Summary

• Rare form of systemic vasculitis that affects only medium-sized vessels (i.e., small and medium-sized arteries).
• Hepatitis B virus (HBV)-related PAN has become very rare since the introduction of effective immunisation programmes against the virus.
• Both non-HBV-related PAN and HBV-related PAN are differentiated from the other small- and medium-vessel vasculitides by the absence of anti-neutrophil cytoplasmic antibodies, and by confirmation that small vessels (i.e., arterioles, capillaries, venules) are not involved.
• Angiography typically demonstrates microaneurysms and focal narrowing in medium-sized blood vessels.
• Pathology is characterised by focal and segmental transmural necrotising inflammation with fibrinoid necrosis in medium-sized vessels.
• Treatment for non-HBV-related PAN is based on immunosuppression with corticosteroids and cyclophosphamide.
• Treatment for HBV-related PAN utilises a short course of high-dose corticosteroids, followed by a combination of antiviral therapy and plasma exchange.
• Prognosis can be determined by use of the 5-factor score.