Allergic purpura
Allergic purpura is an allergic disorder. The joints (usually knees, ankles, hips,
wrists, and elbows), the skin of the legs, thighs, and abdomen, the gastrointestinal
tract, and the kidneys are involved. Allergic purpura can affect both sexes, all ages, but
is more common in boys (2 to 8 years).
Appropriate health care includes:
Home care after diagnosis. Physician's monitoring of general condition and medications.
Hospitalization (for complications).
Description of Allergic purpura
"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 of Allergic purpura
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 of Allergic purpura
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 of Allergic purpura
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 of Allergic purpura
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.
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.
Plasmapheresis, which removes antibodies from the blood, has been tried for AP with
mixed results.
Prognosis of Allergic purpura
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.
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