Cutaneous small-vessel vasculitis

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Cutaneous small-vessel vasculitis, often called cutaneous leukocytoclastic vasculitis, describes inflammation centred on post-capillary venules. Neutrophilic vessel injury allows erythrocytes and fluid into the dermis, producing raised non-blanching papules. Gravity and venous hypertension concentrate lesions around ankles and lower legs, but buttocks, thighs, arms and trunk can be involved. Lesions arrive in crops, evolve from erythematous or urticarial macules to purple-brown papules, and leave haemosiderin or post-inflammatory pigment as they flatten. On darker skin, palpation, oedema and a new grey, violet or brown hue may be more revealing than bright redness.

The dermatologist's task is to turn morphology and time into usable tissue. An old black ulcer mainly shows secondary necrosis; a new intact papule retains vessel-wall inflammation for routine histology. Immune deposits fade faster, so a separate earliest suitable lesion is selected for DIF and sent unfixed in the receiving laboratory's system. Depth must include the vessel calibre suspected. Photographs, exact site and lesion age, treatment exposure and clinical differential travel with the request because a pattern without context cannot establish cause.

Skin-restricted disease is diagnosed over time, not declared from one reassuring urine dip. Infection, medicine exposure and systemic symptoms are reviewed at baseline, and blood pressure, urine and renal function are repeated while new crops can still appear. Most single mild episodes resolve with cause control and supportive measures. Recurrent or destructive disease requires re-biopsy or diagnostic review, management of oedema and wounds, and selected anti-inflammatory therapy, while any organ involvement transfers treatment to the relevant systemic vasculitis pathway.

Key points

Cutaneous small-vessel vasculitis is a clinicopathological pattern of inflamed superficial dermal vessels, most often presenting as symmetrical palpable purpura on dependent legs.
Describe crops, age, elevation, blistering, pustules, ulcers and residual pigment; confluent angular necrosis suggests an occlusive vasculopathy or deeper-vessel process instead.
A dermatology assessment links each visible lesion to the sample required: a newly developed intact papule for full-depth H&E and a separate very early lesion for direct immunofluorescence.
Histological leukocytoclasis confirms damaged small vessels but cannot by itself identify medicine, infection, IgA, connective-tissue, clonal or idiopathic causation.
At presentation measure blood pressure and obtain urine, FBC, renal and liver profiles and inflammatory markers; organ symptoms or recurrent disease justify a broader directed screen.
Review every medicine and intermittent exposure against the eruption date, but do not stop an essential treatment without agreeing an alternative and recording the suspected reaction precisely.
First-line care for a mild skin-restricted episode is removal or treatment of the driver, temporary reduction in dependency, elevation, emollient, non-adherent dressings and safe analgesia.
Compression may help hydrostatic recurrence only after arterial sufficiency and acute inflammation are assessed; antibiotics are for clinical infection, not a positive swab from a colonised ulcer.
Repeated, painful or ulcerative crops need dermatology-led steroid-sparing treatment; systemic immune therapy belongs to severe skin disease or a defined organ vasculitis pathway.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Transient infection response

Upper-respiratory, streptococcal and other infections can trigger short-lived immune complexes, while persistent endovascular or viral infection can sustain vessel injury.

Medicine hypersensitivity

Antibiotics, NSAIDs, diuretics and numerous intermittent or prescribed medicines can precede crops by days or weeks, making exact exposure dates more useful than class lists.

Systemic inflammatory association

IgA vasculitis, connective-tissue disease, inflammatory bowel disease and systemic vasculitis may present first through superficial skin vessels before other organs declare themselves.

