Henoch-Schonlein purpura Dr Rob Hicks The body attacks its own blood vessels causing inflammation, rash and arthritis in this autoimmune reaction primarily affecting children.

In this article

What is Henoch-Schonlein purpura? Symptoms

Causes and risk factors Treatment and recovery

There are many health problems that arise from the fact that the body's immune system can turn on itself itself and attack its own tissues. These are called autoimmune reactions, and they can happen without warning. Henoch-Schonlein purpura (HSP) is one such reaction.

In HSP, the immune system is triggered to produce a type of antibody known as IgA which targets and attacks the blood vessels. This causes the blood vessels to become inflamed, a condition called vasculitis.

HSP often affects various parts of the body. Most patients are mildly unwell, with a low grade fever. A triad of more specific symptoms usually occurs:

• a characteristic symmetrical skin rash on the lower extremities
• abdominal pain or kidney problems
• arthritis

The characteristic rash of HSP appears as purple spots on the skin, known as purpura which may rapidly merge together to look like bruises. These are usually found over the lower extremities - in particular, the buttocks and lower legs. However, the rash can also appear on the face, trunk and upper extremities - especially the outer side of the arms. It tends to be more prominent in areas where pressure on the skin occurs, from socks or waistbands for example.

When the joints are affected, they may become red, swollen and tender. This is most common in the ankles and knees, but the feet, hands and elbows may also be involved. Fortunately, this is only temporary and permanent deformity doesn't occur.

Cramping abdominal pain, sometimes with diarrhoea and vomiting, and the passing of blood raises the alarm that the gut has become involved. In up to three percent of cases the bowel may become blocked by a condition called intussusception. Traces of blood or protein found in the urine indicates the kidneys are inflamed (called glomerulonephritis) - this affects up to 50% of older children.

It's thought that HSP may be triggered by a viral infection, as up to two-thirds of children will have had a respiratory tract infection (a cough or cold) one to three weeks before HSP appears. Other possible triggers include bacterial infections, vaccinations, medications, insect bites and food allergens.

HSP most often affects children between the ages of two and ten but people of any age can have it. It's slightly more common in girls than in boys, and occurs more frequently in the winter months. Every year in the UK about one person in every 5,000 develops HSP.

The condition usually settles down within six weeks, although it can go on for several months. It can recur, sometimes more than once, in as many as one in three people. There is no treatment which has been shown to shorten the duration of the disease or reduce the risk of complications, so no specific treatment is required. However, treatment can be used to relieve the symptoms. Paracetamol or non-steroidal anti-inflammatory medication (such as ibuprofen) may be prescribed to relieve any joint pain. If symptoms persist, corticosteroid therapy may be recommended.

The most serious possible consequence of Henoch-Schonlein purpura is kidney damage. Up to five percent of cases develop progressive kidney disease and ultimately kidney failure (this is more likely in older children and adults). For this reason, regular urine tests to monitor kidney function are important, even once someone has recovered from the acute illness.

In general, however, the majority of people who develop HSP make a full recovery without any further problems.

This article was last medically reviewed by Dr Trisha Macnair in February 2009.