In a patient with recurrent episodes of GCA that flare shortly after steroid tapering, how do you differentiate between steroid-dependent inflammatory relapse, an alternative autoimmune vasculitic process, and a paraneoplastic phenomenon?

This could certainly be worrisome for a paraneoplastic phenomenon. GCA is associated disproportionately with myeloid lineage mutations (CHIP - clonal hematopoiesis of indeterminate significance). TET2 is think is the best-studied mutation, but in my experience, any other CHIP mutations such as ASXL1, DNMT3A, SRSF2, etc can also do it. From a clinical standpoint, this makes GCA occur more frequently in patients with MDS and other myeloid lineage cancers (I’ve seen polycythemia vera, essential thrombocythemia, and CMML present simultaneously with the GCA).

However, GCA is a challenging diagnosis to make, and there are many mimics. If you are sure that the “episodes of GCA” are truly vasculitic, then I would re-analyze the temporal artery biop...

Paraneoplastic disease rarely behaves like GCA with ischemic manifestations. If a non-GCA vasculitis is suspected, perhaps repeat biopsy or serologic testing for other markers could be done. I'm not sure of the value of these tests, however, given that the treatment approach with immunosuppression would probably be the same.