What is the differential diagnosis for a rash on the cheeks of an infant?

Differential Diagnosis of Cheek Rash in Infants

The most common causes of cheek rash in infants are atopic dermatitis, seborrheic dermatitis, and erythema infectiosum (fifth disease), with atopic dermatitis being the most frequent diagnosis in this age group. 1, 2

Primary Differential Diagnoses

Atopic Dermatitis (Most Common)

• Infants typically present with lesions starting on the cheeks and extending over time to the neck, trunk, and extensor surfaces of extremities, with notable sparing of the diaper area. 1
• Diagnosis requires pruritus with symmetrical distribution, eczema, and chronic/relapsing course (>2 months in infancy). 1
• Acute lesions appear as erythema, exudation, papules, and vesiculopapules, while chronic lesions show lichenification, prurigo, scales, and crusts. 1, 2
• Personal or family history of atopy (asthma, hay fever, allergic rhinitis) strongly supports the diagnosis. 1
• Dry skin (xerosis) is a characteristic feature that helps distinguish it from other conditions. 2

Seborrheic Dermatitis

• Difficult to separate from atopic dermatitis in infancy, and the two conditions may overlap in this age group. 1
• Unlike atopic dermatitis, seborrheic dermatitis affects the groin and axillary regions and tends not to be pruritic. 1
• Presents with greasy, yellowish scaling on the scalp (cradle cap) that can extend to the face including cheeks. 3
• Typically self-limited and resolves with shampooing and gentle scale removal. 3

Erythema Infectiosum (Fifth Disease)

• Characterized by the classic "slapped cheek" appearance—bright red facial rash on the cheeks. 4
• Preceded by a viral prodrome with low-grade fever and malaise. 4
• The facial rash is followed by a lacy, reticular rash on the trunk and extremities. 4

Critical "Cannot Miss" Diagnoses

Eczema Herpeticum (Medical Emergency)

• Presents as multiple uniform "punched-out" erosions or vesiculopustular eruptions superimposed on atopic dermatitis. 5, 2
• Requires immediate systemic acyclovir treatment as this is a dermatologic emergency. 6, 5
• Any deterioration of eczema with vesicular lesions mandates urgent evaluation and antiviral treatment. 6, 7

Secondary Bacterial Infection

• Suspect when there are signs of crusting, weeping, honey-colored discharge, or erosions. 6, 7
• Staphylococcus aureus superinfection is common in atopic dermatitis patients. 2
• Requires empirical antibiotics covering S. aureus or Streptococcus (cephalexin or flucloxacillin). 6, 7

Kawasaki Disease (Incomplete Presentation)

• Infants <6 months may present with prolonged fever and subtle clinical signs, making diagnosis challenging. 1
• Nonpurulent conjunctivitis, oral mucosal changes, and rash (including facial involvement) are key features. 1
• Consider in any infant with fever ≥7 days, laboratory evidence of systemic inflammation, and no other explanation. 1
• High index of suspicion is critical as infants are at substantial risk for coronary artery abnormalities. 1

Diagnostic Approach

Essential History Elements

• Age of onset (before 6 months suggests congenital atopic dermatitis or mastocytosis). 6, 7
• Presence and severity of pruritus (mandatory criterion for atopic dermatitis). 1, 7
• Distribution pattern and progression of lesions over time. 6, 7
• Family history of atopic diseases (asthma, hay fever, eczema). 1, 7
• Duration of fever if present (≥5-7 days raises concern for Kawasaki disease). 1
• Exposure to irritants, recent viral illness, or sick contacts. 4

Physical Examination Priorities

• Assess whether the diaper area is spared (typical of atopic dermatitis) or involved (suggests seborrheic dermatitis or Candida). 1
• Look for uniform "punched-out" erosions suggesting eczema herpeticum. 6, 5
• Check for honey-colored crusting or weeping indicating bacterial superinfection. 6, 7
• Examine for dry skin and involvement of extensor surfaces (atopic dermatitis pattern in infants). 1, 2
• Evaluate for conjunctivitis, oral mucosal changes, and lymphadenopathy if fever is present (Kawasaki disease). 1
• Assess for the "slapped cheek" appearance characteristic of erythema infectiosum. 4

Laboratory Evaluation (When Indicated)

• Laboratory testing is not required for straightforward atopic dermatitis diagnosis. 1
• If Kawasaki disease is suspected: obtain CBC, CRP, ESR, albumin, ALT, urinalysis, and echocardiography. 1
• Viral or bacterial cultures if secondary infection is suspected. 2
• Elevated IgE levels are present in 80% of atopic dermatitis cases but are not diagnostic. 1

Initial Management Algorithm

If Vesicular/Erosive Lesions Present

• Rule out eczema herpeticum immediately and start systemic acyclovir urgently. 6, 5
• Perform Tzanck smear or viral culture to confirm herpes simplex virus. 7

If Honey-Colored Crusting or Weeping Present

• Add empirical antibiotics for bacterial superinfection (cephalexin or flucloxacillin). 6, 7
• Consider bacterial culture to guide antibiotic selection. 2

If Chronic, Pruritic with Dry Skin

• Treat as atopic dermatitis with frequent emollient application (cornerstone of therapy). 1, 6
• Apply low-potency topical corticosteroids (hydrocortisone) for active flares. 1, 6
• Avoid irritants and triggers (harsh soaps, rough fabrics, temperature extremes). 1
• Apply emollients immediately after 10-15 minute lukewarm baths. 1

If Fever ≥5-7 Days with Rash

• Evaluate for incomplete Kawasaki disease, especially in infants <6 months. 1
• Obtain inflammatory markers (CRP, ESR) and echocardiography if clinical suspicion is high. 1

Common Pitfalls to Avoid

• Never miss eczema herpeticum—any deterioration of eczema with vesicular lesions requires urgent antiviral treatment. 6, 5
• Do not mistake rash and mucosal changes following antibiotic treatment for drug reaction when Kawasaki disease is the actual diagnosis. 1
• Avoid attributing all facial rashes in infants to "baby acne" without considering atopic dermatitis or seborrheic dermatitis. 3
• Do not overlook bacterial superinfection in atopic dermatitis, which can lead to treatment failure. 5, 2
• Reassess in 1-2 weeks if no improvement with initial therapy, and consider dermatology referral if diagnosis remains uncertain. 6
• Recognize that infants <6 months with Kawasaki disease may present with fever and minimal other findings, requiring high clinical suspicion. 1