Re-examination of features to distinguish polyarteritis nodosa from superficial thrombophlebitis

The correct identification of vessel type is crucial in distinguishing cutaneous polyarteritis nodosa from superficial thrombophlebitis. As the treatment and prognosis of these conditions are very different, correct diagnosis is critical, but they have overlapping clinical and histopathologic features, which can sometimes make the distinction difficult. Features commonly used to distinguish an artery from vein include vessel shape and diameter, the presence or absence of an internal elastic lamina, smooth muscle pattern, and the presence or absence of valves. Recently, it has been proposed that the amount and distribution of elastic fibers in the medial muscular layer are the most reliable features to make this distinction. The first part of this study used prosector-identified vessels to determine which of these features is most sensitive and specific for identifying an artery and vein. A total of 19 arteries and 16 veins were dissected from autopsy and amputation specimens. For each specimen, the smooth muscle pattern, elastic fiber pattern, the presence of valves, and the presence or absence of an internal elastic membrane were determined. The quantity of elastic fibers in the muscular wall of each sample was also determined. Although the elastic fiber pattern was the most specific feature in identifying a vein, it suffered from low sensitivity (43.8%). The smooth muscle pattern had the highest combined sensitivity and specificity. In the second part of this study, the histologic features listed above were examined in previously diagnosed cases of superficial thrombophlebitis and arteritis. When inflammation is present within and around the wall of the vessel, all of the studied histologic features become less reliable, and the interobserver reliability of distinguishing arteritis from thrombophlebitis was low. Our findings suggest that no single histopathologic feature is completely reliable and combining the histopathologic features with clinicopathologic correlation is essential for correct vessel identification.