Approach to systemic vasculitis.

Systemic vasculitis is a confusing subject which has been difficult to classify and understand. Improvements in therapy increase the importance of early diagnosis. This paper reviews the clinical and pathological differences of the systemic vasculitides, and a working approach to the differential diagnosis of vasculitis is formulated based on the size of the vessel involved. Vessel size and histopathology determine to what group of diseases a particular syndrome belongs, thereby allowing subclassification and a more rational approach to management.