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# Cutaneous small-vessel (leukocytoclastic, hypersensitivity) vasculitis

Inflammation of the tiny blood vessels of the skin, often after a drug or infection, that causes raised purple spots on the lower legs.

Updated 2026-11-01

## Structures involved

Tap one to see what it is and open it in 3D.

- [Skin](https://durgical.com/en/anatomy/skin/)
- [Leg veins](https://durgical.com/en/anatomy/anterior-tibial-veins/)
- [Great saphenous vein](https://durgical.com/en/anatomy/great-saphenous-vein/)
- [Anterior tibial artery](https://durgical.com/en/anatomy/anterior-tibial-artery/)
- [Kidneys](https://durgical.com/en/anatomy/kidney/)

## Why it happens

- [When leukocytes injure tissue: proteases, oxidants and NETs](https://durgical.com/en/general-pathology/when-leukocytes-injure-tissue-proteases-oxidants-and-nets/)
- [Hemorrhage: petechiae, purpura, ecchymosis, hematoma, and what blood loss does](https://durgical.com/en/general-pathology/hemorrhage-petechiae-purpura-ecchymosis-hematoma-and-what-blood-loss-does/)
- [Blood vessels: artery, vein and capillary layers](https://durgical.com/en/histology/blood-vessels-artery-vein-and-capillary-layers/)

## What it is

Inflammation limited to the small vessels of the skin (mostly post-capillary venules) that presents as palpable purpura, usually on the lower legs. It is also called leukocytoclastic or hypersensitivity vasculitis, and in the current nomenclature single-organ cutaneous small-vessel vasculitis. The key steps are to find the trigger and to make sure the vasculitis is not part of a systemic disease. IgA vasculitis is the IgA-mediated form and has its own page.

## Who gets it

One of the most common forms of vasculitis, with an estimated incidence of about 15 to 40 cases per million adults per year; it affects both sexes and all ages. In Colombia and Latin America the common triggers are drugs (especially antibiotics and anti-inflammatories) and infections such as streptococcal infection, viral hepatitis, HIV and dengue. No cause is found in a large share of cases.

## Causes

- Drugs, usually 7 to 10 days after starting them: beta-lactam antibiotics, sulfonamides, allopurinol, thiazides, phenytoin, anticoagulants and NSAIDs
- Infections: streptococcal infection, hepatitis B and C, HIV, infective endocarditis, dengue
- Connective tissue diseases: systemic lupus erythematosus, rheumatoid arthritis, Sjögren disease
- Cancer, mostly haematological (fewer than 5% of cases)
- Idiopathic in many patients

## Risk factors

- Recent new medication, especially antibiotics
- Recent infection
- Underlying autoimmune disease
- Prolonged standing, which favours lesions on the legs
- Chronic hepatitis C (cryoglobulins)

## Pathophysiology

A type III hypersensitivity reaction: circulating immune complexes formed against a drug or microbial antigen deposit in the walls of post-capillary venules, activate complement and attract neutrophils. The neutrophils damage the vessel wall and break apart (leukocytoclasis, seen as nuclear dust), causing fibrinoid necrosis and leakage of red cells into the dermis. That leakage with inflammation is what makes the purpura palpable. Gravity and slow venous flow explain why the lower legs are affected first.

## Classification

- By cause: drug-induced, infection-associated, connective tissue disease–associated, paraneoplastic or idiopathic
- Single-organ (skin-limited) vasculitis versus skin involvement of a systemic vasculitis
- Clinical variants: urticarial vasculitis (normo- or hypocomplementaemic) and IgA-dominant disease (IgA vasculitis)
- Acute self-limited versus chronic or relapsing disease

## Symptoms and signs

- Palpable purpura: raised red-purple spots that do not blanch with pressure, in crops on the lower legs and ankles
- Petechiae, small bruises, or blisters filled with blood
- Burning, itching or pain of the lesions
- Ankle swelling
- Joint aches, low-grade fever or malaise
- Wheals lasting more than 24 hours that leave bruising (urticarial vasculitis)

## Red flags

- Blood or protein in the urine, or rising creatinine (kidney involvement)
- Abdominal pain or blood in the stools (gut vasculitis)
- Haemoptysis or breathlessness (pulmonary haemorrhage)
- Numbness or foot drop (mononeuritis multiplex)
- Purpura with fever and shock, which can be meningococcaemia and needs emergency treatment
- Necrosis or deep ulcers of the skin

## Diagnosis

**Clinical**
The pattern of palpable, non-blanching purpura on the legs is typical. The history looks for new drugs in the previous weeks, infections and symptoms of connective tissue disease, and the examination looks for signs that other organs are involved.

