How can I differentiate classic Kawasaki disease from multisystem inflammatory syndrome in children (MIS‑C) and what are the recommended treatment strategies for each?

Differentiating Kawasaki Disease from MIS-C

MIS-C and Kawasaki disease share overlapping features but are distinguishable by age, gastrointestinal involvement, cardiac dysfunction pattern, and laboratory markers—with MIS-C requiring SARS-CoV-2 epidemiologic linkage and typically presenting with shock and myocarditis in older children, while classic KD presents with mucocutaneous features in younger children under 5 years. 1

Key Distinguishing Features

Epidemiologic and Demographic Differences

Age distribution is the most striking differentiator:

• KD: Predominantly affects children under 5 years (median age ~2-3 years) 2, 3
• MIS-C: Broader age range, typically school-age children and adolescents (median age ~7-9 years) 1, 2

Ethnic predisposition differs:

• MIS-C: Increased incidence in African, Afro-Caribbean, and Hispanic children; lower in East Asian descent 1
• KD: Higher incidence in East Asian populations

Critical requirement for MIS-C: Must have epidemiologic link to SARS-CoV-2 (positive PCR, positive serology, COVID-19-like illness, or close contact within 4 weeks) 1

Clinical Presentation Differences

Gastrointestinal involvement strongly suggests MIS-C:

• MIS-C: 84% have GI symptoms (diarrhea, abdominal pain, vomiting) 2, 3
• KD: Only 31% have GI symptoms 2

Cardiac involvement patterns differ markedly:

• MIS-C: Myocarditis with ventricular dysfunction (38.6%), shock (common), pericardial effusion (38.2%), mitral regurgitation (31.8%) 4, 5
• KD: Coronary artery aneurysms/ectasia (15-25% if untreated, 5% with IVIG treatment) 6, less ventricular dysfunction 1

Shock presentation:

• MIS-C: Frequently presents with hypotension/shock requiring ICU admission (33%) 2
• KD: Shock is uncommon (7.5% ICU admission) 2

Laboratory Markers for Differentiation

Laboratory findings that favor MIS-C over KD:

• Lower platelet count: MIS-C median 236 × 10³/µL vs KD 390 × 10³/µL 2
• Lower absolute lymphocyte count: MIS-C 2.59 × 10³/µL vs KD 3.92 × 10³/µL 2, 3
• Lower WBC count: MIS-C 11.56 × 10³/µL vs KD 16.30 × 10³/µL 2
• Markedly elevated procalcitonin: MIS-C 2.4 ng/mL vs lower in KD 2
• Markedly elevated ferritin: MIS-C 370 ng/mL vs lower in KD 2, 3
• Elevated troponin and BNP/pro-BNP: Much higher in MIS-C 3, 4
• Lower albumin and sodium: More pronounced in MIS-C 3

Laboratory findings that favor KD:

• Higher ESR: KD mean 73 mm/hr vs MIS-C 51 mm/hr 2
• Higher platelet count (especially after first week)
• Higher WBC with neutrophilia

Overlapping Features (Present in Both)

Both conditions can present with:

• Fever (persistent, >38°C)
• Conjunctivitis (bilateral, nonexudative)
• Oral mucosal changes (red/cracked lips, strawberry tongue)
• Rash (polymorphic, maculopapular)
• Extremity changes
• Elevated inflammatory markers (CRP, ESR)
• Elevated D-dimer and fibrinogen 3

Treatment Strategies

Kawasaki Disease Treatment 6

First-line therapy for KD:

• IVIG 2 g/kg (single infusion based on ideal body weight) within 10 days of fever onset
• Aspirin: High-dose (80-100 mg/kg/day divided QID) during acute phase until afebrile for 48-72 hours, then low-dose (3-5 mg/kg/day) for antiplatelet effect

For IVIG-resistant KD (persistent/recurrent fever ≥36 hours after initial IVIG):

• IVIG retreatment (2 g/kg) is first option
• Corticosteroids (methylprednisolone)
• TNF-α antagonists (infliximab)
• Abciximab in select cases

Long-term management stratified by coronary involvement:

• Risk Level I (no coronary changes): Low-dose aspirin for 6-8 weeks, no restrictions
• Risk Levels II-V (coronary involvement): Antiplatelet therapy ± anticoagulation, activity restrictions, serial cardiac monitoring 6

MIS-C Treatment 1

First-line therapy for MIS-C (moderate-to-high consensus):

• IVIG 2 g/kg (may divide into 1 g/kg daily × 2 days if cardiac dysfunction present)
• PLUS methylprednisolone 1-2 mg/kg/day IV (or equivalent steroid)

Key difference from KD: Glucocorticoids are recommended as part of first-line therapy in MIS-C, not reserved for refractory cases 1

For refractory MIS-C (persistent fever/ongoing organ involvement):

• High-dose methylprednisolone 10-30 mg/kg/day IV
• OR high-dose anakinra (IL-1 receptor antagonist)

Multidisciplinary management required: Pediatric rheumatology, cardiology, infectious disease, hematology 1

Clinical Algorithm for Differentiation

Step 1: Assess SARS-CoV-2 epidemiologic link

• If NO link → Consider KD
• If YES link → Proceed to Step 2

Step 2: Evaluate age

• Age <5 years with classic mucocutaneous features → Favor KD
• Age >5 years → Favor MIS-C

Step 3: Assess dominant clinical features

• Prominent GI symptoms + shock + myocarditis → MIS-C
• Classic mucocutaneous features without shock → KD

Step 4: Laboratory differentiation

• Low platelets + low lymphocytes + high procalcitonin + high ferritin + high troponin → MIS-C
• High WBC + high ESR + normal/high platelets → KD

Step 5: Cardiac assessment

• Ventricular dysfunction + shock → MIS-C
• Coronary artery dilation/aneurysms without shock → KD (though both can have coronary involvement) 1

Critical Pitfalls to Avoid

Do not delay treatment waiting for perfect diagnostic clarity: Both conditions require urgent immunomodulatory therapy to prevent cardiac complications. When uncertain, treat empirically based on dominant phenotype 1.

Do not assume MIS-C cannot develop coronary aneurysms: While less common than in KD, MIS-C patients without KD features can still develop coronary artery abnormalities 1, 5.

Do not use aspirin as monotherapy in suspected MIS-C: Unlike KD, MIS-C requires glucocorticoids as part of first-line treatment 1.

Younger children with MIS-C may present with KD-like features: Age alone is not sufficient for diagnosis; consider the full clinical picture including SARS-CoV-2 exposure 1.

Do not miss the diagnosis of KD during the pandemic: True KD unrelated to SARS-CoV-2 continues to occur and requires standard KD treatment 1.