Assessing disease activity in polymyalgia rheumatica using the systemic immune-inflammation index: A retrospective...

Polymyalgia rheumatica (PMR) is an inflammatory rheumatic condition predominantly affecting older individuals, characterized by pain and stiffness in the shoulder and pelvic girdles. The PMR Activity Score (PMR-AS) is a composite tool for assessing disease activity, yet easily accessible inflammatory biomarkers that correlate with disease activity remain limited. The Systemic Immune-Inflammation Index (SII), derived from peripheral blood counts has emerged as a novel marker reflecting systemic inflammation.

To investigate the relationship between the SII index and disease activity as measured by the PMR-AS in patients diagnosed with PMR.

In this retrospective cross-sectional study, 180 patients diagnosed with PMR were included. Clinical and laboratory data at diagnosis were analyzed. PMR-AS was calculated at baseline. Pretreatment complete blood counts were used to determine the SII index. The association between SII index and PMR-AS was evaluated using Pearson correlation analysis. Patients were stratified into low disease activity and moderate-high disease activity groups based on a PMR-AS cut-off of 7. Multivariate linear regression was conducted to evaluate the independent association between SII index and PMR-AS.

Among 180 patients with PMR, 86 (47.8%) had moderate-high disease activity. Coronary artery disease (CAD) was significantly more common in this group. Patients with moderate-high disease activity showed elevated WBC and neutrophil counts, reduced lymphocyte counts, and higher CRP levels. The SII index was markedly higher in the moderate-high disease activity group and demonstrated a moderate correlation with PMR-AS (r = 0.47). In multivariate analysis, CAD and SII index were independent predictors of moderate-high disease activity. ROC analysis confirmed that SII index demonstrated acceptable discriminatory performance moderate-high disease activity.

The SII index may reflect disease activity in PMR and could be considered a non-invasive, cost-effective adjunct to clinical evaluation. Key Points • The SII index is a powerful predictor of disease activity in PMR. • Presence of CAD and higher SII index were independently associated with moderate-high disease activity, highlighting systemic inflammation. • Routine assessment of SII index may improve disease monitoring in PMR, supporting its integration into clinical evaluation alongside established disease activity scores.