**Tests**
[Skin](https://durgical.com/en/anatomy/skin/) punch biopsy of a fresh lesion (24 to 48 hours old) shows leukocytoclastic vasculitis; direct immunofluorescence on a lesion under 24 hours old looks for IgA (IgA vasculitis), IgM or complement. Urinalysis, blood count with platelets (normal platelets separate it from thrombocytopenic purpura), creatinine and [liver](https://durgical.com/en/anatomy/liver/) tests in every patient. As guided by the case: ANA, rheumatoid factor, complement, cryoglobulins, ANCA, hepatitis B and C and HIV serology, anti-streptolysin O, protein electrophoresis.

**Imaging**
Not needed for skin-limited disease. [Chest](https://durgical.com/en/anatomy/region/chest/) X-ray if there are respiratory symptoms; echocardiography if endocarditis is suspected.

## Differential diagnosis

- Thrombocytopenic purpura (immune thrombocytopenia), which is flat
- Meningococcaemia and other septic emboli
- IgA vasculitis, cryoglobulinaemic vasculitis and ANCA-associated vasculitis
- Pigmented purpuric dermatoses and stasis dermatitis
- Urticaria (wheals last less than 24 hours and leave no bruise)
- Drug eruptions without vasculitis

## Goal of treatment

Remove the cause, relieve symptoms while the rash settles, recognise systemic involvement early and treat chronic or ulcerating disease without unnecessary immunosuppression.

## Treatment

**Conservative**
Find and remove the trigger: stop the suspected drug and treat any underlying infection or disease; this alone usually clears the rash in a few weeks.

**Conservative**
Supportive care: rest with leg elevation, compression stockings once lesions stop being painful, analgesics or NSAIDs (if not the trigger), antihistamines for itch, and wound care for blisters or ulcers.

**Medical**
Chronic, recurrent or ulcerating disease: colchicine or dapsone; a short course of systemic glucocorticoids for severe disease; other immunosuppressants only for refractory cases or when a systemic vasculitis is present.

**Follow-up**
Monitoring: repeat urinalysis and blood pressure for several weeks to detect [kidney](https://durgical.com/en/anatomy/kidney/) involvement, and skin checks for infection of ulcers.

## Complications

- Skin ulcers, secondary infection and scarring
- Post-inflammatory brown pigmentation of the legs
- Chronic or relapsing course in a minority
- Missed systemic vasculitis with kidney damage

## Prognosis

Usually benign: most episodes resolve within a few weeks once the trigger is removed. About one in ten patients has chronic or recurrent disease. Outcome depends on whether a systemic vasculitis or serious underlying disease is present.

## Test yourself

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

## What is the typical skin lesion of small-vessel vasculitis and where does it appear?

Palpable, non-blanching purpura, mostly on the lower legs.

## What does the biopsy show?

Leukocytoclastic vasculitis: neutrophils around post-capillary venules with nuclear dust, fibrinoid necrosis and red cell extravasation.

## Which test must be done in every patient to detect systemic involvement?

Urinalysis (with creatinine), looking for haematuria, proteinuria or casts.

## How long after starting a drug does drug-induced vasculitis usually appear?

About 7 to 10 days.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/conditions/cutaneous-small-vessel-vasculitis/)

## Related conditions

- [IgA vasculitis (Henoch–Schönlein purpura)](https://durgical.com/en/conditions/iga-vasculitis/)
- [Cryoglobulinemic vasculitis](https://durgical.com/en/conditions/cryoglobulinemic-vasculitis/)
- [Granulomatosis with polyangiitis](https://durgical.com/en/conditions/granulomatosis-with-polyangiitis/)
- [Microscopic polyangiitis](https://durgical.com/en/conditions/microscopic-polyangiitis/)
- [Polyarteritis nodosa](https://durgical.com/en/conditions/polyarteritis-nodosa/)
- [Systemic lupus erythematosus](https://durgical.com/en/conditions/systemic-lupus-erythematosus/)
- [Rheumatoid arthritis](https://durgical.com/en/conditions/rheumatoid-arthritis/)
- [Sjögren disease](https://durgical.com/en/conditions/sjogren-disease/)
- [Viral hepatitis](https://durgical.com/en/conditions/viral-hepatitis/)
- [HIV infection and AIDS](https://durgical.com/en/conditions/hiv-infection-and-aids/)
- [Infective endocarditis](https://durgical.com/en/conditions/infective-endocarditis/)
- [Streptococcal pharyngitis](https://durgical.com/en/conditions/streptococcal-pharyngitis/)
- [Dengue](https://durgical.com/en/conditions/dengue/)
- [Immune thrombocytopenia (ITP)](https://durgical.com/en/conditions/immune-thrombocytopenia/)
- [Meningococcal disease (meningococcemia)](https://durgical.com/en/conditions/meningococcal-disease/)
- [Urticaria and angioedema](https://durgical.com/en/conditions/urticaria-and-angioedema/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Cutaneous small vessel vasculitis](https://dermnetnz.org/topics/cutaneous-small-vessel-vasculitis) (DermNet, 2026).

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