Cutaneous Small Vessel Vasculitis
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Direct answer
Cutaneous small vessel vasculitis is an immune complex inflammation of postcapillary venules that produces palpable purpura, most often on the lower legs. Its histological hallmark is leukocytoclastic vasculitis, with neutrophilic nuclear debris and fibrinoid necrosis in the small vessel wall. The essential task is hunting for the trigger, usually a drug or an infection, because removing it often clears the disease.
What you must remember
- Palpable purpura: raised purpura you can feel with a finger signals inflammation, whereas flat purpura points to thrombocytopenia or a coagulation defect.
- Site and spread: the lower limbs are typical, and severe cases progress to vesicles, bullae, ulceration or necrosis.
- Histology: leukocytoclasis, neutrophilic infiltrate and extravasated red cells in the venular wall; biopsy an early lesion, ideally under 48 hours old.
- Common triggers: drugs such as beta-lactam antibiotics, sulphonamides, NSAIDs and frusemide, plus infections, connective tissue disease and malignancy.
- Infection screen: hepatitis B and C serology, HIV testing and antistreptolysin O titre, since hepatitis B is common in India.
- Organ check: urinalysis, serum creatinine and an abdominal review decide whether the disease is confined to skin.
- Management: remove the trigger and support the patient, reserving systemic corticosteroids for severe disease and dapsone for persistent mild lesions.
A stepwise search for the trigger
A 45-year-old man develops palpable purpura on both ankles about a week after starting antibiotics for a urinary infection. Nothing else in his history stands out, but the lesions still need a full workup.
- Confirm the vasculitis: palpable purpura with leukocytoclastic histology confirms the diagnosis, whereas flat purpura with a normal biopsy suggests a non-inflammatory cause.
- Stop the suspect drug: list every medicine started in the preceding few weeks, including over-the-counter preparations, and withdraw the most likely culprit.
- Screen for infection: test for hepatitis B and C, HIV and recent streptococcal infection, since each can drive immune complex deposition.
- Check the kidneys and gut: urinalysis, creatinine and abdominal assessment show whether the disease is limited to skin or has become systemic.
- Look for connective tissue disease: antinuclear antibody, complement levels and cryoglobulins help identify lupus, Sjogren syndrome or a paraproteinaemia.
- Treat and follow: supportive care and leg elevation come first, with corticosteroids for severe disease and dapsone for persistent mild lesions.
Where the exam tries to catch you
Three traps recur, and each one mistakes vasculitis for a simpler condition.
- Trap: attributing palpable purpura to low platelets because the colour looks like bruising. Correct: platelet counts are normal in small vessel vasculitis, and palpability is the clue that points to inflammation.
- Trap: stopping at the drug history and skipping hepatitis serology. Correct: hepatitis-related cryoglobulinaemic vasculitis is a recognised cause, so serology belongs in every workup.
- Trap: treating renal or gut involvement with skin care alone. Correct: visceral involvement needs systemic evaluation and treatment, because topical care does not protect the kidney.
Frequently asked questions
Which histological feature defines cutaneous small vessel vasculitis?
Leukocytoclastic vasculitis defines the condition, showing neutrophilic infiltration, nuclear dust from fragmented neutrophils and fibrinoid necrosis of postcapillary venules. Direct immunofluorescence often shows immune complex deposits in the vessel walls, which supports the diagnosis.
Which investigations search for the cause of cutaneous small vessel vasculitis?
Hepatitis B and C serology, HIV testing, antistreptolysin O titre, antinuclear antibody, complement levels and cryoglobulins cover the commonest causes. A detailed drug history and urinalysis complete the screen, because cutaneous small vessel vasculitis is often drug-induced.
Why is an early skin biopsy important in cutaneous small vessel vasculitis?
A lesion under about 48 hours old shows the neutrophilic infiltrate and nuclear debris that define leukocytoclasis. Older lesions can show nonspecific changes, so cutaneous small vessel vasculitis is best confirmed on an early, palpable lesion.
When does cutaneous small vessel vasculitis need systemic treatment?
Mild, drug-triggered cutaneous small vessel vasculitis often settles once the trigger is removed, with symptomatic care alone. Ulceration, severe disease, or renal, gut or neurological involvement needs systemic corticosteroids and specialist review.