Clonal or unidentified driver

Paraprotein, haematological disease and occasionally solid malignancy underlie persistent presentations, although many isolated self-limited episodes remain idiopathic after proportionate investigation.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Complexes settle in venules
Circulating immune material deposits around superficial post-capillary venules, activates complement and generates chemotactic signals that recruit neutrophils.
2
Neutrophils damage walls
Activated cells release enzymes and fragment into nuclear debris, creating fibrinoid wall injury and the leukocytoclastic appearance on routine histology.
3
Vessels leak blood and fluid
Loss of endothelial integrity permits erythrocytes and plasma to enter dermis, producing non-blanching colour, palpable oedema, vesiculation and sometimes haemorrhagic bullae.
4
Gravity magnifies deposition
Slower dependent flow and higher lower-leg hydrostatic pressure encourage local leakage and help explain ankle clustering, oedema and recurrent crops after prolonged standing.
5
Healing leaves haemosiderin
Macrophages clear extravasated erythrocytes and store iron pigment, so flat brown or purple remnants may persist long after active vessel inflammation subsides.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Dependent palpable crops

Clusters of raised non-blanching papules around ankles and shins, often appearing in successive waves, are the core superficial-vessel morphology.

Early inflammatory macules

Fresh lesions may begin erythematous, urticarial or partly blanchable before erythrocyte leakage makes them fully purpuric and palpable.

Haemorrhagic blistering

Vesicles or tense blood-filled bullae over purpura indicate greater tissue injury and increase need for prompt biopsy, wound care and specialist review.

Ulcerated vasculitis

Painful shallow ulcers can follow confluent inflamed papules, while deep punched-out or retiform wounds should prompt reconsideration of vessel depth and occlusion.

IgA-associated phenotype

Purpura with ankle arthritis, colicky abdominal pain, gastrointestinal bleeding or renal abnormalities raises IgA vasculitis and demands structured organ follow-up.

Systemic vessel signalRed flag

Haemoptysis, renal decline, bowel ischaemia or bleeding, mononeuritis, fever and weight loss indicate disease beyond cutaneous venules.

Occlusion warningRed flag

Cold intensely painful skin, broken livedoid networks and angular black infarction are discordant with uncomplicated superficial leukocytoclastic disease.

Red flags requiring action

Toxic illness, rapidly advancing purpura, severe pain, necrosis, haemorrhagic bullae, proteinuria or haematuria, rising creatinine, haemoptysis, breathlessness, abdominal bleeding, focal weakness or constitutional loss demands expedited systemic investigation.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
H&E punch from a new papuleFirst step
Why
Confirm inflammatory small-vessel damage and assess depth and competing pathology.
Interpretation and limitations
Choose a fresh intact non-necrotic papule, generally within one to two days of appearing, and sample deeply enough; neutrophils, nuclear dust, fibrinoid change and red-cell leakage support the pattern.
02
Separate early-lesion DIF
Why
Characterise immunoglobulin and complement deposited around vessels before the signal degrades.
Interpretation and limitations
Use the newest suitable erythematous or purpuric lesion, often under twenty-four hours old, in laboratory-specified medium; negative aged or treated tissue has limited exclusion value.
03
Blood pressure, urine and renal profile
Why
Detect glomerular disease that may be clinically silent when the skin eruption begins.
Interpretation and limitations
Confirm persistent blood or protein with microscopy and quantification; hypertension, casts or deteriorating filtration needs urgent renal and systemic-vasculitis assessment.
04
FBC, film, CRP, liver and coagulation
Why
Assess inflammation and expose cytopenic, infectious, hepatic, haematological and bleeding mimics.
Interpretation and limitations
Thrombocytopenia or abnormal coagulation can explain flat purpura without vasculitis; eosinophilia supports but does not prove a drug-related process.
05
Cause-directed immune and protein tests
Why
Investigate persistent, recurrent, severe or organ-associated disease without indiscriminate screening.
Interpretation and limitations
Select ANA, complement, ANCA, immunoglobulins, electrophoresis, immunofixation and cryoglobulins from phenotype; keep cryoglobulin samples warm until serum separation and interpret antibodies clinically.
06
Infection assessment
Why
Identify a treatable trigger and avoid dangerous immune suppression of occult infection.
Interpretation and limitations
Use throat, blood or tissue cultures, hepatitis and HIV testing, echocardiography or other studies from exposure and systemic clues; biopsy organisms when infection remains in the ulcer differential.
07
Ulcer and vascular assessment
Why
Define perfusion, depth, oedema, infection and a safe dressing or compression plan.
Interpretation and limitations
Document wound dimensions, border, base, exudate, pulses and ABPI or toe pressure when indicated; swab only clinically infected wounds and image suspected deep infection.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Platelet or clotting disorder

Flat petechiae, mucosal bleeding, thrombocytopenia or abnormal coagulation indicate haemostatic failure without the raised inflammatory papules and vessel-wall histology.

