[Polyangiitis overlap syndrome].

Polyangiitis overlap (PO) syndrome is a relatively new syndrome proposed by Leavitt and Fauci in 1986 (1). They noticed there are several patients who do not belong to a single disease entity of the already established vasculitis and show systemic manifestations seen in more than two diseases. They called these patients as having PO syndrome. PO syndrome also contained unclassified systemic necrotizing vasculitis in the original paper. Although there are various combinations of vasculitis, the most common type of PO syndrome is the overlap of classical polyarteritis nodosa and Churg-Strauss syndrome. The prognosis of PO syndrome is not so bad. The majority of the patients experienced remissions after the treatment with corticosteroid and cyclophosphamide.