IgA vasculitis is a condition where a specific type of antibody called IgA1 builds up in the walls of small blood vessels, triggering inflammation and damage. Previously known as Henoch-Schönlein purpura (HSP), it is the most common systemic vasculitis worldwide, with a global incidence estimated between 3 and 27 per 100,000 people. It primarily affects children, but adults can develop it too, and adults tend to have more serious complications.
How IgA Vasculitis Develops
The disease starts with a malfunction in how the body produces IgA1, one of the antibodies that normally protects mucous membranes in the gut and respiratory tract. In people who develop IgA vasculitis, the body produces a defective version of this antibody that’s missing a sugar molecule called galactose. This “galactose-deficient” IgA1 doesn’t behave normally. The immune system recognizes it as foreign and produces additional antibodies against it, forming clumps called immune complexes.
These immune complexes then lodge in the walls of small blood vessels in the skin, gut, joints, and kidneys. Once deposited, they activate an inflammatory cascade that damages the vessel walls and surrounding tissue. Researchers describe this as a “multi-hit” process: the body first produces defective IgA1, then generates antibodies against it, then the two combine into immune complexes, and finally those complexes settle into tissues and cause injury.
The initial trigger is often an infection. Respiratory tract infections are the most frequent precursor, identified in roughly two-thirds of cases. The leading theory is that a pathogen stimulates the mucosal immune system in a way that promotes abnormal IgA1 production, possibly through increased gut permeability or a process called molecular mimicry, where the immune system confuses the body’s own tissues with the invading pathogen.
Who Gets It
Children between ages 4 and 6 are at highest risk, with peak incidence reaching 70 cases per 100,000 in that age group. In the United States, the annual incidence in children is approximately 3 to 27 per 100,000, while adults develop it at a rate below 2 per 100,000. In parts of Asia, childhood incidence runs as high as 70 per 100,000. The condition occurs more often in fall and winter, which aligns with its connection to respiratory infections.
The Four Classic Symptoms
IgA vasculitis produces a recognizable pattern of four symptoms, though not everyone develops all four.
Skin rash (purpura). The hallmark is a rash of raised, bruise-like spots that range from red to deep purple depending on skin tone. It typically starts on the legs and feet but can spread to the buttocks, arms, face, chest, back, and abdomen. The rash tends to worsen in areas where clothing presses against the skin, like the sock line or waistband. Unlike bruises caused by low platelet counts, this purpura occurs while platelet levels remain normal.
Joint pain and swelling. Most patients experience painful, swollen joints, especially in the knees and ankles. Joint symptoms sometimes appear one to two weeks before the rash shows up, which can make early diagnosis tricky. The good news is that joint involvement resolves completely without lasting damage once the illness passes.
Abdominal symptoms. Between 50% and 75% of children with IgA vasculitis develop gastrointestinal symptoms: belly pain, nausea, vomiting, and sometimes bloody or black stools. These symptoms can also precede the rash. In rare cases, the intestinal inflammation leads to serious surgical complications. Intussusception, where part of the intestine folds into itself, occurs in roughly 1% to 14% of cases. Intestinal perforation is much rarer, at about 0.4%. Children under age 7 and those whose gut symptoms appear before the rash are at higher risk for these complications.
Kidney involvement. This is the most consequential feature. Kidney damage occurs in 20% to 50% of children and 45% to 85% of adults. Most kidney involvement develops early: 91% of cases appear within the first six weeks and 97% within six months. In many people, the only sign is protein or blood in the urine, detectable only through testing. Most children recover fully, with just 1% to 2% progressing to end-stage kidney disease. Adults face a steeper risk: about 13% develop severe kidney failure, and 10% to 30% progress to end-stage kidney disease within 15 years of diagnosis.
How It’s Diagnosed
The most widely used diagnostic framework requires the presence of purpura (the characteristic rash, without low platelets or a clotting disorder) plus at least one of the following: abdominal pain, joint pain or arthritis, kidney involvement (blood or protein in the urine), or a tissue biopsy showing IgA deposits.
A skin biopsy, when performed, is highly confirmatory. Under a specialized test called direct immunofluorescence, IgA deposits light up around the blood vessels in affected skin. Studies find IgA deposits in 75% to 100% of biopsied lesions, and about 60% of those also show a complement protein called C3, indicating active immune-mediated damage. In practice, the diagnosis is often made clinically based on the rash and accompanying symptoms, especially in children with a classic presentation. Biopsy is more commonly used when the picture is atypical or when kidney involvement needs to be assessed.
Treatment and Recovery
For most people, IgA vasculitis is self-limiting. Mild cases involving skin rash and joint pain are managed with rest, hydration, and over-the-counter pain relievers. Anti-inflammatory medications like ibuprofen can help with joint symptoms, but they’re avoided in patients who have kidney or gastrointestinal involvement because they can worsen bleeding and kidney function.
Compression stockings can help manage leg swelling. For skin disease that progresses to blistering, ulcers, or tissue breakdown, corticosteroids are typically needed. Corticosteroids are also the first-line treatment for adults with severe symptoms, significant gut complications, or kidney disease with moderate to heavy protein in the urine. Other medications like colchicine, dapsone, and methotrexate sometimes help control milder symptoms that don’t resolve on their own.
When kidney disease is severe, with large amounts of protein loss or declining kidney function, stronger immune-suppressing medications may be added. For the most critical or life-threatening situations, options include intravenous immunoglobulins or plasma exchange. Surgical intervention is reserved for rare gastrointestinal emergencies like perforation or intussusception that doesn’t resolve. If mild to moderate protein appears in the urine or blood pressure rises, medications that protect the kidneys by reducing pressure in the filtering units are often started.
Monitoring After Diagnosis
Because kidney damage can appear weeks or months after the initial illness, ongoing monitoring is essential. Current guidelines from the International Pediatric Nephrology Association recommend monthly urine checks for at least six months after diagnosis, even if initial tests are normal. If kidney involvement is detected, the monitoring schedule extends: monthly for six months, then every three months for another six months, then every six months for a minimum of five years. Children who required treatment for kidney disease may need lifelong monitoring, tailored to their severity and response.
Recurrence
About one in three children with IgA vasculitis will have at least one recurrence. In a large retrospective study, the recurrence rate was 34.7%, consistent with other research finding rates around 33%. Recurrences are often milder than the initial episode, but they still carry the risk of cumulative kidney damage. Respiratory tract infections remain the most common trigger for both initial episodes and relapses, so parents are often advised to be alert for returning symptoms after their child has been sick. Adults who develop the disease tend to have a more prolonged course and a higher chance of lasting kidney complications, making follow-up even more important in that group.