What are the signs of a polymorphous rash on extremities in a 1-year-old patient with suspected Kawasaki disease?

Signs of Polymorphous Rash on Extremities in Kawasaki Disease

In a 1-year-old with suspected Kawasaki disease, the polymorphous rash typically appears as erythematous maculopapular lesions that are truncal with groin accentuation, but extremity involvement manifests primarily as acute erythema and edema of the hands and feet with sharp demarcation at the wrists and ankles—not as the classic rash pattern itself. 1

Understanding the Polymorphous Exanthem

The term "polymorphous" describes the variability in rash appearance between different patients, not necessarily multiple morphologies in the same individual. 2 The rash presents in several accepted forms:

• Erythematous maculopapular eruption (most common presentation) 1
• Diffuse erythroderma 1
• Erythema multiforme-like pattern 1
• Urticarial or scarlatiniform appearance 1

The rash typically appears within the first 5 days of fever onset and shows truncal distribution with particular accentuation in the groin/perineal region. 1, 2

Specific Extremity Changes in Kawasaki Disease

The extremities in Kawasaki disease show distinct changes that are separate from the polymorphous rash and constitute one of the five principal diagnostic criteria:

Acute Phase Extremity Findings:

• Erythema of palms and soles with sharp demarcation at wrists and ankles 1
• Edema of hands and feet that may be painful and shows clear boundaries at the joints 1
• These changes are characterized by their sharp demarcation rather than gradual fading 1

Convalescent Phase (2-3 weeks after onset):

• Membranous desquamation starting in the periungual region of fingers and toes 1
• This peeling typically occurs when fever has already resolved 1

Critical Distinguishing Features

What the rash is NOT:

• No bullous or vesicular lesions (their presence excludes Kawasaki disease) 1
• No exudative features 1
• Not discrete focal lesions 1

Diagnostic Context for a 1-Year-Old

This age group requires heightened vigilance because:

• Incomplete Kawasaki disease is more common in infants under 1 year, who may present with fewer than 4 of the 5 principal features 1, 3, 4
• Coronary artery aneurysm risk is paradoxically higher in this age group if untreated (up to 25% without treatment) 3, 5
• The diagnosis requires fever ≥5 days plus ≥4 of 5 principal features: polymorphous exanthem, bilateral conjunctival injection, oral/lip changes, extremity changes, and cervical lymphadenopathy 1, 4

Common Diagnostic Pitfalls

• Do not wait for all clinical features to appear simultaneously—they often evolve sequentially, requiring careful review of the entire clinical course 4
• Do not dismiss Kawasaki disease if the rash is subtle or atypical—incomplete presentations are the rule rather than exception in 1-year-olds 1, 3
• Perineal involvement with early desquamation is a particularly helpful diagnostic clue that may precede other features 2
• If fever persists ≥5 days with only 2-3 features (including rash), immediately measure ESR and CRP—if ESR ≥40 mm/hr or CRP ≥3 mg/dL, proceed with full Kawasaki workup including echocardiography 3, 4

Clinical Urgency

Early recognition is critical: Treatment with IVIG within 10 days of fever onset reduces coronary artery abnormality risk from 25% to approximately 5%. 4, 5 In a 1-year-old with prolonged fever and any combination of rash and other Kawasaki features, maintain a low threshold for echocardiography and subspecialty consultation. 1, 4