Morphologic differences between polyarteritis and Wegener's granulomatosis using light, electron and immunohistochemical techniques.

The differential diagnosis of renal biopsies of patients with polyarteritis nodosa (PAN) versus those with Wegener's granulomatosis (WG) is difficult because in both the morphologic expression is a focal proliferating and necrotizing glomerulonephritis (GN) with crescents. Twenty-nine biopsies of PAN and 29 of WG were studied by light, electron microscopy and immunohistochemistry. Whereas in PAN the dominent feature is severe focal fibrinoid necrosis of glomerular tufts, WG is characterized by destructive extracapillary GN with capsular breaks and periglomerulitis leading to complete glomerular destruction and replacement by a localized inflammatory exudate in the form of a granuloma. In PAN necrotizing arteritis is common (19 of 29), whereas only 1 of 29 cases of WG showed arteritis. Depending on the stage of the disease, various types of hematogenous cells can be seen in both. In general, the dominent cell type in PAN is polymorphonuclear cells (PMNs) with or without eosinophils, whereas in WG mononuclear cells dominate the picture. Monocytes and macrophages, including giant cells in the crescents, periglomerular infiltrates, and in the granulomas are seen, whereas in the interstitium, plasma cells predominate. The histologic ultrastructural and immunohistochemical findings in both groups will be discussed.