Vasculitis Rash: Characteristic Features
Vasculitic rash most characteristically presents as palpable purpura—non-blanchable, raised purpuric lesions that are typically painful or burning, predominantly affecting the lower extremities. This is the hallmark cutaneous manifestation across vasculitis types 1, 2.
Primary Morphologic Features
The skin manifestations of vasculitis vary by vessel size and type:
Small-Vessel Vasculitis (Most Common Cutaneous Presentation)
Palpable purpura is the defining feature, occurring in approximately 15% of all ANCA-associated vasculitis (AAV) patients 1. The lesions are:
- Non-blanchable (do not disappear with pressure)
- Raised/palpable (distinguishing them from simple purpura)
- Painful or burning rather than pruritic 2
- Symmetrically distributed, predominantly on lower extremities and dependent areas 3, 4
Additional Cutaneous Manifestations by Vasculitis Type
In ANCA-Associated Vasculitis (GPA, MPA, EGPA):
- Petechiae/purpura (most frequent—15% overall) 1
- Skin involvement occurs in 28-47% depending on subtype 1
- In EGPA specifically: allergic manifestations including pruritus, urticaria, and maculopapular rash are more common than in other AAV subtypes 1
In Medium-Vessel Vasculitis (Polyarteritis Nodosa):
- Subcutaneous nodules 5
- Livedo reticularis (net-like vascular pattern) 5
- These reflect deeper vessel involvement
Less Common but Important Patterns
- Retiform or stellate purpura with central necrosis (particularly in levamisole-induced vasculitis) 6
- Bullae, papules, plaques 2
- Ulcers and digital gangrene (indicating deep dermal or subcutaneous muscular-vessel involvement) 3
- Livedo racemosa 3
Distribution Pattern
Lower extremities are preferentially affected due to:
- Hydrostatic pressure in dependent areas
- Gravity-dependent blood pooling
- This explains why leg elevation often provides symptomatic relief 3
Other commonly affected sites include trunk, extremities, and in certain vasculitides (like levamisole-induced), the nasal tip, digits, cheeks, and ears 6.
Critical Clinical Pitfall
The presence of cutaneous vasculitis, particularly palpable purpura, signals potential systemic involvement. Patients with skin lesions more frequently have severe systemic manifestations including alveolar hemorrhage and glomerulonephritis, especially in GPA, EGPA, and cytoplasmic/anti-PR3 ANCA-positive patients 1. The skin examination has both diagnostic and prognostic importance—it is not merely a cosmetic concern.
Diagnostic Confirmation
Skin biopsy is underutilized but highly effective 1:
- Performed in only 22-44% of patients with cutaneous manifestations
- Diagnostic in 68-94% when performed 1
- Should extend to subcutis from the most tender, reddish, or purpuric lesional skin 3
- Histology shows leukocytoclastic vasculitis with neutrophilic infiltration, fibrinoid necrosis, and nuclear debris 2, 3
Direct immunofluorescence helps distinguish IgA-associated vasculitis (Henoch-Schönlein purpura) from IgG/IgM-associated vasculitis, which has prognostic significance 3.
Temporal Evolution
The rash in vasculitis: