Clinical implications of peripheral eosinophil count at diagnosis in patients newly diagnosed with microscopic polyangiitis and granulomatosis with polyangiitis

Abstract

Background This study investigated the clinical implications of peripheral eosinophil count at diagnosis in estimating cross-sectional antineutrophil cytoplasmic antibody-associated vasculitis (AAV) activity and predicting all-cause mortality during follow-up in patients newly diagnosed with microscopic polyangiitis (MPA) and granulomatosis with polyangiitis (GPA). Methods This study included 224 immunosuppressive drug-naïve patients with peripheral eosinophil count at diagnosis < 1,000/mm3. The Birmingham Vasculitis Activity Score (BVAS), the Five-Factor Score (FFS), erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) at diagnosis were assessed. Results The median age of the 224 patients (152 MPA and 72 GPA) was 62.0 years; 35.3% of them were men. At diagnosis, peripheral eosinophil count was significantly correlated with BVAS (P = 0.001), FFS (P = 0.046), ESR (P < 0.001), and CRP (P < 0.001). Deceased patients had a significantly higher median peripheral eosinophil count at diagnosis than surviving patients (310.0/mm3 vs. 170.0/mm3, P = 0.004). In addition, patients with MPA and those with cardiovascular and renal manifestations at diagnosis exhibited significantly higher peripheral eosinophil counts than those without. When the optimal cut-off of peripheral eosinophil count at diagnosis for all-cause mortality during follow-up was set at 175.0/mm3, Patients with peripheral eosinophil count at diagnosis ≥ 175.0/mm3 exhibited a significantly lower cumulative patients’ survival rate than those with peripheral eosinophil count at diagnosis < 175.0/mm3 (P = 0.008). Conclusions This study was the first to demonstrate that peripheral eosinophil count at diagnosis could estimate cross-sectional AAV activity at diagnosis and contribute to predicting all-cause mortality during follow-up in MPA and GPA patients.