Potential Associations Between CT-Derived Muscle Indices and Clinical Outcomes in Acute Pancreatitis

<i>Background and Objectives:</i> Acute pancreatitis (AP) is one of the most common gastrointestinal emergencies worldwide. Early identification of high-risk patients is essential to improve outcomes. Computed tomography (CT)-derived muscle mass indices, such as the psoas muscle index (PMI) and paravertebral muscle index (PvMI), have recently emerged as potential prognostic markers reflecting both nutritional and inflammatory status. This study aimed to investigate the relationship between CT-derived PMI and PvMI with disease severity, complications, and intensive care unit (ICU) requirement in patients with acute pancreatitis, and to evaluate their prognostic value across age- and sex-specific subgroups. <i>Materials and Methods:</i> This retrospective study included 179 patients hospitalized with AP between January 2023 and February 2025. The psoas muscle area (PMA) and paravertebral muscle area (PvMA) were measured at the L3 vertebral level on CT scans and normalized to height squared to calculate the PMI and PvMI levels. Additionally, patients were classified as having low or normal PMA and PvMA levels based on cutoff values from the existing literature. Clinical, biochemical, and outcome data-including disease severity, complications, and ICU requirement-were analyzed. Subgroup analyses were performed by sex and age (≥65 years). Logistic regression and ROC analyses were used to identify independent predictors and optimal cutoff values. <i>Results</i>: Overall, complications developed in 39.7% of patients, and ICU admission was required in 11.2%. The PMI levels were significantly correlated with albumin, hemoglobin, and inflammatory marker levels. In women, the PMI was independently associated with complicated AP (adjusted OR = 0.655, <i>p</i> = 0.018). In patients ≥65 years, the PvMI level was independently associated with ICU requirement (adjusted OR = 0.780, <i>p</i> = 0.047). The ROC analysis identified PMI ≤ 4.04 cm²/m² as the optimal cutoff for predicting complicated AP (AUC = 0.641, <i>p</i> = 0.049), and PvMI ≤ 18.88 cm²/m² for predicting ICU need (AUC = 0.684, <i>p</i> = 0.020), with moderate discrimination. <i>Conclusions</i>: CT-derived muscle indices might be associated with disease severity and adverse outcomes in AP, particularly among older (≥65 years) and female patients. PMI and PvMI may serve as practical prognostic markers to identify high-risk patients early, enabling timely nutritional and supportive interventions. Validation in larger prospective cohorts is warranted.