Purpose of review: To clearly define single-organ vasculitis (SOV) and distinguish diffuse from focal SOV. To delineate clinical, laboratory, and histopathological features useful in differentiating focal SOV from systemic vasculitis affecting the same territory.
Recent findings: SOV may affect organs in a diffuse or multifocal fashion (e.g. central nervous system and skin) or may be confined to focal sites (e.g. breast, gynecologic, testicular, and abdominal structures, and the aorta). Because the territories affected in SOV may also be targeted in systemic vasculitis, the diagnosis of SOV should be applied when it is clear that vascular inflammation is not present in other sites at the time of diagnosis as well as during follow-up surveillance, which has arbitrarily been recommended to be of at least 6 months. Once the diagnosis of SOV is confirmed, terms used for systemic vasculitides should be avoided (e.g. polyarteritis of the testes). Focal SOV is often incidentally found in the course of biopsies or surgery for suspected malignancy, infection, or structural abnormalities. In focal SOV, resection of the inflammatory lesion alone may be curative, whereas systemic therapy is almost always required for diffuse forms of SOV.
Summary: SOV definition implies vascular inflammation confined to an isolated organ. This diagnosis always requires exclusion of systemic illness. In focal forms of SOV, certain clinical, laboratory, and pathologic features assist the clinician in distinguishing isolated from systemic vasculitis, and consequently in devising therapeutic and surveillance strategies.