Allergic Purpura Health Article

Definition

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.

Description

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.

Demographics

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

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.