Antineutrophil cytoplasmic antibodies: two cases of changing antigenic specificity.

The transformation of the antineutrophil cytoplasmic antibody (ANCA) specificity in the absence of specific drug treatment has not been reported in the literature. A few studies have suggested changes in the epitopes recognized by the ANCAs. We describe two patients who switched from myeloperoxidase-positive to PR3 (proteinase 3)-positive ANCA during the course of their disease process and subsequently remained unchanged. One patient developed ulcerative colitis following the appearance of PR3-ANCA while the other remains quiescent. Regular follow-up and close monitoring of ANCA specificity are essential. A change of specificity may indicate the development of a new ANCA-related disease.