How are vasculitides classified according to vessel size and primary versus secondary causes?

Classification of Vasculitis

Vasculitides are classified primarily by the size of the predominant vessel involved (small, medium, or large) and secondarily by whether they are primary (idiopathic) or secondary to other conditions such as infections, drugs, autoimmune diseases, or malignancies. 1, 2

Classification by Vessel Size

Large Vessel Vasculitis

• Large vessels refer to the aorta and its major branches 3
• The primary forms include:
  • Giant cell arteritis (GCA) 1, 3
  • Takayasu arteritis (TAK) 1, 3
• Isolated aortitis represents a single-organ variant 3

Medium Vessel Vasculitis

• Medium vessels refer to the main visceral arteries and veins and their initial branches 3
• The primary forms include:
  • Polyarteritis nodosa (PAN) 1, 4
  • Kawasaki disease 4, 3

Small Vessel Vasculitis

• Small vessels include arterioles, capillaries, and venules 1
• This category is further subdivided into:

ANCA-Associated Vasculitides (AAV):

• Granulomatosis with polyangiitis (formerly Wegener granulomatosis) 1, 5, 6
• Microscopic polyangiitis (MPA) 1, 5, 6
• Eosinophilic granulomatosis with polyangiitis (formerly Churg-Strauss syndrome) 1, 6

Non-ANCA-Associated (Immune Complex-Mediated) Small Vessel Vasculitides:

• IgA vasculitis (Henoch-Schönlein purpura) - most common in children 2, 4
• Cryoglobulinemic vasculitis 1, 4
• Cutaneous leukocytoclastic angiitis - most common in adults 2, 4

Classification by Primary vs. Secondary Causes

Primary Vasculitides

• These are idiopathic systemic vasculitides without an identifiable underlying cause 4
• Approximately 50% of cutaneous vasculitis cases remain etiologically unexplained 2
• Classification is based on immunopathological features and vessel size involved 4

Secondary Vasculitides

Infectious triggers:

• Hepatitis B-associated polyarteritis nodosa 1
• Hepatitis C-associated cryoglobulinemic vasculitis 1
• Other viral, bacterial, or fungal infections 2

Drug-induced vasculitis 2

Vasculitis associated with autoimmune diseases (e.g., systemic lupus erythematosus, rheumatoid arthritis) 2

Malignancy-associated vasculitis 2

Important Clinical Considerations

Overlap Between Categories

• There is substantial overlap in vessel size involvement, and arteries of any size can potentially be affected in any of the three main categories 3, 7
• This overlap creates challenges for rigid classification schemes 7

Distinguishing Vasculitis from Vasculopathy

• It is critical to differentiate true vasculitides (inflammatory vessel disease) from vasculopathies (non-inflammatory vessel disorders), as they can manifest similarly but require different management 2

Additional Classification Features

Beyond vessel size, vasculitides can be characterized by:

• Presence or absence of granulomatous inflammation 4, 7
• Association with specific autoantibodies (particularly ANCA) 4, 5
• Demographic features and organ tropism 7
• Role of immune complexes in pathophysiology 4, 7