Purpura

Written by Dr Claire Harrison, lecturer in haematology and Professor Samuell Machin, professor of haematology

What is purpura?

Spontaneous bleeding into the skin usually appears as a rash known as purpura (Figure 1).

Petechiae is the term given to the individual small red or red-blue spots about 1 to 5mm in diameter which make up the rash. They are caused by a small local amount of bleeding within the skin. Deeper bleeding beneath the skin may be seen as bruises (ecchymoses).

The difference between petechiae and abnormally prominent blood vessels can be shown by applying pressure to a red spot. If it is caused by an abnormal blood vessel the redness disappears temporarily. By contrast when pressure is applied to purpura the spots do not pale.

Purpura usually appears in crops and may disappear over three to five days. It can occur on any part of body but is more common on specific areas, such as the front of the shins.

What are the causes of purpura?

Purpura may occur when the platelet count of the blood is low (thrombocytopenia) but there are other causes too. It can occur when the blood vessel wall is particularly fragile, has been damaged, or if the skin is thin. In elderly people so-called 'senile purpura' is often seen on the outer surface of the arm and back of the hand. Similar features are seen in some patients treated with long-term steroid therapy because steroids weaken the connective tissues of the skin.

In some inflammatory conditions damage to the vessel wall, or 'vasculitis', may occur and can cause purpura. An example is the inflammatory disorder in children known as Henoch Schönlein purpura. In this there is abdominal pain, joint pain, kidney inflammation and raised purpura typically over the buttocks and limbs.

Purpura with painful bruising of the legs and around hair roots may also be seen in vitamin C deficiency or scurvy.

Purpura should be reported to a doctor for further investigation. In a person who is otherwise well this investigation can be done routinely. However, if the person with purpura is unwell, urgent investigation and treatment is required.

For details of specific types on thrombocytopenia see the factsheets on:

idiopathic thrombocytopenic purpura

thrombotic thrombocytopenic purpura

haemolytic uraemic syndrome.

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