Why is separating out ANCA associated vasculitis from Relapsing Polychondritis important?
Several clinical features overlap between ANCA-associated vasculitis and RPC including ocular involvement (episcleritis, scleritis, orbital inflammatory disease), airway disease, and articular or auricular involvement. Low-titer ANCA antibodies can be seen in approximately 10% of true RPC as well, further contributing to difficulty in distinguishing these two conditions. Low-titer ANCA positivity in patients with RPC most often lack myeloperoxidase (MPO) and proteinase 3 (PR3) specificity, and more specific clinical features of ANCA-associated vasculitis such as cavitary lung lesions and characteristic biopsy findings (granulomatous inflammation, tissue necrosis, and vasculitis) should be absent. Distinguishing among these two conditions is important not only for prognosis but also for treatment as case reports suggest a poor response to rituximab therapy in RPC
