Buy backpacks, exercise machines, athletic shoes, and more at Fogdog Sports. AP is also called Henoch-Schonlein purpura, named after the two doctors who first described it. In AP, this occurs because the capillaries are blocked by protein complexes formed during an abnormal immune reaction. The skin is the most obvious site of reaction, but the joints, gastrointestinal tract, and kidneys are also often affected. AP affects approximately 35,000 people in the United States each year.
Most cases are children between the ages of two and seven.
Boys are affected more often than girls, and most cases occur from late fall to winter. Antibodies are designed to bind with foreign proteins, called antigens. In some situations, antigen-antibody complexes can become too large to remain suspended in the bloodstream. When this occurs, they precipitate out and become lodged in the capillaries. This can cause the capillary to burst, allowing a local hemorrhage.