Small Vessel Vasculitis

Small vessel vasculitis is the category of vasculitides that predominantly affects small intraparenchymal vessels — small arteries, arterioles, capillaries, and venules. The Chapel Hill nomenclature divides it into ANCA-associated vasculitis (granulomatosis with polyangiitis, microscopic polyangiitis, and eosinophilic granulomatosis with polyangiitis) and immune-complex small vessel vasculitis (such as IgA vasculitis and cryoglobulinaemic vasculitis).

Definition

Small vessel vasculitis is vasculitis predominantly affecting small intraparenchymal vessels (small arteries, arterioles, capillaries, and venules), divided into ANCA-associated and immune-complex forms, per the 2012 Revised Chapel Hill Consensus Conference nomenclature.

Scope

The entry covers the definition of small vessel vasculitis, its two major mechanistic subsets (pauci-immune ANCA-associated and immune-complex-mediated), the entities within each, and how the 2022 ACR/EULAR criteria classify the ANCA-associated forms. It is a reference topic and does not provide diagnostic or treatment instructions.

Core questions

• Which small-vessel beds are involved, and how do skin, lung, and kidney manifestations arise?
• How does pauci-immune (ANCA-associated) vasculitis differ from immune-complex vasculitis?
• What entities fall under each subset, and how do they overlap clinically?
• How do the 2022 ACR/EULAR criteria classify the ANCA-associated forms?

Key concepts

• Pauci-immune vasculitis
• ANCA-associated vasculitis
• Granulomatosis with polyangiitis
• Microscopic polyangiitis
• Eosinophilic granulomatosis with polyangiitis
• Immune-complex vasculitis (IgA, cryoglobulinaemic)
• Pulmonary-renal syndrome
• Leukocytoclastic vasculitis

Mechanisms

Small vessel vasculitis damages capillaries, venules, arterioles, and small arteries, producing palpable purpura, alveolar haemorrhage, and rapidly progressive glomerulonephritis depending on the territory. In ANCA-associated (pauci-immune) forms, little immunoglobulin deposits in vessel walls, and antineutrophil cytoplasmic antibodies are thought to activate primed neutrophils to injure the endothelium; granulomatosis with polyangiitis is characteristically granulomatous, microscopic polyangiitis is not, and eosinophilic granulomatosis with polyangiitis features eosinophilia and asthma. In immune-complex forms, deposition of immunoglobulin and complement (for example IgA in IgA vasculitis, or cryoglobulins) drives the inflammation.

Clinical relevance

Small vessel vasculitis is the reference category for vasculitis of the smallest vessels and accounts for many cases of pulmonary-renal syndrome and cutaneous vasculitis encountered in the literature. Distinguishing pauci-immune from immune-complex mechanisms underpins how clinicians interpret biopsy and serology findings. This entry characterises the disease category for educational reference and is not a basis for individual diagnosis or treatment.

Epidemiology

The ANCA-associated vasculitides are individually rare, presenting most often in middle and older age; MPO-ANCA disease is relatively more common in some Asian populations and PR3-ANCA in parts of Northern Europe. IgA vasculitis is the most common vasculitis of childhood, while cryoglobulinaemic vasculitis is frequently associated with hepatitis C infection. Reported rates depend on the criteria and ascertainment used.

Evidence & guidelines

The 2012 Revised Chapel Hill Consensus Conference defines the category and its subsets, the 2022 ACR/EULAR classification criteria operationalise granulomatosis with polyangiitis and microscopic polyangiitis for study, and the EULAR recommendations summarise management evidence for ANCA-associated vasculitis. These documents frame how small vessel vasculitis is recognised and classified.

History

The distinction between immune-complex and pauci-immune small vessel vasculitis emerged with the discovery of antineutrophil cytoplasmic antibodies in the 1980s, which clarified the relationship among granulomatosis with polyangiitis, microscopic polyangiitis, and eosinophilic granulomatosis with polyangiitis. The Chapel Hill nomenclature consolidated these into the ANCA-associated and immune-complex categories, and the 2022 ACR/EULAR criteria provided contemporary classification definitions.

Key figures

• J. Charles Jennette
• Ronald J. Falk
• Friedrich Wegener
• Peter A. Merkel

Seminal works

• jennette-2012
• robson-2022
• suppiah-2022
• hellmich-2024

Frequently asked questions

What are the two main subsets of small vessel vasculitis?

ANCA-associated (pauci-immune) vasculitis — granulomatosis with polyangiitis, microscopic polyangiitis, and eosinophilic granulomatosis with polyangiitis — and immune-complex small vessel vasculitis, such as IgA vasculitis and cryoglobulinaemic vasculitis.

What does 'pauci-immune' mean?

It describes vasculitis in which little or no immunoglobulin is deposited in the vessel wall, a hallmark of the ANCA-associated small vessel vasculitides, in contrast to immune-complex forms with prominent deposition.