The vasculitides are a heterogeneous group of systemic inflammatory disorders characterized by inflammation of blood vessels.1 Vascular inflammation may cause vessel narrowing or occlusion leading to tissue ischemia or infarction, or may result in vessel rupture with subsequent hemorrhage. These effects underlie the significant morbidity and mortality associated with the vasculitides.
The various forms of vasculitis differ in regard to the size, type, and distribution of involved vessels. Vessel size alone is inadequate to distinguish between the vasculitides. Consequently, nomenclature and classification schemes also rely on the nature of the inflammatory lesion (e.g., granulomatous, leukocytoclastic, eosinophilic) and the organ systems that are most frequently affected (e.g., ear, nose, sinus, lung, kidney).1 Inflammatory injury in these disorders may also occur in the absence of vasculitis.
Diagnostic Approach to Vasculitis
Even when a diagnosis of vasculitis has been clearly established on clinical and pathologic grounds, it must be determined whether the vasculitis is caused by a primary (idiopathic) vasculitic disorder or a secondary form of vasculitis. Secondary forms of vasculitis for which the etiology is known include: vasculities complicating a wide variety of viral, bacterial, mycobacterial, fungal, and other infectious agents; vasculitis caused by drug or toxin exposure; malignancies (paraneoplastic, embolic, invasive); and embolic (cholesterol) debris. Other secondary forms of vasculitis for which the etiology may lack details of factors such as vasculitis complicating other rheumatic disorders such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), Sjogren's syndrome, and Behçet's disease (BD) that are secondary idiopathic forms of vasculitis.
The diagnosis of vasculitis stands challenging for a number of reasons. While vasculitis must be considered in the differential diagnosis of any patient with an unexplained multisystem illness or fever of unknown origin, most of the individual forms of vasculitis are uncommon. Early diagnosis of primary vasculitis is critical to ensure that when indicated, prompt and effective immunosuppressive treatment is instituted to minimize the significant morbidity and mortality associated with these disorders. In the diagnostic process, it is also essential to consider secondary forms of vasculitis and diseases that mimic vasculitis such as infectious (e.g., infective endocarditis), neoplastic and paraneoplastic, iatrogenic, genetic (e.g., Ehler-Danlos syndrome type IV, Marfan's syndrome), atheroembolic, vasospastic (e.g., caused by cocaine, amphetamine, and their derivatives), and other vascular disorders. Immunosuppressive therapy may have adverse and potentially fatal consequences in these disorders.
The diagnostic exercise combines information of several types: clinical phenotype, laboratory data, imaging abnormalities, and histopathologic characteristics. While histopathologic proof is often desirable, it may not be feasible as in the case of large vessel vasculitis (e.g., Takayasu's arteritis [TAK]), coronary vasculitis (e.g., Kawasaki's disease [KD]), or ischemic colitis in the absence of surgical indications (e.g., BD, polyarteritis nodosa [PAN], or vasculitis complicating inflammatory bowel disease).
When considering vasculitis in general, patients may present with impressive but nonspecific symptoms such as fatigue, weakness, malaise, fevers, sweats, anorexia, weight loss, ...