Solar Purpura is NOT Blanchable
Solar purpura (also called senile purpura or actinic purpura) is definitively non-blanchable because it represents extravasated red blood cells in the dermis from fragile, sun-damaged blood vessels—not active vascular dilatation.
Pathophysiology Explains the Clinical Finding
The key distinguishing feature of purpura is that it represents hemorrhage into the skin, not vascular congestion:
- Purpuric lesions are hemorrhagic by definition and do not blanch with pressure 1
- Solar purpura results from chronic photodamage causing dermal atrophy, collagen degradation, and loss of perivascular support, leading to vessel fragility and spontaneous rupture 2, 3
- The red-brown discoloration comes from extravasated erythrocytes and subsequent hemosiderin deposition in the dermis, not from dilated blood vessels 1
Clinical Presentation
Solar purpura typically manifests as:
- Non-blanchable purpuric patches on sun-exposed areas, particularly the dorsal forearms and hands of elderly patients with chronic sun damage 2
- Lesions appear after minor trauma in patients with fragile, atrophic skin (dermatoporosis) 3
- The purpura may have an orange-brown, speckled appearance as hemosiderin is deposited over time 1
Critical Diagnostic Pitfall
Do not confuse solar purpura with inflammatory vascular conditions:
- Unlike urticarial vasculitis or other inflammatory vasculitides, solar purpura is non-inflammatory and represents mechanical vessel rupture, not active vasculitis 1
- Solar capillaritis is a distinct entity that can cause acute purpura after UV exposure and shows capillaritis on histology, but the resulting purpura is still non-blanchable 4
- The blanch test is critical: apply firm pressure with a glass slide (diascopy)—if the lesion disappears, it's vascular congestion (blanchable); if it persists, it's purpura (non-blanchable) 1
Clinical Significance
Solar purpura serves as a visible marker of: