allergic purpura

Allergic Purpura 

Definition

Allergic purpura (AP) is an allergic reaction of unknown origin causing red patches on the skin and other symptoms. AP is also called Henoch-Schonlein purpura, named after the two doctors who first described it.

Description

"Purpura" is a bleeding disorder that occurs when capillaries rupture, allowing small amounts of blood to accumulate in the surrounding tissues. 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.

Causes and symptoms

Causes

AP is caused by a reaction involving antibodies, special proteins of the immune system. 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.

The source of the antigen causing AP is unknown. Antigens may be introduced by bacterial or viral infection. More than 75% of patients report having had an infection of the throat, upper respiratory tract, or gastrointestinal system several weeks before the onset of AP. Other complex molecules can act as antigens as well, including drugs such as antibiotics or vaccines. Otherwise harmless substances that stimulate an immune reaction are known as allergens. 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.

Symptoms

The onset of AP may be preceded by a headache, fever, and loss of appetite. Most patients 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 patients, along with blood in the body waste (feces). About half of all patients 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 5% of all patients, and in 15% of those with elevated blood or protein in the urine.

Less common symptoms include prolonged headache, fever, and pain and swelling of the scrotum. Involvement of other organ systems may lead to heart attack (myocardial infarction), inflammation of the pancreas (pancreatitis), intestinal obstruction, or bowel perforation.

Diagnosis

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 scans (CT) may be performed to assess complications in the bowel or other internal organs.

Treatment

Most cases of AP resolve completely without treatment. Nonetheless, a hospital stay is required because of the possibility of serious complications. Non-aspirin pain relievers may be given for joint pain. Corticosteroids (like prednisone) are sometimes used, although not all specialists agree on their utility. Kidney involvement requires monitoring and correction of blood fluids and electrolytes.

Key terms

Glomeruli — Knots of capillaries in the kidneys responsible for filtering the blood (singular, glomerulus).

Patients 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 monitoring. Hypertension or kidney failure may develop months or even years after the acute phase of the disease. Kidney failure requires dialysis or transplantation.

Prognosis

Most people who develop AP become better on their own after several weeks. About half of all patients have at least one recurrence. Cases that do not have kidney complications usually have the best prognosis.

Resources

Periodicals

Andreoli, S. P. "Chronic Glomerulonephritis in Childhood. Membranoproliferative Glomerulonephritis, Henoch-Schonlein PurpuraNnephritis, and IgA Nephropathy." Pediatric Clinics of North America 42, no. 6 (December 1995): 1487-1503.

Other

"Henoch-Schonlein Purpura." Vanderbilt University Medical Center. 〈http://www.mc.vanderbilt.edu/peds/pidl/nephro/henoch.html〉.

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purpura /pur·pu·ra/ (pur´pu-rah)

1. a small hemorrhage in the skin, mucous membrane, or serosal surface.

2. a group of disorders characterized by the presence of purpuric lesions, ecchymoses, and a tendency to bruise easily.purpu´ric

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allergic purpura , anaphylactoid purpura Henoch-Schönlein p.

purpura annula´ris telangiecto´des  a rare form in which punctate erythematous lesions coalesce to form an annular or serpiginous pattern.

fibrinolytic purpura  purpura associated with increased fibrinolytic activity of the blood.

purpura ful´minans  nonthrombocytopenic purpura seen mainly in children, usually after an infectious disease, marked by fever, shock, anemia, and sudden, rapidly spreading symmetrical skin hemorrhages of the lower limbs, often associated with extensive intravascular thromboses and gangrene.

purpura hemorrha´gica  idiopathic thrombocytopenic p.

Henoch's purpura  Henoch-Schönlein purpura in which abdominal symptoms predominate.

