Purpura is classified according to the the underlying cause:
1- Platelet disorders (Thrombocytopaenic purpura): destruction of platelets and decreased platelet count, sometimes due to infection, drugs, or certain diseases, other times no cause is identified (idiopathic)
2- Vascular disorders (Non-thrombocytopaenic purpura) where red blood cells leak as a result of:
Damage to small blood vessels
Increase in the venous pressure
Deficient vascular support, as in aged or sun damaged skin (senile purpura)
3- Coagulation disorders: affecting the ability of the blood to clot properly.
The hallmark of a PPD is its characteristic orange-brown, speckled, cayenne pepper–like discoloration. A number of factors have been implicated in the appearance of PPD, and include venous hypertension (increased pressure in the veins), exercise and lower limbs dependence.
The capillaries are small blood vessels near to the skin surface. For unknown reasons they sometimes become inflamed, although a true vasculitis is not seen on skin biopsy. Blood cells leak out through small gaps that arise between the cells, which make up the capillary walls. The result is tiny red dots appear on the skin, described as cayenne pepper spots. They group together to form a flat red patch, which becomes brown and then slowly fades away over weeks to months.
The cause of capillaritis is usually unknown. Occasionally it arises as a reaction to a medication; many different drugs have been occasionally associated with capillaritis. In others a food additive or a viral infection may be responsible. Capillaritis may also develop after exercise.
There are three suggested underlying disease mechanisms to explain capillaritis:
- The first is due to the weakness or disturbance of the cutaneous (skin-related) blood vessels resulting in red blood cells leaking out of capillaries becoming fragile.
- Second is due to immune causes in the blood stream.
- The third mechanism is associated with the cellular immunity.
An entity known as Progressive Pigmentary Dermatosis may occur at any age but is more common among males. The average age of onset is amongst 40 years old patients. This condition has been linked with leaky blood vessel walls. The lower limbs are most commonly affected though other areas of the body may also be involved. Irregular plaques and patches of orange-brown pigmentation appear and spread slowly. The lesions are chronic and may persist for years but some may spontaneously clear. Associations include venous disease, food additive and food coloring hypersensitivity. These lesions are typically asymptomatic except for mild itchiness that happens occasionally. Symptoms may be controlled using topical steroids.
Other possible diagnoses which are variants of Pigmented purpuric dermatoses exist; in order to pin the correct diagnosis, a physical examination is required.
Additionally, evaluation of the platelet count (by doing a complete blood count) and clotting factors (if deemed necessary by the treating physician) will be required to rule out a bleeding disorder.
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