Pathophysiology
1) systemic necrotizing vasculitis of small- and medium-sized arteries 2) mostly affects renal, hepatic, and visceral arteries 3) variants – classic polyarteritis nodosa, microscopic angiitis, and Churg-Strauss variant; much overlap among variants 4) classic finding – development of multiple aneurysms along the involved arteries
Signs and Symptoms
1) hypertension 2) renal failure 3) myalgia 4) arthralgia 5) peripheral neuropathy (polyneuropathy multiplex) 6) abdominal pain 7) nausea and vomiting 8) infarction of viscera 9) subcutaneous (skin) red nodules 10) purpura and rash 11) cutaneous infarcts 12) congestive heart failure 13) myocardial infarction 14) fever 15) weight loss 16) headache 17) painful testes
Characteristic Test Findings
Laboratory – 1) increased leukocyte count 2) anemia 3) increased sed rate 4) positive p-ANCA (but much more common in microscopic angiitis variant) Radiology – 5) multiple aneurysms along affected arteries
Histology/Gross Pathology
1) segmental fibrinoid necrotizing inflammation and occlusion of small- and medium-size arteries, especially at branch points 2) microscopic angiitis – also associated with venitis and pulmonary and bronchial artery involvement (not seen in classic variant)
Associated Conditions
1) variants overlap and there is inexactness as to defining parameters of each disease 2) hepatitis B antigen occurs in 30% of cases of classic variant and hepatitis C antigen occurs in 5% 3) increased incidence in hairy cell leukemia
Biochemistry
likely immunologic component as circulating hepatitis B antigen/IgM complexes found in walls of affected blood vessels
Treatment
1) prednisone 2) cyclophosphamide 3) (vidarabine) antihepatitis B treatment 4) plasmapheresis 5) alpha-IFN
Tips for USMLE
1) if question mentions granulomas, it is not PAN 2) if eosinophils are mentioned, it is not PAN 3) if question mentions multiple aneurysms in hepatic, renal, or mesenteric arteries, think PAN (although this is not strictly pathognomonic)
