Henoch-Schönlein purpura (IgA vasculitis) is an immune complex-mediated, small-vessel systemic vasculitis characterized histologically by leukocytoclastic vasculitis with prominent immunoglobulin A (IgA) deposition within vessel walls ^{1, 2}. It represents the most frequent systemic vasculitis in the pediatric population, typically presenting between the ages of 2 and 10 years, with a predilection for males ⁶. The clinical phenotype is defined by the classic tetrad of non-thrombocytopenic palpable purpura predominantly over dependent areas, arthritis or arthralgia, gastrointestinal manifestations ranging from mild colicky pain to severe hemorrhage or intussusception, and renal involvement manifesting as hematuria and proteinuria ^{1, 3}. While the natural history is generally benign and self-limiting, long-term morbidity is primarily driven by progressive renal glomerular injury (IgA vasculitis nephritis) ^{5, 7}.

1. Etiology & Risk Factors

• Infectious Triggers: Frequently preceded by upper respiratory tract infections (most commonly Streptococcus pyogenes) or viral agents (adenovirus, parvovirus B19, Epstein-Barr virus, and varicella) ².
• Immunological Pathogenesis: Elevated serum levels of polymeric galactose-deficient IgA1 (Gd-IgA1) and corresponding IgG or IgA autoantibodies, resulting in circulating immune complex formation and vascular deposition ^{1, 2}.
• Environmental and Genetic Factors: Geographic and seasonal clustering (higher incidence in autumn and winter months) suggest environmental triggers superimposed on genetic susceptibility loci (such as MHC class II alleles) ^{1, 6}.
• Pharmacological Triggers: Rarely precipitated by specific medications, vaccinations (e.g., influenza or meningococcal vaccines), or insect stings acting as immune stimulants ².

2. Pathophysiology

The molecular cascade begins with mucosal exposure to infectious or environmental antigens in genetically susceptible hosts, triggering the aberrant synthesis of galactose-deficient IgA1 (Gd-IgA1) molecules by mucosal B cells. Autoantibodies (typically IgG or IgA directed against the hinge region of Gd-IgA1) bind to form circulating immune complexes. These complexes deposit within the microvasculature—specifically post-capillary venules in the skin, gastrointestinal tract, synovium, and renal mesangium. The localized deposition activates the alternative complement pathway, recruiting neutrophils and macrophages, releasing pro-inflammatory cytokines, and causing leukocytoclastic vasculitis characterized by fibrinoid necrosis, endothelial swelling, and microvascular hemorrhage ^{1, 2, 4}.

3. Clinical Presentation & Classic Clinical Signs

• History & Cardinal Symptoms: Patients typically present with a prodrome of low-grade fever, fatigue, and myalgia, followed sequentially or simultaneously by skin lesions, joint complaints, and visceral symptoms ^{3, 6}.
• Physical Examination & Named Clinical Signs:
  • Cutaneous Manifestations: Present in 100% of cases. Initial lesions appear as pinkish-red macules or wheals that rapidly evolve into classic palpable purpura, predominantly distributed symmetrically over the buttocks, lower extremities, and extensor surfaces of the arms, sparing the trunk. Severe cases may exhibit bullae or ulceration ^{1, 3}.
  • Musculoskeletal Manifestations: Occur in 60-84% of children, featuring periarticular tenderness and non-migratory oligoarthritis affecting large joints (knees and ankles), with preservation of joint architecture and absence of permanent deformity ^{1, 3}.
  • Gastrointestinal Manifestations: Present in 50-75% of patients, characterized by colicky, diffuse abdominal pain, nausea, vomiting, and occult or overt gastrointestinal bleeding secondary to submucosal hemorrhage and edema of the bowel wall ^{3, 6}.
  • Renal Manifestations: Seen in 20-54% of cases, manifesting as microscopic or macroscopic hematuria, non-nephrotic or nephrotic range proteinuria, and variable hypertension ^{1, 7}.

4. Diagnostic Workup & Interpretation (Laboratory, Imaging & ECG/Pathology)

5. Staging, Classification & Clinical Scoring Systems

6. Differential Diagnosis

7. Management & Treatment Protocol

• Initial Stabilization & Resuscitation: Assess airway, breathing, and circulation; ensure adequate hydration and electrolyte balance in patients with persistent vomiting or gastrointestinal fluid loss ³.
• First-Line Medical / Pharmacological Therapy (with exact adult dosing):
  • Supportive Care: Adequate hydration and pain control using simple analgesics (acetaminophen or non-steroidal anti-inflammatory drugs when renal function is robust) for arthralgia and mild abdominal pain ³.
  • Corticosteroids: Reserved for severe abdominal pain, gastrointestinal hemorrhage, or progressive nephritis. Oral prednisolone initiated at 1 to 2 mg/kg/day (maximum adult equivalent: 60 mg daily) tapered over 2 to 4 weeks ^{3, 5, 7}.
• Surgical / Interventional Indications: Urgent surgical consultation and reduction or resection required for confirmed bowel intussusception, bowel infarction, severe gastrointestinal perforation, or refractory bleeding ^{3, 4}.

8. Complications & Prognosis

• Acute Complications: Gastrointestinal hemorrhage, bowel necrosis, intestinal perforation, ileo-ileal intussusception, orchitis in males, and acute kidney injury ^{1, 3}.
• Chronic Complications: Long-term renal impairment progressing to chronic kidney disease or end-stage renal disease, occurring in approximately 1–5% of pediatric patients and a significantly higher proportion of adults (10–30%) ^{5, 7}.
• Prognosis: The vast majority of pediatric cases follow a benign, self-limiting course with complete spontaneous resolution within 4 to 6 weeks, though recurrence rates reach up to 30% within the first several months ³.