Cutaneous small-vessel vasculitis
Also called leukocytoclastic vasculitis, palpable purpura, vasculitis
Inflammation destroying the small dermal vessels: purpura you can FEEL, dependent and symmetric, sometimes blistering or ulcerating. The skin finding is the easy half; the work is deciding what lit the fire (drug, infection, systemic vasculitis, malignancy) and whether internal organs are burning too.
How it looks
Symmetric palpable purpuric papules, some with central necrosis, densely distributed over the lower legs and ankles.
Rose is the lesion, grey the pattern the lesions make, green where on the body it lives.
Across skin tones
Purpura reads dark brown to black rather than red-purple in deeply pigmented skin and is easily missed early; palpability and the glass test do not depend on hue, which is why the finger matters more than the colour here.
Don't miss
Purpura plus fever in an unwell patient is the meningococcal-sepsis corner of this territory: culture, antibiotics, and escalation come before any vasculitis work-up.
Forms & variants
IgA vasculitis (Henoch-Schonlein purpura)
The childhood classic: palpable purpura over buttocks and legs plus abdominal pain, arthralgia, and nephritis; skin-wise self-limited, kidney-wise followed with urinalysis for months.
Granulomatosis with polyangiitis (GPA)
ANCA-associated vasculitis wearing skin signs: palpable purpura, ulcers, and necrotic papules alongside sinus, lung, and kidney disease; skin vasculitis plus ENT or renal symptoms sends ANCA, urgently.
Symptoms & course
- Burning or tenderness more than itch
- Crops appear over days, favouring dependent areas and pressure sites
- Systemic symptoms (fever, arthralgia, abdominal pain, haematuria) are the questions that matter
Diagnostic approach
- Confirm: biopsy within 24-48 hours of a fresh lesion, with direct immunofluorescence for IgA
- Cause: drug and infection history, cultures where indicated, ANCA, complement, cryoglobulins, hepatitis serology as directed
- Extent: urinalysis every time, the kidney is the silent organ
Differential, and how to separate them
- Morbilliform drug eruption
Favours it: A widespread red eruption after a new drug
Against it: Exanthems blanch and lie flat; vasculitic purpura is non-blanching and palpable
- Urticaria
Favours it: Red raised lesions on the legs
Against it: Wheals vanish within a day; a 'wheal' fixed beyond 24 hours that bruises as it fades is urticarial vasculitis, which is this family, not hives
- Cellulitis
Favours it: A red, tender lower leg
Against it: Cellulitis is one confluent unilateral field, not bilateral discrete purpuric papules
Management principles
- Treat or remove the trigger; many episodes are self-limited with rest, elevation, and support
- Colchicine or dapsone for persistent skin-limited disease
- Systemic involvement escalates to immunosuppression and the relevant specialty
Clinical pearl: Close your eyes and run a finger over the rash: purpura you can feel is vasculitis until proven otherwise, and a dipstick of urine is part of the skin examination.
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