What is the diagnosis for a 5-year-old child with fever, rash on the palms and soles, leukocytosis (high White Blood Cell (WBC) count), elevated erythrocyte sedimentation rate (SED rate), and thrombocytosis (high platelet count)?

Kawasaki Disease

This 5-year-old child has Kawasaki disease until proven otherwise, and requires immediate echocardiography and treatment with intravenous immunoglobulin (IVIG) 2 g/kg plus high-dose aspirin (80-100 mg/kg/day divided into four doses) to prevent coronary artery aneurysms. 1

Clinical Presentation Matches Classic Kawasaki Disease

The constellation of findings in this child is highly characteristic:

• Fever for ≥5 days is the cornerstone diagnostic feature 1
• Rash on palms and soles represents the extremity changes (erythema and edema of hands/feet with sharp demarcation at wrists/ankles) that is one of the five principal clinical features 1, 2
• Elevated WBC count (leukocytosis with neutrophil predominance) is typical, with approximately 50% of patients having counts >15,000/mm³ 1
• Elevated ESR is nearly universal in Kawasaki disease, often >40 mm/hour and commonly ≥100 mm/hour 1
• Thrombocytosis (high platelets) typically appears in the second week after fever onset, which fits this presentation 1

Diagnostic Criteria

The diagnosis requires fever ≥5 days plus ≥4 of the following 5 principal features: 1

1. Bilateral bulbar conjunctival injection without exudate
2. Oral mucosal changes (erythema/cracking of lips, strawberry tongue, pharyngeal erythema)
3. Polymorphous rash (maculopapular, diffuse erythroderma, or erythema multiforme-like)
4. Extremity changes (erythema and edema of hands/feet in acute phase; periungual desquamation in subacute phase)
5. Cervical lymphadenopathy (≥1.5 cm diameter)

The child already has confirmed fever, extremity changes (palms/soles rash), and laboratory evidence of systemic inflammation. 1

Critical Laboratory Findings Supporting the Diagnosis

The laboratory profile is classic for Kawasaki disease: 1

• Leukocytosis with immature and mature granulocyte predominance
• Elevated acute phase reactants (ESR and CRP are nearly universal)
• Thrombocytosis appearing after day 7 of illness (>450,000/mm³ is a supplemental criterion)
• Additional supportive findings may include: anemia for age, hypoalbuminemia (<3.0 g/dL), elevated ALT, and sterile pyuria (>10 WBC/hpf) 1

Why This Matters: Coronary Artery Complications

Without treatment, 15-25% of children develop coronary artery aneurysms or ectasia, which can lead to myocardial infarction, sudden death, or ischemic heart disease. 1, 3, 4 Treatment with IVIG within 10 days of fever onset reduces this risk from 25% to approximately 5%. 2

Immediate Management Algorithm

Step 1: Obtain echocardiography immediately 1

• Even though aneurysms rarely form before day 10, early findings may include perivascular brightness, ectasia, lack of tapering, decreased LV function, mitral regurgitation, or pericardial effusion 1
• If coronary abnormalities are present with only 3 clinical features, the diagnosis is confirmed 1

Step 2: Initiate treatment without delay 1

• IVIG 2 g/kg as a single infusion (first-line, Level A evidence)
• High-dose aspirin 80-100 mg/kg/day divided into four doses given concurrently with IVIG
• Treatment should begin as soon as the diagnosis is suspected, ideally within 10 days of fever onset 1, 2

Common Diagnostic Pitfalls to Avoid

Do not dismiss this as a viral illness or drug reaction simply because the full criteria aren't initially apparent. 1 Critical mistakes include:

• Misdiagnosing as bacterial lymphadenitis when cervical adenopathy is prominent, then attributing subsequent rash to antibiotic reaction 1
• Mistaking sterile pyuria for partially treated UTI 1
• Missing the diagnosis in infants <6 months who often present with incomplete Kawasaki disease and have the highest risk for coronary complications 1, 5, 4
• Waiting for all five clinical features to appear simultaneously—they may evolve over days, requiring careful history-taking 1

Differential Diagnosis Considerations

Features that would argue against Kawasaki disease include: 1

• Exudative conjunctivitis or pharyngitis
• Discrete intraoral ulcerations
• Vesicular or bullous rash
• Generalized (rather than cervical) lymphadenopathy

The absence of vesicular lesions distinguishes this from hand-foot-mouth disease, which presents with discrete vesicles rather than diffuse erythema. 6 The duration of fever (≥5 days) and laboratory findings (markedly elevated ESR/platelets) distinguish this from viral exanthems like roseola. 7

Risk Stratification

This child is at particularly high risk if: 1

• Fever persists beyond 10 days (powerful predictor of coronary aneurysms)
• Age <1 year (paradoxically higher aneurysm rate despite incomplete presentations)
• Male sex
• Specific laboratory thresholds: WBC >12,000/mm³, platelets after day 7 >450,000/mm³, hemoglobin <10 g/dL, albumin <3.5 g/dL

All patients diagnosed with Kawasaki disease should receive IVIG regardless of risk stratification, as scoring systems have imperfect predictive value. 1