Clinical features and diagnosis of small-vessel vasculitis.

Vasculitis is inflammation of the blood vessel. Granulomatosis with polyangiitis (GPA), microscopic polyangiitis, and eosinophilic GPA are three small-vessel vasculitic diseases that share certain features, but also have important differences. Distinguishing these entities may influence the diagnostic approach, treatment decisions, and outcomes. Circulating antineutrophil cytoplasmic antibodies (ANCA) characterize all three diseases, although their immunofluorescence patterns and target antigen specificities differ. While the presence of ANCA can suggest these diagnoses, the diseases are best viewed as separate entities, each defined by specific clinical and histologic characteristics.