Henoch-Schönlein purpura  nonthrombocytopenic purpura of unknown cause, usually in children; associated with symptoms such as urticaria, erythema, arthropathy and arthritis, gastrointestinal disorder, and renal involvement.

idiopathic thrombocytopenic purpura  thrombocytopenic purpura not directly associated with a systemic disease, although often following a systemic infection; believed to be due to an IgG immunoglobulin that acts as an antibody against platelets.

malignant purpura  meningococcal meningitis.

nonthrombocytopenic purpura  purpura without any decrease in the platelet count of the blood.

Schönlein purpura  Henoch-Schönlein purpura with articular symptoms and without gastrointestinal symptoms.

Schönlein-Henoch purpura  Henoch-Schönlein p.

purpura seni´lis  dark purplish red ecchymoses occurring on the forearms and backs of the hands in the elderly.

thrombocytopenic purpura  any form in which the platelet count is decreased, occurring as a primary disease (idiopathic thrombocytopenic p.) or as a consequence of a primary hematologic disorder (secondary thrombocytopenic p.) .

thrombotic thrombocytopenic purpura  a form of thrombotic microangiopathy marked by thrombocytopenia, hemolytic anemia, neurological manifestations, azotemia, fever, and thromboses in terminal arterioles and capillaries.

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allergic purpura

n.

1. Nonthrombocytopenic purpura due to sensitization to foods, drugs, or insect bites. Also called anaphylactoid purpura.

2. See Henoch-Schonlein purpura.

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allergic purpura

Etymology: Gk, allos, other, ergein, to work; L, purpura, purple

a chronic disorder of the skin associated with urticaria, erythema, asthma, and rheumatic joint swellings. Unlike in other forms of purpura, the platelet count, the bleeding time, and blood clotting are normal. Nonthrombocytopenic purpura is due to sensitization to foods, drugs, and insect bites.

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purpura (pur´pyoor),

n an extravasation of blood into the tissues, resulting in blue to black lesions of the skin or mucosa (petechiae and ecchymoses).

Purpura.

purpura, allergic,

n (anaphylactoid purpura) a thrombocytopenic or nonthrombocytopenic purpura related to an allergic reaction. Manifestations include the common symptoms of allergy.

purpura, anaphylactoid

n See purpura, allergic.

purpura, essential,

n See purpura, thrombocytopenic, idiopathic.

purpura hemorrhagica

n See purpura, thrombocytopenic and purpura, thrombocytopenic, idiopathic.

purpura, idiopathic thrombocytopenic,

n (essential purpura, land scurvy, primary purpura, purpura hemorrhagica) a type of unknown cause.

purpura, nonthrombocytopenic,

n a type related to increased capillary permeability. Included are allergic purpuras and those resulting from vitamin C deficiency, bacterial toxins (scarlet fever, typhoid), drug intoxications, and metabolic toxins (nephritis, liver disease).

purpura, primary,

n See purpura, thrombocytopenic, idiopathic.

purpura, secondary,

n See purpura, thrombocytopenic, symptomatic.

purpura, symptomatic thrombocytopenic,

n (secondary purpura) a type resulting from the effects of chemical, physical, vegetable, or animal agents or infections or related blood disorders.

purpura, thrombocytopathic

n a type associated with qualitative abnormalities of the platelets.

purpura, thrombocytopenic

n (essential thrombopenia, pseudohemophilia, hemorrhagica, Werlhof's disease) a type characterized by severe ecchymoses and petechiae associated with marked reduction in the numbers of blood platelets. There is prolonged bleeding time and poor clot retraction, but the coagulation and prothrombin times are normal. Hemorrhage may occur spontaneously from any area of the oral mucosa. This disease may be acute and fatal, whereas in other instances it may run a chronic course with intermittent attacks.

purpura, thrombotic thrombocytopenic,

n a febrile disease of unknown cause characterized by hemolytic anemia, neurologic symptoms, hemorrhage into the skin and mucous membranes, icterus, hepatosplenomegaly, low platelet count, and platelet thrombi occluding capillaries and arterioles.