1 IgA vasculitis in children Vasculite por IgA em crianças Authors Maria Goretti Moreira Guimarães Penido 1,2 Lilian Monteiro Pereira Palma 3 1 Santa Casa de Belo Horizonte Hospital, Centro de Nefrologia, Unidade de Nefrologia Pediátrica, Belo Horizonte, MG, Brasil. 2 Universidade Federal de Minas Gerais, Hospital de Clínicas, Fa- culdade de Medicina, Unidade de Nefrologia Pediátrica, Belo Hori- zonte, MG, Brasil. 3 Universidade Estadual de Cam- pinas, Hospital de Clínicas, Ne- frologia Pediátrica, Campinas, SP, Brasil. DOI: https://doi.org/10.1590/2175-8239- JBN-2022-E002 Submitted on: 11/29/2021. Approved on: 12/01/2021. Correspondence to: Maria Goretti Moreira Guimarães Penido. E-mail:mariagorettipenido@yahoo.com.br. Immunoglobulin A (IgA) vasculitis (IgAV), classically known as Henoch- Schönlein purpura, is a type of non- thrombocytopenic small-vessel vasculitis and is the most frequent form of childhood systemic vasculitis (annual incidence: 3–26.7 per 100,000, depending on the country) 1-3 . IgAV is more frequent in childhood with a peak incidence around 4–6 years of age 2,4 . The disease usually presents with a palpable purpuric rash, gastrointestinal pain and bleeding, kidney involvement, arthralgia and/or arthritis 1-4 . Testicular inflammation (orchitis: 14% of male patients) is also seen, manifested by pain and swelling 5 . IgAV has a seasonal variation, suggesting a role for environmental triggers and geographic distribution, and has a slight male predominance 5 . It occurs more frequently in certain parts of the world, such as Korea and Japan, but has equal distribution in all ethnicity grups 5 . The presentation in adults differs from that in children; adults rarely have abdominal pain and frequently have joint involvement 5 . In 2013, the Revised Chapel Hill Consensus Conference defined IgAV at any age as a vasculitis with IgA-dominant immune deposits that affects small vessels, involving the skin, gut, and glomeruli, being associated with arthralgia or arthritis 6 . Kidney involvement is characterized by an IgA-dominant immune deposit indistinguishable from the pattern found in primary IgA nephropathy (IgAN). Criteria include a diagnosis of non-thrombocytopenic skin purpura with lower limb predominance as the main symptom and 1 of 4 additional criteria: 1) abdominal pain, 2) arthritis or joint pain, 3) kidney involvement (proteinuria >0.3 g/24h or a urine protein/creatinine ratio >30 mg/mmol on a spot morning sample or hematuria of >5 erythrocytes/high- power field), and 4) a leukocytoclastic vasculitis with predominant IgA deposits or kidney biopsy with predominant IgA deposits. Purpura with atypical distribution requires the presence of IgA deposits in the biopsy specimen 7 . IgAV is considered a benign disease in children (around 94% of affected children achieve full and spontaneous recovery within two years), but its prognosis depends on the extent and the progression of kidney involvement 1 . Overall, 40–50% of affected children have kidney involvement ranging from microscopic hematuria to rapidly progressive glomerulonephritis, contributing to 1–2% of all chronic kidney disease (CKD) stage 5. 2 In adults, the disease frequently occurs with atypical clinical features, severe kidney involvement, and with unfavorable outcome 3 . Recurrence (around 1/3 of patients) is more frequent in patients with kidney involvement and its duration is usually milder or shorter than the original episode 4 . Genetics plays a role in determining the appearance of the disease and its severity, although there is no clear genetic correlation with primary IgAN 3,5 . It is very likely that the complement system is involved in addition to the coagulation and fibrinolytic systems 8 . Activation of the complement system in an environment of endothelial cell damage could lead to thrombotic microangiopathy 3 .