Henoch-Schonlein Purpura (HSP)

Henoch-Schonlein purpura is a small blood vessel vasculitis caused by deposits of immunoglobulin A (IgA). IgA is the main antibody found in mucosal cells lining the respiratory, gastrointestinal, and genitourinary tract. In HSP, the levels of IgA are elevated and can aggregate with other proteins to form immune complexes. These immune complexes get deposited in small blood vessels throughout the body, particularly in the gastrointestinal system, skin, joints, and kidneys. The deposit of immune complexes causes activation of the immune system resulting in vascular inflammation and damage to the blood vessels. 

Typically, HSP presents in childhood and usually develops 1 to 3 weeks after a mucosal infection, such as a viral upper respiratory tract infection or a group A streptococcal pharyngeal infection. The infection triggers IgA antibody production, forming more immune complexes that can be deposited in the blood vessel walls. The exact reason why the IgA complexes form in the first place is unclear, but genetic factors are likely to play an important role. 

Henoch-Schonlein purpura is associated with a classic tetrad of symptoms, including palpable purpura (i.e., raised skin rash consisting of red to purple spots typically located on the buttocks and legs), abdominal pain, hematuria or bloody urine, and arthritis. In addition, individuals with Henoch-Schonlein purpura can present with general symptoms like fever, malaise, and fatigue. Specific signs and symptoms depend on where the IgA immune complexes are deposited.  

Joint pain most commonly presents in the knees and ankles, which can result in limping. If the IgA immune complexes get deposited in the blood vessels of the gastrointestinal tract, it can cause colicky abdominal pain, as well as nausea and vomiting. In rare cases, there can be gastrointestinal bleeding, which can present as hematochezia (i.e., blood in stool) or hematemesis (i.e., blood in emesis). Additionally, a hematoma in the intestinal wall could cause intussusception, a condition that occurs when part of the intestine folds into another section of the intestines, resulting in bowel obstruction.  

In the kidneys, deposition of IgA immune complexes can lead to nephritic syndrome, which presents as blood in the urine, or hematuria. In some cases, the condition may progress to chronic kidney damage and even end-stage kidney failure. Less commonly, there may be other clinical manifestations, including inflammation of one or both testes (i.e., orchitis), as well as central nervous system involvement with headaches, behavioral changes, or seizures.