Occlusive vasculopathy

Antiphospholipid disease, emboli, livedoid vasculopathy and calciphylaxis create painful retiform infarction through blocked lumina rather than primary venular inflammation.

Pigmented purpuric dermatosis

Longstanding cayenne-pepper macules and patches with little elevation, pain or systemic illness reflect capillaritis and haemosiderin leakage without destructive vasculitis.

Medium-vessel vasculitis

Tender subcutaneous nodules, livedo, deep irregular ulcers and mononeuritis suggest muscular-vessel involvement that needs a deeper biopsy and systemic assessment.

Infection or neutrophilic ulcer

Ecthyma, endocarditis emboli and pyoderma gangrenosum can be purpuric or ulcerative, so cultures, border morphology and pathergy context prevent unsafe immune treatment or debridement.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01First-line dermatology sequencePhotograph, time and pair the samplesFirst stepFirst lineNew palpable purpura is stable enough for an outpatient or ward diagnostic pathway.

1Map lesion crops and organ symptoms, record blood pressure and urine and photograph representative early, established and ulcerated lesions with consent.
2Select one recent intact raised papule for formalin histology and a separate freshest appropriate lesion for DIF, confirming medium and courier timing with the laboratory.
3Submit exact lesion ages, sites, medicines, prior corticosteroid, systemic findings and differential and review pathology beside the evolving photographs rather than in isolation.

02First-line skin-limited careControl dependency and protect the barrierFirst lineInitial testing is reassuring, lesions are non-necrotic and no organ syndrome is present.

1Treat a confirmed infection or other driver and agree safe withdrawal or substitution of a plausible new medicine with its prescriber.
2During painful crops use leg elevation, reduced prolonged standing, emollient, non-adherent absorbent dressings and analgesia that respects renal, gastrointestinal and bleeding risk.
3Assess arterial circulation and inflammation before graduated compression, then review new-lesion count, wounds, urine and renal function rather than promising immediate permanent resolution.

03Persistent cutaneous routeUse a bounded steroid-sparing trialNew crops continue, recur or ulcerate after trigger control and supportive management.

1Revisit histology, infection, venous hypertension, medicine dates and systemic features and consider deeper repeat tissue if morphology has become nodular or retiform.
2With dermatology, offer an off-label colchicine or dapsone trial selected by renal, hepatic, interaction, G6PD, blood and reproductive context and set a documented response interval.
3Reserve a short systemic glucocorticoid course for severe painful bullous or ulcerative inflammation after infection review and establish a longer-term diagnosis-specific plan before repeated exposure.

04Organ escalationRetire the skin-limited labelEscalationRenal, pulmonary, bowel, neurological or constitutional abnormalities emerge during any phase.

1Admit or arrange urgent specialty assessment according to severity and repeat urine, renal function, blood count, inflammatory markers and organ-directed imaging or tissue tests.
2Exclude sepsis, endocarditis, viral infection, thrombotic microangiopathy and occlusive vasculopathy in parallel where phenotype overlaps.
3Begin disease-specific systemic treatment through the responsible multidisciplinary team while continuing wound, pain and pressure management for the skin.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

May reduce painful recurrent skin crops after trigger removal and dependency care when disease remains confined to skin, although the evidence base is limited.

Colchicine specialist trial

Use 500 micrograms by mouth once daily initially and, if required and tolerated, increase to 500 micrograms twice daily for a defined off-label trial with an agreed stop date.

Avoid or reduce in significant renal or hepatic impairment and stop for diarrhoea, vomiting, cytopenia or muscle symptoms. Macrolides, azoles, ciclosporin, verapamil and some statins can cause fatal accumulation; pregnancy and breastfeeding need specialist review.

An off-label neutrophil-modulating option for recurrent or ulcerative cutaneous disease when colchicine is unsuitable or ineffective.

