Allergic purpura


Allergic purpura (AP), a form of vasculitis (inflammation of the blood vessels), is a disease characterized by inflammation of the small arterial vessels (capillaries) in the skin, kidneys, and intestinal tract. Symptoms include a purple spotted skin rash, abdominal pain , gastrointestinal upsets, and joint inflammation, swelling, and pain. Although the exact cause of the disease is unknown, it often develops following a recent viral or bacterial infection of the respiratory tract and is an abnormal reaction of the immune system to the infection.


AP may occur suddenly, or it may develop slowly over a period of weeks. The characteristic rash is always present in the disease. The rash begins as areas of redness and as small hives , which may develop anywhere on the body, but especially on the legs and buttocks, and may itch. The rash is caused by inflamed capillaries rupturing, allowing small amounts of blood to accumulate in the surrounding tissues. Through time the rash changes color from red to a bruised, purple color. Each rash spot will last about five days, and the rash can reoccur several times. The skin rash is the most obvious symptom of AP but is not the most serious, for the joints, gastrointestinal tract, and kidneys may also be affected.

Joint inflammation (arthritis), especially of the knees and ankles, occurs in two-thirds of the children affected by AP. The joints become swollen, tender, and painful with movement; the pain may be debilitating. However, the arthritis usually clears up with no permanent damage.

Gastrointestinal symptoms are a result of inflammation and bleeding of the capillaries in the gastrointestinal tract, including the mouth, esophagus, stomach, and intestines. Most children with AP experience severe abdominal pain, vomiting (possibly with blood), and bloody stools.

The most serious complication of AP is kidney inflammation (nephritis), which occurs in almost half of older affected children. Symptoms include blood and protein in the urine. Most children whose kidneys are affected recover fully, but about 10 percent later develop more serious chronic kidney disease. In 80 percent of those with kidney involvement, the kidney disease develops within the first four weeks of illness.

Children younger than three years who contract AP have a shorter, milder course of the disease with fewer recurrences. Older children are more likely to have more serious symptoms.

AP is also called Henoch-Schonlein purpura, named after the two German physicians who first recognized and described it in the 1880s. AP is also referred to as anaphylactoid purpura or vascular purpura.


AP is the most common acute vasculitis affecting children. In the United States, the prevalence of AP is approximately 14 to 15 cases per 100,000 population. Approximately 75 percent of cases occur in children between the ages of two and 11, with peak prevalence in children aged five years. AP is rare in infants and younger children. Boys are affected more often than girls (the female-to-male ratio is 1.5-2:1). Most cases occur in late fall and winter. Adults can also develop the disease.

Causes and symptoms


AP is caused by reactions of antibodies binding with foreign proteins, called antigens. In some cases, the antigen-antibody complexes become too large to remain suspended in the bloodstream. When this occurs, they precipitate out and become lodged in the capillaries, which can cause the capillary to burst, resulting in a local hemorrhage.

The source of the antigens that cause AP is unknown. Antigens may be introduced by bacterial or viral infection, because more than 75 percent of children with AP report having had an infection of the throat, upper respiratory tract, or gastrointestinal system several weeks before the onset of AP. AP may also be caused by allergens, which are otherwise harmless substances that stimulate an immune reaction. Drug allergens that may cause AP include penicillin, ampicillin, erythromycin, and quinine. Vaccines possibly linked to AP include those for typhoid, measles , cholera, and yellow fever. Food allergens, cold exposure, and insect bites have also been associated with AP.


The onset of AP may be preceded by a headache , fever, and loss of appetite. Most children first develop an itchy skin rash. The rash is red, either flat or raised, and may be small and freckle-like. The rash may also be larger, resembling a bruise. Rashes become purple and then rust-colored over the course of a day, and fade after several weeks. Rashes are most common on the buttocks, abdomen, and lower extremities. Rashes higher on the body may also occur, especially in younger children.

