1. Memori
  2. ›
  3. Articles

"Purple Spots on the Legs" — IgA Vasculitis: From Diagnosis to Watching for Kidney Involvement

By Leon MoriguchiPublished May 15, 2026Updated May 18, 20264 min read日本語版あり
Audience
Parents whose child has been diagnosed with IgA vasculitis (Henoch-Schönlein purpura)

TL;DR

  • ·IgA vasculitis typically presents with its signature palpable purpura on the lower limbs and buttocks — alongside joint pain, abdominal pain, and potential nephritis — and most episodes resolve within four to six weeks with rest and symptom management
  • ·Kidney involvement occurs in about a third of cases and is the primary long-term concern; regular urinalysis for six months after diagnosis — even if the first test is normal — is the single most concrete action for protecting long-term renal outcomes
  • ·Recurrence happens in about one in three children, usually milder than the first episode; foamy urine, red urine, facial swelling, and severe abdominal pain are the home monitoring signals that warrant prompt return to a clinician

Contents

  1. Lead
  2. What IgA Vasculitis Is
  3. Natural Course and Recurrence
  4. Purpura Nephritis — The Most Important Long-Term Complication
  5. Home Monitoring
  6. Summary
  7. References

Lead

A few days after a cold, purple dots spread across the child's ankles and knees. The child complained of pain and refused to walk. Most parents who encounter this have no idea at first what they are looking at.

This is a typical presentation of IgA vasculitis (formerly called Henoch-Schönlein purpura, or HSP) — a form of vasculitis specific to childhood. The majority of cases resolve on their own, but a kidney complication — IgA vasculitis nephritis (purpura nephritis) — is the most important long-term concern.

What IgA Vasculitis Is

IgA vasculitis is a systemic vasculitis: inflammation of blood vessel walls, leading to vessel damage and reduced blood flow to affected tissues of small blood vessels, triggered by immune complex: a cluster of antigens bound to antibodies that can deposit in vessel walls and trigger local inflammation deposition (primarily IgA: immunoglobulin A, an antibody class that protects mucosal surfaces; abnormal IgA deposits trigger vessel inflammation in this disease) in vessel walls. It is the most common vasculitis in children [6]. A UK survey found an annual incidence of about 20 per 100,000 children, highest between ages 4 and 6 [7].

The four cardinal features:

  1. Purpura: small hemorrhages into the skin producing red or purple spots that do not blanch when pressed; caused here by vessel wall inflammation, not low platelets: palpable, non-thrombocytopenic: not caused by low platelet count; the purpura results from vessel wall damage rather than a clotting deficiency purpura favoring the lower limbs and buttocks. Platelet count is normal.
  2. Joint pain or arthritis: primarily affecting the knees and ankles; walking may become too painful.
  3. Abdominal pain: due to vasculitis of the gut wall; intussusception has been reported as a complication.
  4. Nephritis (purpura nephritis): manifests as hematuria: presence of blood in the urine, visible as pink or red color or detectable only on urinalysis and proteinuria: abnormal leakage of protein into the urine, indicating kidney filter damage.

The EULAR/PRINTO/PRES classification criteria published in 2010 require purpura with lower-limb predominance (mandatory) plus at least one of: abdominal pain, arthritis or arthralgia, kidney involvement, or IgA deposits on biopsy [2].

Natural Course and Recurrence

The majority of IgA vasculitis episodes resolve within four to six weeks. Some children require hospitalization — for severe abdominal pain or progressive nephritis — but the mainstay of management is rest and symptomatic treatment [1].

Recurrence occurs in roughly one third of cases [1]. Recurrent episodes are usually milder than the first and resolve spontaneously. Even so, recording symptoms and seeking medical review during recurrence remains important.

Corticosteroids are used when severe abdominal pain or progressive nephritis is present, but are not recommended for mild disease. NSAIDs (ibuprofen and similar agents) are used to relieve joint pain, though their use requires caution in the context of renal involvement — follow physician guidance.

Purpura Nephritis — The Most Important Long-Term Complication

In IgA vasculitis, the long-term issue that matters most is kidney involvement. Nephritis is reported in about a third of children (higher in studies of hospitalized patients) [3,4,5], appearing as hematuria and proteinuria.

