Distinguishing polyarteritis nodosa from microscopic polyangiitis and implications for treatment.

The vasculitides are a heterogeneous group of disorders for which classification is needed to facilitate diagnosis and treatment. Recent studies based on a more comprehensive clinical analysis of symptoms and virologic investigations favor the recognition, in the polyarteritis nodosa (PAN) group, of a distinct form of systemic vasculitis called microscopic polyangiitis (MPA). This distinction may be confusing, so the features of each condition need to be more precisely defined. Differentiation between PAN and MPA cannot be based on only histologic criteria. Clinical manifestations (especially lung and kidney involvement), biologic signs (antineutrophil cytoplasmic antibodies and hepatitis B and C infection), and angiographic data must be taken into consideration. Therapeutic strategy should differ dramatically, depending on whether primary or secondary MPA or PAN has been diagnosed, and treatment optimization is certainly the best reason for improving the classification of the systemic vasculitides.