Anatomic Pathology: Vascular Pathology

• Overall, approximately 85% to 90% of patients with untreated pauciimmune small vessel vasculitis are found to be ANCA positive.

• Eosinophilic granulomatosis with polyangiitis (formerly known as Churg-Strauss syndrome), considered one of the three major ANCA-associated small vessel vasculitides, shows ANCA positivity in only 60% of cases.

• The antigen specificity of ANCA correlates to some degree with the category of pauciimmune small vessel vasculitis; however, overlap is significant so that the specificity alone cannot be used to differentiate between the three major entities of microscopic polyangiitis, granulomatosis with polyangiitis, and eosinophilic granulomatosis with polyangiitis.

• Patients who present with classic clinical findings of pauciimmune small vessel vasculitis but have negative ANCA serologies are often classified as having ANCA-negative pauciimmune small vessel vasculitis.

• In the setting of ANCA negativity, PAN involving small arteries should be included in the differential diagnosis. If involvement of capillaries and venules is also found on a biopsy specimen, PAN can be ruled out, and diagnosis of ANCA-negative pauciimmune small vessel vasculitis can be made.

Jennette JC: Nomenclature and classification of vasculitis: lessons learned from granulomatosis with polyangiitis (Wegener’s granulomatosis). Clin Exp Immunol 2011;164(Suppl 1):7-10.

Jennette JC: Renal involvement in systemic vasculitis.In Jennette JC, Olson JL, Schwartz MM, et al (eds): Heptinstall’s Pathology of the Kidney, 5th ed. Philadelphia: Lippincott-Raven, 1998, p 1059.

Jennette JC, Wilkman AS, Falk RJ: Diagnostic predictive value of ANCA serology. Kidney Int 1998;53(3):796-798.

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