Polyangiitis overlap syndrome. Classification and prospective clinical experience.

Ten patients were prospectively studied who had features of systemic vasculitis that could not be classified into one of the well-defined vasculitic syndromes. Since many of these syndromes had overlapping features of several distinct vasculitides, they were classified as the polyangiitis overlap syndrome. Cutaneous disease was common (nine of 10 patients) and, some patients, had been mistakenly diagnosed as "hypersensitivity" or isolated cutaneous vasculitis. The polyangiitis overlap syndrome is a systemic vasculitis, and all of the patients required therapy with cyclophosphamide (2 mg/kg per day). Nine of 10 patients were also treated with corticosteroids, which were administered initially on a daily basis followed by an alternate-day regimen. A complete remission was induced in all of the patients, with a mean follow-up duration of 58.4 months. In eight of 10 patients, remission was maintained following discontinuation of cyclophosphamide. The mean duration of remission was 45.9 months, with a mean interval after discontinuation of all therapy of 22.3 months. Two patients had relapses after the immunosuppressive therapy was discontinued; however, complete remissions were reinduced following reinstitution of therapy.