Most cases of purpura nephritis resolve without intervention, but a small proportion progress to chronic kidney disease. Among unselected children with IgA vasculitis, fewer than 5% reach chronic kidney disease within 20 years of diagnosis [4]. No long-term kidney impairment has been reported in children whose urinalysis stayed normal; it occurred in about 1.6% of those with isolated urine abnormalities and in about one in five of those who developed nephritic or nephrotic syndrome [5]. Early detection and specialist involvement allow treatment to be considered in some cases.

About 85% of kidney involvement appears within four weeks of diagnosis and 97% within six months. For this reason, regular urinalysis is recommended for six months after diagnosis of IgA vasculitis, even if the first test is normal [5]. Monitoring whether blood or protein appears in the urine is the single most concrete action that protects long-term kidney outcomes.

Home Monitoring

The following signs are reasons to return to a clinician:

  • Red or pink urine: possible macroscopic hematuria — seek evaluation promptly
  • Foamy urine: can indicate heavy proteinuria
  • Swelling of the face or hands: possible protein loss from the kidneys (nephrotic syndrome)
  • Severe abdominal pain or repeated vomiting: raises the possibility of intussusception
  • Purpura spreading to the trunk or face: rare, but may signal more severe disease

Keeping a dated record of symptom progression — the extent of purpura, severity of abdominal pain, joint mobility — is useful when the child is seen again. "More than last week, or less" is a trend that only a parent's continuous observation can capture.

Summary

The acute phase of IgA vasculitis typically resolves on its own. What matters for long-term management is surveillance for kidney involvement. Regular urinalysis in the months following diagnosis, combined with home monitoring, is the practical foundation for protecting prognosis. The visual signal — purpura on the lower limbs — tends to prompt early presentation, but it is the follow-up that defines how well this condition is managed.

References

  1. Tizard EJ, Hamilton-Ayres MJ. Henoch Schonlein purpura. Arch Dis Child Educ Pract Ed. 2008;93(1):1–8. doi:10.1136/adc.2004.066035. PMID: 18208978.
  2. Ozen S, Pistorio A, Iusan SM, et al. EULAR/PRINTO/PRES criteria for Henoch-Schönlein purpura, childhood polyarteritis nodosa, childhood Wegener granulomatosis and childhood Takayasu arteritis: Ankara 2008. Part II: Final classification criteria. Ann Rheum Dis. 2010;69(5):798–806. doi:10.1136/ard.2009.116657. PMID: 20413568.
  3. Mir S, Yavascan O, Mutlubas F, Yeniay B, Sonmez F. Clinical outcome in children with Henoch–Schönlein nephritis. Pediatr Nephrol. 2007;22(1):64–70. doi:10.1007/s00467-006-0278-0. PMID: 17024391.
  4. Davin JC, Coppo R. Henoch-Schönlein purpura nephritis in children. Nat Rev Nephrol. 2014;10(10):563–573. doi:10.1038/nrneph.2014.126. PMID: 25072122.
  5. Narchi H. Risk of long term renal impairment and duration of follow up recommended for Henoch-Schonlein purpura with normal or minimal urinary findings: a systematic review. Arch Dis Child. 2005;90(9):916–920. doi:10.1136/adc.2005.074641. PMID: 15871983.
  6. Saulsbury FT. Henoch-Schönlein purpura. Curr Opin Rheumatol. 2001;13(1):35–40. doi:10.1097/00002281-200101000-00006. PMID: 11148713.
  7. Gardner-Medwin JM, Dolezalova P, Cummins C, Southwood TR. Incidence of Henoch-Schönlein purpura, Kawasaki disease, and rare vasculitides in children of different ethnic origins. Lancet. 2002;360(9341):1197–1202. doi:10.1016/S0140-6736(02)11279-7. PMID: 12401245.

In the memori app

The memori app keeps the course of a sick day in a form you can hand straight to a clinician.

  • Temperature and symptoms line up on one timeline: when it started, and how it moved.
  • Medicines are laid out by dose time, so a missed one is visible.
  • You can jot down what you want to ask before the appointment.
Try memori
← PreviousTamiflu and Abnormal Behavior — What Japan's Regulator Concluded, and Why "Don't Leave Them Alone for Two Days" Applies to Every DrugNext →"Fever Every Three to Four Weeks, Without Fail" — The Road to a PFAPA Diagnosis

Related

  • Stopping Impetigo from Spreading — Evidence on Antibiotics and Household Infection Control
  • When a Child Seems to Become a Stranger — Anti-NMDA Receptor Encephalitis and Autoimmune Encephalitis
  • Molluscum Contagiosum: Should You Treat It? — What the Meta-Analysis Actually Shows