What causes Henoch-Schönlein purpura?
Henoch-Schönlein purpura (HSP) is an immune-mediated condition. This means that it develops because of an abnormal reaction of the body's defence (immune) system. It is not clear exactly what causes this reaction but it is thought that something acts as a trigger for HSP. For example, the trigger may be a particular infection or certain medicines, such as certain antibiotics.
The trigger (called an antigen) stimulates the immune system to produce a chemical to fight against it (antibody) and attack it. This causes immune complexes to form which are then deposited in the small blood vessels under the skin. The immune complexes cause inflammation of the blood vessels.
Inflammation of the blood vessels is known as vasculitis. It is this inflammation that causes the small, round, red spots (petechiae) and the areas of reddish-purple skin discolouration (purpura). The immune complexes can also be deposited in other tissues of the body (for example, the kidneys), causing inflammation there as well.
The most common infection that has been found to be the trigger for HSP is an infection with a group of germs (bacteria) called Group A streptococcus. This group of bacteria is a common cause of infection of the upper respiratory tract - the throat and the upper airways. So, often, particularly in children, someone who develops HSP will have had a recent upper respiratory tract infection (within the previous few weeks).
Other bacterial and viral infections may also be triggers in some people. For example, parvovirus B19, Haemophilus parainfluenzae, Coxsackievirus and adenovirus.
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- Watson L, Richardson AR, Holt RC, et al; Henoch schonlein purpura--a 5-year review and proposed pathway. PLoS One. 2012 7(1):e29512. doi: 10.1371/journal.pone.0029512. Epub 2012 Jan 3.
- Henoch-Schönlein purpura; DermNet NZ
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