Vasculitis.

Vasculitis is defined by the presence of blood vessel inflammation. It can be observed in a wide variety of settings, which can be broadly grouped as secondary vasculitides, which occur in association with an underlying disease or trigger, or primary vasculitides, in which vasculitis is occurring for as-yet unknown causes. The primary systemic vasculitides comprise a range of disease entities that are uniquely identified by their clinical, histopathologic, and therapeutic characteristics. Individual diseases predominantly affect blood vessels of a particular size, which influences their clinical manifestations and has been used in their classification. The vasculitides can also differ in their severity, extending from self-limited illnesses to those that can be life-threatening in the absence of prompt initiation of treatment. Immunosuppressive agents are used to treat many vasculitic diseases. Although such approaches can be effective, the patient's long-term course can be influenced by organ damage from their initial presentation, disease relapses, and medication toxicity. Recent investigations have focused on understanding disease pathophysiology and the exploration of novel therapeutic approaches.