Unclassified vasculitis.

Vasculitides are a heterogeneous group of inflammatory disorders of the blood vessels. The etiology and pathogenesis of vasculitides is incompletely understood, and the nomenclature and classification of vasculitides remains a challenge. A number of vasculitides were not included in the Chapel Hill Consensus (CHC) Conference definitions, thus, have remained 'unclassified', but may be included in a revised version of the nomenclature, e.g. Goodpasture's syndrome. In other cases the term 'unclassified' implies 'unclassifiable', i.e. a vasculitis cannot be assigned to any of the known entities. Vasculitis-induced acral necrosis including giant cell arteritis of small arteries as well as isolated forms of intestinal vasculitis including granulomatous giant cell polyphlebitis may belong to this category of rare 'unclassified' vasculitides. In some entities the relationship between vasculitis and other manifestations remains unclear, e.g. in Behçet's disease and IgG4-related systemic disease. In this review the clinical and pathological aspects of 'unclassified' vasculitides are briefly discussed.