What is Allergic Purpura?
Allergic purpura (AP), also called Henoch-Schonlein purpura, is a disease in which blood vessels in the skin, joints, digestive tract, or kidneys become inflamed and may leak. The term allergic purpura applies to purpura associated with many other conditions, such as erythema nodosum. An acute attack of allergic purpura can last for several weeks and is potentially fatal (usually from kidney failure).
Allergic purpura, an uncommon disease, affects mainly young children, but it can affect older children and adults. The disease is believed to result from an autoimmune reaction, in which the body attacks its own tissues. Usually, Allergic purpura develops after a respiratory tract infection, but it can develop after an immunization or an insect bite or be caused by an allergic reaction to drugs or food. The rate at which the disease develops and its duration vary.
Allergic purpura occur suddenly. The characteristic rash is always present in the disease. The rash begins as areas of redness and as small hives, which may develop on the body, 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) 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.
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.
Causes of Allergic Purpura?
The most common cause of allergic purpura is an autoimmune reaction directed against vascular walls, triggered by a bacterial infection. Typically, upper respiratory infection occurs 1 to 3 weeks before the onset of symptoms. Other possible causes include allergic reactions to some drugs (such as penicillin, ampicillin, erythromycin, and quinine). Vaccines possibly linked to AP include those for typhoid, measles, cholera, and yellow fever.