appendicitis: a retrospective cohort study

Abstract

Acute phlegmonous appendicitis is considered an intermediate inflammatory subtype between uncomplicated and complicated appendicitis. Although nonoperative management is increasingly accepted for uncomplicated appendicitis, evidence for phlegmonous appendicitis remains limited. This study aimed to evaluate the 1-year success rate of antibiotic treatment and identify early factors associated with treatment outcomes. This retrospective study included 476 patients with CT-defined acute phlegmonous appendicitis treated at Zhongshan Hospital between January 2021 and June 2025. Patients with incomplete follow-up were excluded from the primary analysis. Of these patients, 374 initially received antibiotic therapy, and the primary endpoint was the 1-year success rate of antibiotic treatment. Clinical characteristics, appendicolith status, and changes in inflammatory markers during the first 24 h were analyzed. Multivariable logistic regression was performed to identify factors associated with successful antibiotic treatment, and a nomogram was developed and internally validated. The model was considered exploratory and requires external validation before clinical application. The complete-case 1-year treatment success rate among the 374 patients receiving antibiotic therapy was 50.3% (188/374; 95% CI 45.2–55.3%). Patients with appendicoliths had a significantly lower success rate than those without appendicoliths (31.3%; 95% CI 21.5–43.2% vs. 54.4%; 95% CI 48.8–59.9%, P < 0.001). Baseline clinical characteristics showed limited association with treatment outcomes, whereas early inflammatory marker changes were more closely associated with outcomes. Multivariable analysis demonstrated that a WBC count decrease ≥ 20% (OR 1.92, 95% CI 1.08–3.42, P = 0.027) and a neutrophil percentage (N%) decrease ≥ 6% (OR 3.65, 95% CI 2.08–6.39, P < 0.001) within the first 24 h were independently associated with higher odds of successful antibiotic treatment. In contrast, the presence of appendicolith was independently associated with lower odds of successful antibiotic treatment (OR 0.46, 95% CI 0.25–0.85, P = 0.013). A nomogram incorporating these three variables demonstrated moderate discrimination (AUC = 0.738). Approximately half of patients with acute phlegmonous appendicitis achieved successful treatment with antibiotics. Early reductions in inflammatory markers were associated with treatment outcomes and may provide information for early risk stratification. A nomogram incorporating appendicolith status and early inflammatory marker changes may estimate the likelihood of treatment success; however, this model was considered exploratory and requires external validation.