Dapsone specialist alternative

A dermatologist may begin 50 mg by mouth once daily and increase to 100 mg once daily only after baseline safety tests and early blood monitoring confirm tolerability.

Check G6PD activity, FBC, reticulocytes, liver and renal function first. Haemolysis and methaemoglobinaemia can occur with normal G6PD; fever, mouth ulcer, bruising, cyanosis, dyspnoea, jaundice, neuropathy or severe rash needs urgent cessation and assessment.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Painful ulceration

Confluent vessel injury can destroy epidermis and dermis, causing exudative wounds, secondary infection, slow healing, scar and persistent pigment alteration.

Kidney or bowel injury

An IgA or other systemic phenotype can produce glomerulonephritis, gastrointestinal bleeding, intussusception or bowel ischaemia after the cutaneous eruption begins.

Pulmonary or nerve damage

Systemic small- or medium-vessel inflammation may cause alveolar haemorrhage or mononeuritis, leaving respiratory failure or permanent motor and sensory deficit.

Recurrent dependent disease

Ongoing venous hypertension, repeated exposure or an untreated inflammatory driver produces repeated crops, chronic oedema and functional lower-leg pain.

Treatment-related harm

Glucocorticoid, colchicine and dapsone can cause infection, metabolic disease, marrow suppression, haemolysis, methaemoglobinaemia, drug accumulation and neuromuscular toxicity.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Count genuinely new lesions and record pain, palpability, blistering, ulcer dimensions and residual pigment using consistent photographs rather than treating all purple marks as active disease.
Repeat blood pressure, urinalysis and renal function during the active period and after an IgA phenotype because organ involvement can follow skin onset.
At each review ask directly about breathlessness, haemoptysis, abdominal pain, gastrointestinal bleeding, weakness, numbness, fever and weight loss.
For wounds, monitor perfusion, exudate, edge progression and cellulitis and avoid routine repeated swabs from clinically uninfected colonised surfaces.
During colchicine review bowel toxicity, kidney and liver function, blood count, interacting medicines and new proximal weakness or neuropathy.
During dapsone follow the specialist FBC and liver schedule and investigate falling haemoglobin, oxygen-saturation discrepancy, cyanosis or exertional symptoms promptly.
After resolution, document the most likely trigger and certainty, remove unnecessary broad allergy labels and give a route back for recurrent crops or organ symptoms.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

The lesions form a timeline

An erythematous macule, raised purpuric papule and pigmented flat remnant can coexist, showing successive stages rather than three separate diagnoses.

DIF ages quickly

Immune deposits can disappear before vessel-wall destruction, so the best fluorescence site is usually younger than the best routine-histology papule.

Histology names injury

Leukocytoclasis describes neutrophil-fragmenting vessel damage and still leaves the clinician responsible for finding cause, distribution and organ extent.

Ulcer shape challenges depth

A deep punched-out or geometric infarct is a cue to sample more deeply and reconsider medium-vessel inflammation, thrombosis, pressure and pyoderma gangrenosum.

Dependency is a cofactor

Hydrostatic pressure helps explain lower-leg clustering and recurrence, so elevation and carefully selected compression can complement immune and causal treatment.

Skin-limited requires surveillance

The absence of organ signs on day one is reassuring but provisional; repeated urine and symptom review establish the eventual classification.

11Common pitfallsFrequent interpretation and management errors.

01
Using a months-old pigmented macule or necrotic ulcer centre for both H&E and DIF.
02
Sending the fluorescence specimen in formalin or without confirming the local transport deadline.
03
Calling leukocytoclastic histology a complete aetiological diagnosis and stopping the trigger and organ assessment.
04
Starting immunosuppression in febrile purpura before cultures and endovascular infection have been considered.
05
Applying high compression to an ulcerated leg without assessing arterial perfusion and acute inflammatory pain.
06
Using repeated antibiotics for colonisation or repeated prednisolone for every crop without reviewing morphology and cause.
07
Assuming residual brown-purple staining represents continuing vessel inflammation and escalating therapy on colour alone.