Which vessel size is primarily affected in polyarteritis nodosa?

• A. Small capillaries
• B. Medium-sized arteries
• C. Large arteries
• D. Veins

Answer: (B)

Polyarteritis nodosa preferentially involves medium-sized muscular arteries. The key feature is transmural inflammation with fibrinoid necrosis of the arterial media, which creates aneurysms and segments of occlusion that disrupt blood flow to organs. This size-focused pattern explains why kidneys and mesenteric organs are commonly affected, producing hypertension and abdominal pain, while tiny vessels (capillaries, venules) are not the primary targets and large arteries are less typically involved.