A group of disorders in which reddish-purple spots appear on the skin
In the conditions known as purpura, reddish-purple spots or bruise-like discolorations develop on the skin. The spots or bruises, called purpuric spots, result from small areas of bleeding under the skin and may be caused by damaged blood vessels or by an abnormality in the blood. The appearance of the spots varies, and they can range from the size of a pinhead to about 2.5 cm (1 in) in diameter. Unlike many other red rashes, purpuric spots do not fade when they are pressed.
The spots themselves are harmless, but purpura is sometimes a sign of a potentially serious underlying disorder.
The most common type of purpura is senile purpura, which occurs mainly in elderly people. The condition gives rise to dark bruises, typically on the backs of the hands and forearms and on the thighs. Senile purpura is due to weakening of the tissues that support the blood vessels under the skin; these weakened blood vessels become susceptible to damage and bleed easily.
Very small purpuric spots, known as petechiae, often result from a reduction in the number of platelets (cells in the body that help the blood to clot). Platelet deficiency can be associated with many bone marrow disorders, such as leukaemia, or with autoimmune disorders. The condition may also occur as a side effect of treatment with some drugs, such as diuretic drugs or antibiotics.
Purpuric spots of variable size may be a sign of a serious bacterial infection of the blood (see Septicaemia). In some people, the infection may be due to a type of bacterium called meningococcus, which can result in potentially life-threatening meningitis. If purpura appears in conjunction with a fever, you should seek emergency medical advice.
Henoch–Schönlein purpura is an uncommon type of purpura occurring in childhood and caused by inflammation of small blood vessels. The spots that appear in this condition are unlike those in other forms of purpura and resemble small, raised lumps.
Senile purpura is usually diagnosed from the bruise-like appearance of the spots. The condition is harmless, and no treatment is needed. The spots fade gradually but are likely to recur.
Any obvious underlying disorder, such as meningitis, will be treated. If the cause of the purpura is not obvious, your doctor may arrange for blood tests to find out if the platelet levels in the blood and the ability of the blood to clot are normal.
If blood tests show an abnormality, your doctor may refer you to a specialist for further investigations. If you are found to have a very low platelet count, you may be given platelet transfusions to prevent serious internal bleeding from occurring, especially in the brain, until the underlying disorder can be diagnosed and treated. The purpura should disappear once the cause has been successfully treated. If the condition is the result of an autoimmune disorder, your doctor may prescribe corticosteroid drugs (see Immunosuppressants) to clear it up.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.