# Palpable Purpura: Workup

> Palpable purpura workup for NEET-PG Dermatology: leukocytoclastic vasculitis causes, biopsy timing, ANCA, cryoglobulins and IgA vasculitis.

- Canonical URL: https://prepelephant.com/topics/neet-pg/dermatology/palpable-purpura-workup
- Exam / course: NEET-PG · Subject: Dermatology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Palpable Purpura: Workup", PrepElephant, https://prepelephant.com/topics/neet-pg/dermatology/palpable-purpura-workup

## Direct answer

Palpable purpura means inflamed vessels, not failed platelets — a small-vessel leukocytoclastic vasculitis you can feel with a fingertip, demanding a cause-hunt rather than a haematinic prescription. The search sweeps five shelves: drugs (antibiotics, NSAIDs, diuretics), infections (streptococcal, hepatitis B and C, endocarditis, meningococcaemia), connective tissue disease (lupus, rheumatoid arthritis), ANCA-associated vasculitides (granulomatosis with polyangiitis, microscopic polyangiitis) and immune-complex syndromes such as IgA vasculitis and cryoglobulinaemia. Biopsy is the pivot — histology from a 24-48 hour lesion for neutrophils, fibrinoid necrosis and nuclear dust, direct immunofluorescence from a lesion under 24 hours where IgA deposition defines Henoch-Schonlein purpura — alongside urinalysis, ANCA, complement and hepatitis serology.

## What you must remember

- **Definition logic:** non-blanching, raised purple lesions = vessel-centred inflammation; flat purpura with normal vessels points instead to thrombocytopenia, senile purpura or coagulopathy — the first fork in every question.
- **Biopsy timing (the pearl):** histology from a 24-48 hour lesion for leukocytoclasia, fibrinoid necrosis and red-cell extravasation; direct immunofluorescence from a lesion under 24 hours — older lesions lose their immunoglobulin and waste the test.
- **IgA vasculitis (Henoch-Schonlein):** paediatric-age palpable purpura on buttocks and extensor legs plus arthritis, abdominal pain and nephritis; IgA-dominant deposits on DIF; ASO and streptococcal serology where relevant.
- **Core bloods:** full blood count, ESR, CRP, urinalysis for protein and blood, renal and liver function — urinalysis being the cheapest renal-vasculitis detector on the list.
- **Immunology set:** ANA, C3 and C4 (low in cryoglobulinaemia and lupus), ANCA with PR3 and MPO antibodies, cryoglobulins sent warm, rheumatoid factor (often positive with mixed cryoglobulinaemia).
- **Infection set:** hepatitis B surface antigen, anti-HCV, blood cultures if febrile, ASO titre or anti-DNase B in the post-pharyngitis child.
- **Retiform variant:** geometric, branch-like purpura signals thrombotic or embolic occlusion — warfarin necrosis, DIC, cryoglobulinaemia, cholesterol emboli — with biopsy showing bland thrombi rather than neutrophils.
- **Indian angles:** dengue and other thrombocytopenic fevers give flat purpura (a favourite trap); erythema nodosum leprosum gives tender nodules on shins that mimic vasculitis; tuberculosis and post-streptococcal states pepper the cause lists.

## Working through a case from lesion to label

A 34-year-old man arrives with crops of tender purple papules on both shins and ankles over ten days, some blistering, after a sore throat two weeks prior; he takes no regular drugs. Step one: confirm the lesion is palpable and non-blanching — vasculitis, not a platelet problem — though a baseline platelet count still belongs in the panel. Step two: biopsy pair — punch from a 36-hour lesion for histology, and a fresh 12-hour lesion snap-frozen for DIF. Step three: the panel — urinalysis traces blood (kidney involvement, the finding that changes prognosis), ANCA negative, complements normal, ANA negative, ASO raised, hepatitis serology negative. The constellation — post-streptococcal palpable purpura, arthralgia, microscopic haematuria, DIF showing IgA deposition — completes IgA vasculitis. Management is supportive with NSAIDs for joints, close blood-pressure and urinalysis surveillance, and nephrology referral because renal involvement decides long-term outcome. Had ANCA returned positive with cavitating lung lesions, the same legs would have redirected the patient to granulomatosis with polyangiitis and cyclophosphamide — identical skin, different life.

## Where candidates slip

The first slip is panel-only thinking: diagnosing "vasculitis" by bloods without biopsying, then being unable to answer the DIF question — IgA deposits define IgA vasculitis, and the specimen must be fresh, because immunoglobulin degrades in lesions older than a day. The second is forgetting that the urinalysis is part of the skin workup: finding nephritis upgrades disposition and prognosis regardless of the cause. The third is the retiform trap — geometric purpura is thrombotic (warfarin necrosis, DIC, cholesterol emboli), and treating it as inflammation misses a haematological or vascular emergency. Finally, in Indian wards, the febrile child with purpura is as often dengue with thrombocytopenia — flat, non-palpable lesions — as genuine vasculitis; palpability is the discriminator you are being tested on.

## Frequently asked questions

### What does palpability of purpura signify?
Inflammation of vessel walls with cellular infiltrate raising the lesion, indicating vasculitis rather than platelet or coagulation-failure bleeding.

### Why must the immunofluorescence biopsy come from a fresh lesion?
Immunoglobulin and complement degrade within about 24 hours, so an older lesion yields false-negative results in IgA vasculitis and immune-complex disease.

### Which investigations screen for renal vasculitis?
Urinalysis for protein and blood, serum creatinine, and blood pressure measurement — simple tests that detect the complication that matters most.

### What does a retiform pattern of purpura suggest?
Thrombotic or embolic occlusion — warfarin necrosis, DIC, cryoglobulinaemia or cholesterol emboli — with bland thrombi rather than neutrophilic vasculitis on histology.

### Which infection serologies belong in the palpable purpura panel?
Hepatitis B surface antigen, anti-HCV, ASO or anti-DNase B for streptococcus, and blood cultures when endocarditis or meningococcaemia are plausible.