S8C1-VASCULITIDES

SECTION 8

Chapter 1 (HOME)

Richard J. Reed, M.D., New Orleans, LA

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Vasculitides

The morphologic definition of a vasculitis is inconsistent. Many students, with an interest in the problems, place emphasis on: 1.) evidence of damage to the walls of vessels, 2.) perivascular infiltrates of neutrophils, and 3.) leukocytoclasia; in public, they will vehemently deny the existence of a vasculitis in which the reacting cell is a lymphocyte. In practice, these same students will accommodate certain histologic patterns in the category of a “lymphocytic vasculitis.” They might also diagnose certain patterns as leukocytoclastic vasculitis in the absence of histologic evidence of actual damage to the walls of vessels. Often, in lesions (which these students are willing to classify as a vasculitis) infiltrates of neutrophils will be preponderantly interstitial among collagen bundles of the reticular dermis with little evidence of actual damage to the walls of vessels; in some other case, with more extensive and diffuse interstitial infiltrates of neutrophils among collagen bundles, the lesion is likely to be characterized as a “neutrophilic dermatosis” (Sweet’s syndrome); it will differ from the “vasculitic” counterpart only in degree of infiltration. On the other hand, some examples of neutrophilic dermatosis with the clinical presentation of Sweet’s syndrome, will be associated with fibrinoid necrosis of vessel walls. The clinical presentation then is likely to be given precedence; the vascular alterations will then be accommodated in the category of Sweet’s syndrome, rather than vasculitis, or pyoderma gangrenosum. Recently, examples of “pyoderma gangrenosum,” lacking evidence of fibrinoid necrosis of vessels, have been described.

Much has been made of the utility of an evaluation of the distribution of inflammatory infiltrates in the dermis, with great emphasis on the relationship between the infiltrates and the extent of involvement along the adventitia of vessels. From a different perspective, if epidermal patterns and the distribution of inflammatory cells in the setting of leukocytoclastic angiitis are compared with those processes showing somewhat similar patterns in which the reacting cell is a lymphocyte (i.e., the only distinction being that the reacting cells are lymphocytes), there are lesions, which on the basis of similarities, would qualify as “lymphocytic vasculitis.” Lesions of the latter type commonly are associated with the extravasation of red blood cells into the dermis. The patterns, in regard to the distribution of inflammatory cells, are “vasculitic” in character. The common features include both a relatively normal epidermis and perivenular infiltrates of lymphocytes. The perivenular infiltrates, in such examples, are distributed almost exclusively along vessels, often in the superficial portion of the reticular dermis (with relative sparing of the papillary dermis and the epidermis). There is utility in the concept of “lymphocytic vasculitis.”

It is possible to approach the vasculitides (angiitic angiopathies) as problems in the laboratory study of the effects of immune complexes; in such an approach, the rigid morphologic definition of vasculitis, that is currently favored and defended, may not be in accord with the histologic patterns associated with some examples of immune complex disease. If the definition of vasculitis were to be restricted to examples in which vessels show areas of necrosis, there would be both lymphocytic and neutrophilic variants. Lesions with infiltrates mostly of an interstitial nature, in which inflammatory cells infiltrate the reticular dermis among collagen bundles qualify as either lymphocytic or neutrophilic collagenoses. Examples of neutrophilic collagenosis, in which damage to the walls of vessels (it should be noted that the endothelium of affected vessels in vasculitides, Sweet’s syndrome, and pyoderma gangrenosum generally remains viable, even in the face of prominent fibrin deposits in the adventitia of vessels) is also a feature, qualify as neutrophilic collagenoses with vasculitis. Depending on clinical presentation, some problem lesions could then be characterized as vasculitis, some as Sweet’s syndrome, and some as pyoderma gangrenosum (admitting that there are significant overlaps in histologic patterns).

This section is devoted to a discussion of various vasculitides.