How would you treat a young patient who presents with coronary vasculitis and aortitis with persistently positive MPO but no other features of AAV?

Once infectious causes such as syphilis have been excluded, the most common causes of the combination of aortitis and coronary vasculitis would be Takayasu arteritis and IgG4RD. However, AAV can cause both aortitis and coronary vasculitis (albeit infrequently). Therefore, if there are no features of IgG4RD (which can certainly overlap with AAV) and the MPO-ANCA is persistently positive (and the patient is not on any medication that can induce an MPO-ANCA), it would be reasonable to treat this patient as AAV and monitor for response.

This is a difficult question for anyone to provide complete guidance since you are asking about treatment. The first question a provider has to ask is whether the treating doctor feels this is sufficient evidence to diagnose ANCA-associated vasculitis. All of us would love to invoke Takayasu arteritis, but we all agree there is no evidence of MPO occurring in this disorder. So, if the treating doctor wishes to invoke this diagnosis, that doctor would have to accept the MPO as a false positive. It would be helpful to know the MPO titer, as well as its association with pANCA. Were there eosinophils or elevated IgE levels? I assume not, otherwise, it would have been listed.

Treatment of these presentations requires attention to the presence of...