Synopsis
Recognise palpable-purpuric small-vessel inflammation, separate skin-limited disease from systemic vasculitis and mimics, biopsy the correct lesions, remove triggers and escalate only persistent, ulcerating or organ-associated disease.
- The hallmark is palpable non-blanching purpura, usually in crops on dependent lower legs; vesicles, bullae, pustules, urticarial plaques, ulcers or necrosis can occur.
- Cutaneous small-vessel vasculitis describes a vessel pattern and distribution, not one cause; always decide whether disease is skin-limited, systemic or secondary to infection, medicine, autoimmunity or malignancy.
- At the first assessment check observations, blood pressure, urine dip, creatinine, FBC and symptoms from lungs, kidneys, bowel and nerves before calling the eruption benign.
- For diagnostic confirmation, ideally take two lesions less than 48 hours old: a non-necrotic purpuric papule for routine histology and an early partially blanchable macule for direct immunofluorescence.
- Routine histology showing leukocytoclasis proves small-vessel inflammation but not its cause; IgA, complement or immunoglobulin deposition and the clinical phenotype refine classification.
- A single mild skin-limited episode is usually managed first by removing a credible trigger, treating infection, rest, leg elevation, skin care, analgesia and compression only when arterial supply is adequate.
- Persistent, recurrent, painful, bullous or ulcerating disease needs dermatology review; colchicine or dapsone are specialist off-label steroid-sparing choices with different renal, interaction, G6PD and blood-monitoring constraints.
- Systemic glucocorticoid is reserved for severe skin disease or organ involvement after infection assessment; it is not routine treatment for every purpuric crop.
- Do not inject or immunosuppress a suspected infected lesion and do not use an NSAID when nephritis, gastrointestinal bleeding, significant renal disease or cardiovascular contraindication is present.
Key red flags
Breathlessness, haemoptysis, falling oxygen saturation or bilateral infiltrates raises diffuse alveolar haemorrhage or infection and requires acute admission.
Haematuria, proteinuria, rising creatinine, oedema or hypertension suggests glomerulonephritis and needs urgent renal and vasculitis assessment.
Severe abdominal pain, gastrointestinal bleeding or guarding may represent bowel vasculitis, ischaemia, perforation or another surgical emergency.
New focal weakness, foot drop, asymmetric sensory loss, confusion or seizure indicates possible peripheral or central nervous-system vasculitis.
Retiform purpura, bullae, ulceration, necrosis, rapidly progressive pain or cold poorly perfused tissue suggests occlusion, deeper-vessel disease or severe inflammation.
Fever, hypotension, non-blanching rash and toxicity require an immediate sepsis and meningococcal pathway, not a delayed dermatology work-up.
Haematuria, breathlessness, abdominal pain, bleeding, fever, weight loss or focal neuropathy accompanying purpura moves assessment beyond skin-limited disease.
Livedo, angulated retiform purpura, cold tissue or necrosis suggests thrombosis, embolism, cryoprotein or deeper-vessel disease rather than uncomplicated leukocytoclastic inflammation.
Investigation priorities
Identify sepsis, hypertension and silent glomerular involvement at the initial encounter.
Management branches
A new non-blanching palpable eruption is identified.
- Record observations and blood pressure, examine lesion morphology and perfusion and ask systematically about renal, pulmonary, bowel, neurological and infectious symptoms.
- Perform urine dip, FBC, renal and liver tests and inflammatory markers and arrange same-day escalation for toxicity, necrosis or any organ signal.
- Photograph active untreated lesions and secure appropriately timed routine-histology and DIF biopsies when confirmation will alter classification.
The patient is well, baseline organ assessment is reassuring and lesions are non-necrotic.
- Review and remove a credible medicine trigger safely, treat identified infection and avoid adding an unnecessary antibiotic or immunosuppressant.
- Use rest during painful crops, leg elevation, bland emollient, appropriate dressings and compression only after arterial adequacy is established.
- Offer symptom-specific analgesia, topical corticosteroid for inflammatory itch or antihistamine, then review urine and trajectory with clear return advice.