[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Blood vessels](https://durgical.com/en/general-pathology/areas/vessels/) › Immune-complex small-vessel vasculitis

# Immune-complex small-vessel vasculitis

- Lesion

Antibody–antigen clumps lodge in tiny vessels, mostly venules of the skin, and attract neutrophils: the result is purpura you can feel.

Updated Nov 12, 2026

## Key points

- Leukocytoclastic vasculitis: postcapillary venules with neutrophils, nuclear dust, fibrinoid necrosis and red-cell extravasation.
- Palpable purpura on the legs is the classic sign of small-vessel vasculitis.
- IgA vasculitis (Henoch–Schönlein): children after an upper respiratory infection; purpura of buttocks and legs, arthralgia, abdominal pain, IgA nephropathy-like glomerulonephritis.
- Cryoglobulinemic vasculitis: mixed cryoglobulins, mostly from hepatitis C; purpura, arthralgia, neuropathy, membranoproliferative glomerulonephritis, low C4.
- Behçet disease: recurrent oral and genital ulcers, uveitis, skin lesions and venous or arterial thrombosis and aneurysms; HLA-B51 association.

## What it is

When immune complexes are deposited in the walls of small vessels, complement is activated and neutrophils destroy the wall, breaking up as they do (leukocytoclasia). The skin shows palpable purpura; kidney, gut and joints may follow. Triggers include drugs and infections (hypersensitivity or cutaneous small-vessel vasculitis), IgA-containing complexes (IgA vasculitis), cryoglobulins linked to hepatitis C (cryoglobulinemic vasculitis) and autoimmune disease such as lupus. Behçet disease is a variable-vessel vasculitis that can affect arteries and veins of any size.

## Structure

- Skin biopsy: neutrophils in and around venule walls, nuclear debris, fibrin in the wall and extravasated red cells.
- Direct immunofluorescence: IgA in IgA vasculitis; IgM, IgG and C3 in cryoglobulinemia.

## Step by step

- An antigen (drug, microbe, autoantigen or IgA aggregates) forms complexes with antibodies in the blood.
- Complexes lodge in the walls of small vessels where flow is slow and permeability high (venules of the skin).
- Complement activation releases C5a, which attracts neutrophils.
- Neutrophils damage the wall and fragment; red cells leak into the tissue.
- If the antigen is removed, lesions heal in weeks; persistent antigen causes recurrent or chronic disease.

## Immune-complex and variable-vessel vasculitides

| Disease | Deposits or trigger | Organs | Clue |
| --- | --- | --- | --- |
| [Cutaneous small-vessel (hypersensitivity) vasculitis](https://durgical.com/en/conditions/cutaneous-small-vessel-vasculitis/) | Drug or infection immune complexes | Skin | Palpable purpura after a new drug |
| [IgA vasculitis](https://durgical.com/en/conditions/iga-vasculitis/) | IgA1-dominant complexes | Skin, joints, gut, kidney | Child, purpura on buttocks and legs |
| [Cryoglobulinemic vasculitis](https://durgical.com/en/conditions/cryoglobulinemic-vasculitis/) | Mixed cryoglobulins (IgM rheumatoid factor with IgG) | Skin, nerves, kidney | Hepatitis C, low complement |
| [Lupus vasculitis](https://durgical.com/en/conditions/systemic-lupus-erythematosus/) | DNA–anti-DNA complexes | Skin, kidney, brain | Positive antinuclear antibodies, low complement |
| [Behçet disease](https://durgical.com/en/conditions/behcet-disease/) | Neutrophil-driven, HLA-B51 associated | Mouth, genitals, eye, veins, arteries | Recurrent oral and genital ulcers |

## Clinical notes

- Many drug- or infection-triggered cases resolve when the trigger is removed.
- Kidney involvement determines the long-term outlook in IgA and cryoglobulinemic vasculitis.

## Memory aid

Complexes clog the skin's small drains, neutrophils burst on the spot, and the purpura can be felt with the fingertips.

## Test yourself

Think of the answer, then tap the question to see it.

## What does ‘leukocytoclastic’ mean?

That neutrophils in the vessel wall break apart, leaving nuclear dust (fragments) around damaged venules.

## Which infection is the usual cause of mixed cryoglobulinemic vasculitis?

Chronic hepatitis C virus infection.

## Which immunoglobulin is deposited in IgA vasculitis, and which organ decides the prognosis?

IgA (mainly IgA1); the kidney decides the long-term outlook.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/general-pathology/immune-complex-small-vessel-vasculitis/)

[More Pathology questions →](https://durgical.com/en/practice/?f=pathology)

## Elsewhere in DurgiPedia

- [Type III hypersensitivity (immune complexes)](https://durgical.com/en/immunology/type-iii-hypersensitivity/)
- [Complement: three pathways, MAC, regulators](https://durgical.com/en/immunology/complement-three-pathways-mac-regulators/)

## Connections

## Related 4

- [Vasculitis: classification and mechanisms](https://durgical.com/en/general-pathology/vasculitis-classification-and-mechanisms/)
- [ANCA-associated vasculitis](https://durgical.com/en/general-pathology/anca-associated-vasculitis/)
- [Patterns of necrosis: coagulative, liquefactive, caseous, fat, fibrinoid, gangrenous](https://durgical.com/en/general-pathology/patterns-of-necrosis-coagulative-liquefactive-caseous-fat-fibrinoid-gangrenous/)
- [Vascular bleeding disorders](https://durgical.com/en/general-pathology/vascular-bleeding-disorders/)

## Related conditions 6

- [Cutaneous small-vessel (leukocytoclastic, hypersensitivity) vasculitis](https://durgical.com/en/conditions/cutaneous-small-vessel-vasculitis/)
- [IgA vasculitis (Henoch–Schönlein purpura)](https://durgical.com/en/conditions/iga-vasculitis/)
- [Cryoglobulinemic vasculitis](https://durgical.com/en/conditions/cryoglobulinemic-vasculitis/)
- [Behçet disease](https://durgical.com/en/conditions/behcet-disease/)
- [Systemic lupus erythematosus](https://durgical.com/en/conditions/systemic-lupus-erythematosus/)
- [Membranoproliferative glomerulonephritis](https://durgical.com/en/conditions/membranoproliferative-glomerulonephritis/)

## Microorganisms 1

- [Hepatitis C virus](https://durgical.com/en/microbiology/hepatitis-c-virus/)

[← All of general pathology](https://durgical.com/en/general-pathology/)

Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Vasculitis| Angiitis | MedlinePlus](https://medlineplus.gov/vasculitis.html) (MedlinePlus, US National Library of Medicine, 2025).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/general-pathology/immune-complex-small-vessel-vasculitis/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/immune-complex-small-vessel-vasculitis/