Capillaritis (Q44078)

Capillaritis results from extravasation of red blood cells from leaky capillaries into the dermis and manifests initially as a finely stippled pink to purple purpura, most commonly affecting the lower limbs. As iron is released and converted into haemosiderin, the skin stains gold or brown. Various patterns of capillaritis have been described and given separate names depending on the distribution, time course, extent and degree of pigmentation and presence or otherwise of epidermal thickening. The underlying processes involved in all these variants are very similar and of unknown cause. Histology may show mild inflammation around capillaries but no vasculitis.