What is the current classification system for vasculitis according to the 2012 Revised Chapel Hill Consensus Conference nomenclature?

Current Classification of Vasculitis

The current classification system for vasculitis is based on the 2012 Revised Chapel Hill Consensus Conference (CHCC) nomenclature, which categorizes vasculitis primarily by the size of the predominantly affected vessels into large-vessel, medium-vessel, small-vessel, and variable-vessel vasculitis. 1, 2

Primary Classification Framework

The 2012 CHCC nomenclature organizes vasculitis into four main categories based on vessel caliber:

Large-Vessel Vasculitis (LVV)

• Affects the aorta and its major branches 3, 1
• Includes two subtypes:
  • Giant cell arteritis (GCA): Affects patients over 50 years old, involving supra-aortic vessels and extracranial carotid branches, particularly the superficial temporal artery 3
  • Takayasu arteritis (TAK): Predominantly affects young women (≤40 years old) with preferential involvement of the aorta 3

Medium-Vessel Vasculitis (MVV)

• Affects main visceral arteries and their initial branches 3, 1
• Primary entity is polyarteritis nodosa (PAN) 1
• The 1994 Chapel Hill Conference restricted the term "polyarteritis nodosa" to arteritis in medium-sized and small arteries without involvement of smaller vessels, explicitly excluding patients with glomerulonephritis 4

Small-Vessel Vasculitis

• Affects intraparenchymal vessels, arterioles, venules, and capillaries 3, 1
• Subdivided into two major categories:
  • ANCA-associated vasculitis: Including granulomatosis with polyangiitis (GPA, formerly Wegener's), microscopic polyangiitis, and eosinophilic granulomatosis with polyangiitis (EGPA, formerly Churg-Strauss) 1, 5
  • Immune complex small-vessel vasculitis: Including cryoglobulinemic vasculitis and IgA vasculitis (Henoch-Schönlein purpura) 1

Variable-Vessel Vasculitis

• A new category introduced in the 2012 CHCC nomenclature 2
• Includes Behçet's disease and Cogan's syndrome 2
• Characterized by no predominance of any particular vessel size involvement 3

Key Advances in the 2012 Revision

Separation of ANCA-Associated Forms

• The 2012 nomenclature separated ANCA-associated vasculitis as a distinct group from immune complex small-vessel vasculitis, reflecting advances in understanding etiopathology 5

Expansion to Include Secondary and Single-Organ Vasculitis

• The classification was expanded beyond primary systemic vasculitis to include secondary vasculitis and single-organ vasculitis 2
• Cutaneous leukocytoclastic angiitis is restricted to vasculitis confined to the skin without involvement of other organs 4

Systematic Naming Conventions

• Eponyms have been replaced with systematic names where consensus was achieved: granulomatosis with polyangiitis (Wegener's) and eosinophilic granulomatosis with polyangiitis (Churg-Strauss) 5

Clinical Application Considerations

Vessel Size Overlap

• Important caveat: There is overlap between vasculitis types; LVV predominantly involves large vessels but can also affect medium and small vessels 3
• Variable-vessel vasculitis specifically addresses conditions without predominant vessel size involvement 3

Diagnostic Implications

• Tissue biopsy of large or medium vessels is often not feasible, making imaging crucial for diagnosing these vasculitides 3
• The classification strongly influences clinical presentation: PAN causes subcutaneous nodules and livedo racemosa without glomerulonephritis, while small-vessel vasculitis causes palpable purpura and may cause glomerulonephritis 6

Treatment Stratification

• Treatment is tailored to the specific type and severity of vasculitis to reduce morbidity and mortality 1
• Severity assessment evaluates the extent of organ involvement to determine treatment intensity 1