What is Palpable Purpura?
Palpable purpura is a raised, non-blanching skin lesion that you can feel with your fingers, representing blood that has leaked from small blood vessels into the skin, most commonly caused by inflammation of the vessel walls (vasculitis). 1
Clinical Definition and Pathophysiology
Palpable purpura occurs when antigen-antibody complexes deposit along small cutaneous vessels (postcapillary venules), causing vessel wall inflammation and subsequent extravasation of red blood cells into the surrounding tissue 1. The key distinguishing feature is that these lesions are raised and palpable on examination, unlike simple purpura which is flat.
Diagnostic Significance
Palpable purpura is the hallmark clinical finding of cutaneous small-vessel vasculitis 2. When you encounter palpable purpura, you should immediately think of leukocytoclastic vasculitis as the most common underlying pathology 1, 3.
Diagnostic Performance
- When palpable purpura is present, it has an 82% sensitivity and 86% positive predictive value for leukocytoclastic vasculitis 3
- In one study, 86% of patients with palpable purpura had histologically confirmed vasculitis 3
Common Etiologies
The most frequent causes include:
- IgA vasculitis (Henoch-Schönlein purpura) - the most common cause in both children and adults, accounting for approximately 59% of cases 4
- Cutaneous leukocytoclastic vasculitis - approximately 24% of cases 4
- ANCA-associated vasculitis (GPA, MPA, EGPA) - less common but important to identify 5
- Drug-induced vasculitis - particularly sulfonamides, penicillins, and related compounds 6
- Infection-associated - including bacterial endocarditis, hepatitis B and C, and other infections 2, 7
- Rheumatologic disease-associated vasculitis - approximately 7% of cases 4
Clinical Context and Associated Features
In ANCA-Associated Vasculitis
Palpable purpura is specifically mentioned as a diagnostic feature in EGPA, where it represents the most vasculitis-specific skin lesion 5. In EGPA patients with palpable purpura, skin biopsy invariably reveals leukocytoclastic vasculitis 5.
Systemic Involvement
When palpable purpura occurs with other organ involvement (arthritis, abdominal pain, renal disease), consider:
- IgA vasculitis - characterized by the tetrad of palpable purpura, arthritis, abdominal pain, and glomerulonephritis 8
- Systemic vasculitis - requiring evaluation for kidney, gastrointestinal, and neurologic involvement 5
Key Clinical Pitfalls
Not all palpable purpura is vasculitis: While most cases (82-86%) represent true vasculitis, approximately 14-18% may show purpura without vessel wall inflammation on biopsy 3
Biopsy considerations: Although skin biopsy can confirm vasculitis, if the clinical presentation is typical, biopsy may not be essential 3. However, biopsy is recommended when feasible to confirm diagnosis and exclude differential diagnoses 5
Drug etiology: Always consider medication-induced vasculitis, particularly in cases limited to the skin without systemic involvement 6
Infectious endocarditis: In any febrile patient with palpable purpura and a cardiac murmur, blood cultures must be performed to exclude bacterial endocarditis 2, 7
Clinical Examination Technique
The defining characteristic is that you can feel the lesions - they are raised above the skin surface, distinguishing them from flat purpura or petechiae. The lesions are typically:
- Non-blanching (do not disappear with pressure)
- Symmetrically distributed
- Most commonly on dependent areas (lower extremities)
- May be accompanied by other skin findings (nodules, vesiculobullous lesions, ulcerations) 2