What is the most likely cause of abdominal pain, bilateral ankle swelling, hematuria, and proteinuria in a child with a history of Henoch-Schönlein Purpura (HSP) and a family history of Systemic Lupus Erythematosus (SLE)?

Most Likely Diagnosis: HSP Nephritis (Expected Systemic Vasculitis Manifestation)

The most likely cause of this child's presentation is HSP nephritis, which is an expected manifestation of the systemic vasculitis already diagnosed. The constellation of abdominal pain, bilateral ankle swelling (arthritis/arthralgia), hematuria, and proteinuria represents classic multi-system involvement of HSP, not a new disease process 1.

Clinical Reasoning

Why This is HSP Nephritis (Option C)

Renal involvement occurs in approximately 20-50% of children with HSP and represents expected disease progression rather than a separate diagnosis 2. The clinical presentation fits the diagnostic criteria perfectly:

• Palpable purpura (previously diagnosed HSP) plus at least one of the following 3:
  • Renal involvement (hematuria and/or proteinuria) ✓
  • Arthralgia/arthritis (bilateral ankle swelling) ✓
  • Abdominal pain ✓

The triad of hematuria, purpuric lesions, and ankle pain is specifically diagnostic of HSP 3. This child has all three manifestations, making HSP with nephritis the most parsimonious diagnosis.

Why NOT Early SLE Nephritis (Option A)

While the family history of SLE raises concern, family history alone does not justify diagnosing a new autoimmune disease when the current symptoms are entirely consistent with the known HSP diagnosis 1.

Key distinguishing factors:

• HSP nephritis typically presents with hematuria and proteinuria in the context of active systemic disease (abdominal pain, arthritis) 4, 2
• SLE would require additional diagnostic criteria beyond renal manifestations (positive ANA, anti-dsDNA, low complement levels, other organ involvement) 5
• The vast majority of children with HSP and renal involvement have self-limited disease 1

Important caveat: While rare case reports document SLE initially mimicking HSP 5, this represents diagnostic overlap rather than the most likely scenario. If the child fails to respond to HSP-directed therapy or develops additional features (serositis, positive autoantibodies), SLE should be reconsidered 5.

Why NOT JIA (Option B)

Bilateral ankle swelling in the context of HSP is arthralgia/arthritis from vasculitis, not JIA 3, 4. JIA would not explain:

• The hematuria and proteinuria
• The abdominal pain
• The temporal relationship to known HSP diagnosis

Immediate Management Approach

Diagnostic Workup Required

Urinalysis with microscopy is essential to assess severity of glomerulonephritis 3:

• Look for red blood cell casts and dysmorphic RBCs (indicate glomerular involvement) 3
• Quantify proteinuria 1

Basic metabolic panel including BUN, creatinine, and complete blood count to assess renal function 3.

Blood pressure measurement is essential as hypertension indicates more severe renal involvement 3.

Renal biopsy should be performed if 1:

• Decreased renal function at presentation
• Severe nephrotic syndrome (proteinuria >3.5 g/day) or nephritic syndrome
• Deteriorating kidney function

Treatment Algorithm Based on Severity

For persistent proteinuria 0.5-1 g/day per 1.73 m²:

• Start ACE inhibitor or ARB therapy 1, 3
• Target proteinuria to <1 g/day/1.73 m² (not complete normalization, which increases side effects without proven benefit) 3

For persistent proteinuria >1 g/day per 1.73 m² after ACE-I/ARB trial and GFR >50 ml/min per 1.73 m²:

• Consider 6-month course of corticosteroid therapy 1, 3
• Do not start corticosteroids for mild proteinuria without adequate trial of ACE-I/ARB first 3

For crescentic HSP with nephrotic syndrome and/or deteriorating kidney function:

• Treat with high-dose intravenous methylprednisolone plus cyclophosphamide 1, 3
• Follow same protocol as crescentic IgA nephropathy 1

Critical Pitfalls to Avoid

Do NOT use corticosteroids prophylactically at HSP onset to prevent nephritis—moderate quality evidence (Level 1B) shows no benefit 1, 3.

Do NOT delay imaging or assume isolated hematuria requires no evaluation if an abdominal mass is palpable, as this could represent a separate pathology like Wilms tumor 6.

Do NOT use NSAIDs (like ketorolac/Toradol) for pain control in HSP patients with renal involvement, as they can cause acute kidney injury 3. Use acetaminophen as first-line analgesic 3.

Follow-up Protocol

Monitor for at least 6 months with regular urine testing for proteinuria and hematuria, plus blood pressure measurements 7, 3.

Women with childhood HSP history are at increased risk of complications (proteinuria, hypertension) during pregnancy and require close monitoring 7.

1, 3, 7, 5, 4, 2