ABSTRACT

Numerous unrelated etiologies and pathogenetic pathways may manifest as inflammation of vessels. For the systemic vasculitides, the range of morphological findings is narrower than the clinical spectrum. Morphology is thus only partially reflective of underlying mechanisms and clinical manifestations (1). A certain inflammatory pattern may denote several diseases. Conversely, a given clinical disease or syndrome may manifest itself by more than one inflammatory pattern. Leukocytoclastic vasculitis (LCV) as a pathological finding exemplifies this lack of specificity. Leukocytoclastic vasculitis may be identified in such unrelated diseases as drug-induced hypersensitivity vasculitis, Henoch-Schonlein purpura, and Wegener's granulomatosis (2). By the same token, the disease giant cell (temporal) arteritis may manifest itself in the biopsy specimen as a transmural granulomatous infiltrate with giant cells or as a nondescript lymphocytic infiltrate in the outer arterial media and adventitia. In diagnostic pathology, therefore, familiarity with the anatomical distribution, vessel size and type, clinical features, and mjcroscopic findings is a prerequisite for meaningful diagnostic interpretation of vasculitic diseases. All parameters must be evaluated and correlated with the morphology before formulating a histopathological diagnosis. A tissue diagnosis that flies in the face of clinical impression is usually wrong. The pathologist's role in the diagnosis of vasculitides is twofold:

1. To confirm the presence or absence of inflammatory injury 2. To characterize and classify the pattern of injury It is a tenet in the histopathological diagnosis of nonneoplastic diseases that specimens

should be initially examined and the pattern of injury determjned without prior knowledge of clinical data. The absence of specific and pathognomonic features in most biopsy specimens may lead an already biased pathologist to merely reinforce a clinical impression and possibly perpetuate diagnostic errors. Nevertheless, a definitive diagnosis should never be formulated without correlation with clinical and laboratory findings and consultation with attending physicians. The following review deals with the pathology of the major primary vasculitic syndromes as defined by the American College of Rheumatology in 1990 (3). Each of these clinical entities is discussed under the heading of the predominant histopathological pattern of injury associated with a disease or syndrome.