Abstract
Community-acquired pneumonia (CAP) is a leading cause of morbidity and mortality in older adults, with risk stratification relying on clinical scoring systems that often overlook sarcopenia - a critical prognostic factor in geriatric populations. The pectoralis muscle index (PMI), derived from chest CT, has emerged as an objective marker of muscle mass but its integration with established prognostic tools remains underexplored. This study evaluated whether incorporating PMI enhances the predictive performance of systolic blood pressure, oxygenation, age, and respiratory rate (SOAR), systemic immune-inflammation index (SII), and prognostic nutritional index (PNI) scores for 30-day mortality in elderly CAP patients. In this retrospective single-center study, 389 hospitalized CAP patients (≥65 years) with admission CT scans were analyzed. PMI was calculated at the T4 vertebral level. Predictive performance was assessed via Receiver Operating Characteristic (ROC) analysis comparing standalone scores (SOAR, SII, PNI) versus PMI-integrated models. The 30-day mortality rate was 21.1%. PMI alone showed strong discrimination (AUC = 0.84), comparable to SOAR (AUC = 0.86). The PMI + SOAR combination achieved superior predictive accuracy (AUC = 0.92, P < .001 vs SOAR alone), with sex-specific PMI cutoffs of 7.88 cm²/m² (women) and 8.39 cm²/m² (men). PMI also improved PNI (AUC = 0.88 vs 0.76) but had limited synergy with SII. PMI is an independent predictor of 30-day mortality in geriatric CAP. Its integration with SOAR significantly enhances risk stratification, underscoring the clinical value of assessing muscle mass alongside conventional respiratory parameters.