MPO and microscopic polyangiitis: In most patients with MPA and/or SSc with AAV, high titers of MPO-ANCA are associated with disease activity, rises in MPO-ANCA titers precede relapses, and even a case of MPO-ANCA seroconversion associated with fulminant vasculitis in antitopoisomerase-1 antibody positive SSc has been reported [31], but MPO-ANCA titers do not necessarily correlate with disease activity or vasculitis syndrome.