What is the most likely diagnosis in a child presenting with urticarial skin lesions, fever, abdominal pain, facial edema, and leukocytosis?

Diagnosis: IgA Vasculitis (Henoch-Schönlein Purpura)

The constellation of urticarial skin lesions, fever, abdominal pain, facial edema (puffy face), and leukocytosis in a child is most consistent with IgA vasculitis (formerly Henoch-Schönlein purpura), which is the most common vasculitis in children. 1, 2

Key Diagnostic Features Supporting IgA Vasculitis

Clinical Presentation

• Palpable purpura or urticarial lesions are the hallmark cutaneous manifestation, typically appearing on the lower extremities and buttocks but can be widespread 1, 2
• Colicky abdominal pain is a frequent gastrointestinal manifestation and can be severe enough to mimic an acute surgical abdomen 1, 3
• Fever commonly accompanies the acute presentation 1
• Facial edema can occur as part of the systemic inflammatory response 2
• Leukocytosis is a characteristic laboratory finding during the acute phase 2

Critical Diagnostic Steps

Immediate evaluation should include:

• Skin biopsy of a fresh lesion (ideally <24 hours old) to confirm leukocytoclastic vasculitis with IgA deposition on direct immunofluorescence 4, 2, 5
• Urinalysis to detect proteinuria and/or hematuria, which occurs in up to 50% of cases and indicates renal involvement 2
• Complete blood count documenting the leukocytosis and checking for thrombocytopenia 2
• Inflammatory markers (ESR or CRP), which are typically elevated 4, 2
• Stool examination if gastrointestinal symptoms are prominent, as concomitant infections can complicate the presentation 1

Important Differential Diagnoses to Exclude

Urticarial Vasculitis

While urticarial vasculitis can present with similar skin findings, wheals in urticarial vasculitis persist for days (not hours) and resolve with residual bruising or hyperpigmentation 4, 6, 5. The presence of fever, abdominal pain, and systemic symptoms makes IgA vasculitis more likely than isolated urticarial vasculitis 5.

Incomplete Kawasaki Disease

This is a critical consideration that must not be missed because delayed treatment increases the risk of coronary artery aneurysms from 15-25% 7. Kawasaki disease should be strongly considered when:

• Fever persists ≥5 days with 2-3 principal clinical features 7
• The urticarial rash qualifies as the polymorphous exanthema criterion 7
• Facial swelling (puffy face) represents oral-cavity changes 7
• Abdominal pain is a recognized gastrointestinal manifestation 7
• Leukocytosis ≥12,000/mm³ is characteristic 7

Urgent echocardiography is mandatory to evaluate for coronary artery abnormalities, decreased left-ventricular contractility, mitral regurgitation, or pericardial effusion 7. If Kawasaki disease cannot be excluded, intravenous immunoglobulin (IVIG) must be administered within 10 days of fever onset to prevent irreversible cardiac damage 7.

Acute Hemorrhagic Edema of Infancy

In children under 2 years, acute hemorrhagic edema presents with low-grade fever, facial edema, and purpuric lesions but is benign with spontaneous recovery in 1-3 weeks without visceral involvement 8. The presence of significant abdominal pain and leukocytosis makes IgA vasculitis more likely 8.

Rocky Mountain Spotted Fever

Although RMSF can present with fever, rash, abdominal pain, and periorbital edema in children, the rash is typically maculopapular (not urticarial) appearing 2-4 days after fever onset and may become petechial 4. Thrombocytopenia is more characteristic than leukocytosis 4.

Management Algorithm

Once IgA vasculitis is confirmed:

1. Assess disease severity:

   • Monitor for gastrointestinal complications (hematemesis, hematochezia, intussusception) 1
   • Serial urinalysis to detect progressive renal involvement 2
   • Document extent of skin involvement and systemic symptoms 1

2. Initiate treatment based on severity:

   • Supportive care with hydration and analgesia for mild cases 1, 3
   • High-dose corticosteroids (typically 1-2 mg/kg/day prednisone) for severe abdominal pain, gastrointestinal bleeding, or significant renal involvement 1
   • Proton pump inhibitors if gastrointestinal symptoms are prominent 1

3. Monitor for complications:

   • Serial urinalysis weekly for the first month, then monthly for 6 months to detect delayed nephritis 2
   • Repeat stool examination if diarrhea or bloody stools develop, as concomitant infections occur in up to 42.9% of cases 1

Common Pitfalls to Avoid

• Do not dismiss the urticarial rash as a simple allergic reaction and treat with antihistamines alone; this delays diagnosis of a potentially serious systemic vasculitis 7
• Do not assume ordinary urticaria when fever and systemic symptoms are present; ordinary urticaria does not cause fever 9
• Do not overlook incomplete Kawasaki disease, especially in infants and young children with fewer than 5 principal features, as they remain at substantial risk for coronary complications 7
• Do not delay skin biopsy when wheals persist >24 hours or when systemic features suggest vasculitis 4, 6
• Do not fail to screen for renal involvement even when urinalysis is initially normal, as nephritis can develop weeks after the initial presentation 2