Joint pain and swelling is common, especially in the knees and ankles. Abdominal pain occurs in almost all children with AP, along with blood in the stools. About half of all affected children show blood in the urine, low urine volume, or other signs of kidney involvement. Kidney failure may occur due to widespread obstruction of the capillaries in the filtering structures called glomeruli. Kidney failure develops in about 2–5 percent of all affected children and in 15 percent of those with elevated blood or protein in the urine.

Less common symptoms include prolonged headache, fever, and pain and swelling of the scrotum, scalp, eyelids, lips, ears, backs of the hands and feet, and perineum. Involvement of other organ systems may lead to heart attack (myocardial infarction), inflammation of the pancreas (pancreatitis), intestinal obstruction, bowel perforation, or acute intussusception (a twisting inversion of the lining of the bowel).


Diagnosis of AP is based on the symptoms and their development, a careful medical history, and blood and urine tests. X rays or computed tomography (CT) scans may be performed to assess complications in the bowel or other internal organs. In some cases a renal biopsy may be useful to determine the extent of kidney involvement.

When to call the doctor

A doctor should be consulted if a child exhibits symptoms of AP. After a child has had an episode of AP, the doctor should be called if the child experiences sudden increases in abdominal pain, which may indicate a bowel infarction or perforation, or if the child exhibits decreased urine output, indicating kidney disease.


Most cases of AP resolve completely without treatment. Nonetheless, a hospital stay with supportive treatment is usually required because of the possibility of serious complications. Non-aspirin pain relievers may be given for joint pain. Corticosteroids (such as prednisone) are sometimes used to alleviate gastrointestinal tract inflammation but have not been shown to be effective for associated kidney problems. Kidney involvement requires monitoring and correction of blood fluids and electrolytes. Salt intake should be restricted. A child with AP should be monitored until abnormal urinary findings subside.

Children with severe kidney complications may require a kidney biopsy so that tissue can be analyzed. Even after all other symptoms subside, elevated levels of blood or protein in the urine may persist for months and require regular long-term monitoring. Hypertension or kidney failure may develop months or even years after the acute phase of the disease. Kidney failure requires dialysis or transplantation.

Surgery may be necessary to correct acute intussusception of the bowel.


AP may be mild, lasting only two or three days. However, for those children with moderate to severe symptoms, AP may last for four to six weeks, with relapses in about half of all children within six weeks, especially if the child contracts another respiratory infection or is exposed to the allergic agent. Relapses can occur up to seven years after the initial disease. Full recovery occurs in most cases without kidney involvement. However, one fourth of children who have kidney symptoms still have detectable problems years later. There is a higher likelihood of permanent renal damage with a higher number of recurrences.


If the initiating trigger for a case of AP is identified in an affected child, everything possible should be done to ensure that the child is not exposed to that substance again. If the cause is thought to be a bacterial infection, such as strep throat , prophylactic antibiotic treatment is sometimes given once the infection has been treated to prevent recurrence.

Parental concerns

Parents should be vigilant regarding recurrence of symptoms after their child has had AP. Parents should also realize that although severe kidney involvement is rare, if it does occur, it may require aggressive treatment and long-term care. If the child does have long-term kidney problems, the stress of the illness can often be mitigated by parents joining a support group in which members share common experiences and problems.


Capillaries —The tiniest blood vessels with the smallest diameter. These vessels receive blood from the arterioles and deliver blood to the venules. In the lungs, capillaries are located next to the alveoli so that they can pick up oxygen from inhaled air.

Glomerulus —Plural, glomeruli; a network of capillaries located in the nephron of the kidney where wastes are filtered from the blood.



Henoch-Schonlein Purpura: A Medical Dictionary, Bibliography, and Annotated Research Guide to Internet References. San Diego, CA: Icon Health Publications, 2004.


National Kidney Foundation. 30 East 33rd St., Suite 1100, New York, NY 10016. Web site:


Scheinfeld, Noah S., et al. "Henoch-Schoenlein Purpura." emedicine , October 8, 2004. Available online at (accessed November 28, 2004).

Judith Sims Richard Robinson

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