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Author: Dr Leah Jones, Medical Registrar, Christchurch District Health Board, Christchurch, New Zealand. Copy edited by Gus Mitchell. November 2020.
Retiform purpura is a branching, non-blanching patch or plaque often with skin necrosis and ulceration due to skin ischaemia.
The demographic group affected depends on the underlying diagnosis. Adults and children can present with retiform purpura.
Retiform purpura results from either blood vessel wall damage or occlusion of the vessel lumen causing complete vessel obstruction and skin ischaemia downstream.
Retiform purpura due to calciphylaxis
Retiform purpura have been reported in seriously ill COVID-19 patients due to microthrombi.
Retiform purpura due to vessel lumen occlusion
Retiform purpura presents as painful dark red or purple patches or plaques with peripheral branching and central purpura, necrosis, and/or ulceration. They can vary in size from small (1–2 cm) to large (>10 cm), may be single or multiple, localised or disseminated. The branching, which is not the same as the netlike pattern of livedo, may only be seen at the edge of one or two lesions but is still the clue to this diagnosis and a potentially serious underlying condition.
Clinical clues to the underlying cause may include the following.
Retiform purpura of the lower limbs due to vessel wall damage
Retiform purpura is not well described in darker skin types. However, case reports note the purpura to be a dark purple colour, rather than the bright red that may be observed in lighter skin types.
Retiform purpura can be complicated by:
Complications depend on the underlying cause.
Retiform purpura is a clinical diagnosis based on the typical appearance. Investigations are required to determine the underlying cause and will be guided by:
Routine tests will include:
A skin biopsy taken from the peripheral purpuric rim should be performed; the histology varies with the underlying diagnosis. Examples include warfarin necrosis pathology, calciphylaxis pathology, and cholesterol emboli pathology.
The differential diagnosis of retiform purpura includes:
Ulcerated skin lesions may require appropriate wound dressings and debridement of necrotic tissue. Circulatory support and blood product replacement may be necessary.
Treatment of retiform purpura is the specific treatment of the underlying cause.
The outcome depends on the underlying diagnosis of the retiform purpura, ranging from removable precipitants such as emboli secondary to a procedure with full recovery expected, through to life-threatening situations as in a disseminated opportunistic infection.
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