In a 7‑year‑old boy with palpable purpuric rash on legs and buttocks, knee and ankle arthralgias, colicky abdominal pain after an upper‑respiratory infection, and normal CBC, CMP, PT/PTT, which diagnosis is most likely: hemolytic‑uremic syndrome, idiopathic thrombocytopenic purpura, or IgA vasculitis (Henoch‑Schönlein purpura)?

IgA Vasculitis (Henoch-Schönlein Purpura) is the Most Likely Diagnosis

This 7-year-old boy has IgA vasculitis (formerly Henoch-Schönlein purpura), characterized by the classic tetrad of palpable purpura on dependent areas, arthralgias, abdominal pain, and preceding upper respiratory infection—all with normal platelet count and coagulation studies that definitively exclude ITP and hemolytic-uremic syndrome. 1, 2

Diagnostic Reasoning

Key Clinical Features Supporting IgA Vasculitis

• Palpable purpuric rash on the legs, buttocks, and backs of arms (dependent/extensor surfaces) that evolved from urticarial lesions is pathognomonic for small-vessel vasculitis, specifically IgA vasculitis 1, 2

• Preceding upper respiratory infection 3 weeks ago is the classic trigger, as IgA vasculitis frequently follows streptococcal or other respiratory infections 1, 3

• Arthralgias affecting knees and ankles with periarticular swelling but no effusion, erythema, or warmth fits the typical migratory, non-erosive arthritis pattern of IgA vasculitis 1, 2

• Colicky abdominal pain with nausea (without bloody stools) represents gastrointestinal involvement seen in up to 85% of IgA vasculitis cases 3, 2

• Age 7 years falls within the peak incidence (4-6 years old) for this most common childhood vasculitis 3, 2

Laboratory Findings That Exclude Alternative Diagnoses

• Normal CBC with normal platelet count definitively rules out idiopathic thrombocytopenic purpura (ITP), which requires thrombocytopenia (typically <30,000/μL) for diagnosis 4

• Normal PT/PTT excludes disseminated intravascular coagulation and coagulopathies 5

• Negative urinalysis at presentation is reassuring but does not exclude IgA vasculitis, as renal involvement can develop weeks to months after initial symptoms in up to 50% of cases 6, 3

• Normal comprehensive metabolic panel with presumably normal creatinine excludes hemolytic-uremic syndrome, which presents with acute renal failure (creatinine ≥1.0 mg/dL in children), microangiopathic hemolytic anemia with schistocytes, and typically follows bloody diarrhea 4, 5

Why Not ITP?

• ITP presents with non-palpable petechiae and ecchymoses (not palpable purpura), isolated thrombocytopenia without other systemic symptoms, and no arthralgias or abdominal pain 4

• The normal platelet count in this patient completely excludes ITP as a diagnosis 4

• ITP does not cause the characteristic rash distribution on extensor surfaces or the evolution from urticarial to purpuric lesions 7, 8

Why Not Hemolytic-Uremic Syndrome?

• HUS requires the triad of microangiopathic hemolytic anemia (with schistocytes on smear), thrombocytopenia, and acute renal failure 4, 5

• This patient has normal CBC (no anemia, no thrombocytopenia), normal urinalysis (no hematuria, no proteinuria), and normal metabolic panel (normal creatinine) 5

• HUS typically follows bloody diarrhea from Shiga toxin-producing E. coli, which this patient does not have 4, 5

• Neurological symptoms in HUS are late manifestations of severe disease with encephalopathy, not the arthralgias seen here 4

Management Approach

Immediate Actions

• Supportive care is the primary treatment, as 94% of children with IgA vasculitis experience spontaneous resolution 2

• Do not initiate corticosteroids prophylactically—systematic reviews demonstrate steroids do not prevent renal or gastrointestinal complications when used at disease onset 2

• Monitor for severe abdominal complications (intussusception, bowel perforation, massive GI bleeding) that would require hospitalization and high-dose corticosteroids 3, 2

• Ensure adequate hydration and pain control with acetaminophen; avoid NSAIDs due to potential renal effects 2

Renal Monitoring Protocol

• Obtain weekly urinalysis for 4-6 weeks, then monthly for 6 months to detect delayed renal involvement (hematuria, proteinuria) 3, 2

• Measure blood pressure at each visit, as hypertension indicates more severe nephritis 3

• If persistent proteinuria (>1 g/day) or nephrotic/nephritic syndrome develops, refer to pediatric nephrology for renal biopsy to guide immunosuppressive therapy 6, 3

• Long-term follow-up for 12 months minimum is essential, as renal disease can manifest years after initial presentation and accounts for 1-2% of childhood end-stage kidney disease 3, 2

Indications for Corticosteroid Therapy

• Severe abdominal pain unresponsive to supportive care or evidence of GI bleeding 2

• Moderate to severe nephritis (nephrotic-range proteinuria, declining renal function): use oral or IV corticosteroids plus azathioprine, mycophenolate mofetil, or cyclophosphamide depending on biopsy severity 3, 2

• Severe disease with nephritic/nephrotic syndrome: IV methylprednisolone with cyclophosphamide 3

Critical Pitfalls to Avoid

• Do not delay diagnosis waiting for skin biopsy—the clinical presentation is diagnostic, and biopsy is reserved for atypical cases or when distinguishing from other vasculitides 6, 2

• Do not assume normal initial urinalysis excludes renal involvement—up to 50% develop nephritis weeks to months later, making prolonged monitoring mandatory 6, 3

• Do not confuse palpable purpura with simple petechiae—palpability indicates vasculitis, not thrombocytopenia 7, 1

• Do not miss intussusception—if abdominal pain worsens or becomes localized with vomiting, obtain abdominal ultrasound or CT immediately 3, 2