Pathological features of classical polyarteritis nodosa: analysis of 19 autopsy cases.

Classical polyarteritis nodosa (cPN) is a rare autoimmune disease featuring systemic inflammation of middle- and small-sized arteries. Because most of autopsy cases underwent clinical treatment, arterial fibrinoid necrosis, which is the most specific finding of cPN, is often obscure. The aim of this study was to seek morphological characteristics of the middle-sized arteries in autopsy cases of cPN, and to identify immunohistochemical markers for the diagnosis of cPN. Nineteen patients who had undergone autopsy with a diagnosis of cPN were enrolled. Twenty-one autopsy cases without cPN were examined as control group. Arterial fibrinoid necrosis in medium-sized arteries was observed in 8/19 autopsy cases. Elastica van Gieson staining showed an increased number of elastic fiber layers (P<0.0001) and greater distances between elastic fiber layers (P<0.0001) in the renal middle-sized arteries of the cPN group. These findings probably reflected the post-inflammatory remodeling process after necrotizing vasculitis. On immunohistochemical examination, the cPN group showed high matrix metalloproteinase-1 and tumor necrosis factor-α expressions and decreased smoothelin expression in the vascular wall compared to the control group. When uncertain or atypical autopsy cases of cPN are examined, these findings can help to make the pathological diagnosis of cPN.