What is the most likely diagnosis for a 2-year-old female patient presenting with a rash and pruritus on the face, body, and extensor surfaces?

Diagnosis: Atopic Dermatitis

The diagnosis is atopic dermatitis (A), not seborrheic dermatitis, based on the characteristic presentation of pruritus with rash on the face, body, and extensor surfaces in a 2-year-old child. 1, 2

Key Diagnostic Features Supporting Atopic Dermatitis

Age-Specific Distribution Pattern

• In infancy and early childhood (which includes this 2-year-old), atopic dermatitis characteristically starts on the cheeks and extends to the neck, trunk, and extensor surfaces of extremities—exactly matching this patient's presentation 1, 2, 3
• This extensor surface involvement is the hallmark pattern for this age group, before the typical transition to flexural involvement that occurs after age 2-4 years 2, 4

Pruritus as a Mandatory Criterion

• Pruritus is an essential diagnostic criterion for atopic dermatitis at any age—the patient's presenting complaint of pruritus strongly supports this diagnosis 1, 3
• Pruritus is considered a mandatory feature that must be present for diagnosis according to multiple international guidelines 1

Why Not Seborrheic Dermatitis

Seborrheic dermatitis is excluded by several critical distinguishing features:

• Absence of pruritus: Seborrheic dermatitis characteristically lacks significant itching, whereas this patient presents with pruritus as a chief complaint 3
• Lesion morphology: Seborrheic dermatitis presents with greasy, yellow scales, not the red, scaly, pruritic lesions described here 3
• Distribution pattern: Seborrheic dermatitis affects the groin and axillary regions, while atopic dermatitis spares these areas—the extensor surface involvement is classic for atopic dermatitis, not seborrheic dermatitis 3

Diagnostic Criteria Fulfilled

This patient meets all three essential TAPAAI diagnostic criteria for pediatric atopic dermatitis 1:

1. Pruritus with age-specific distribution pattern (face, body, extensor surfaces) 1, 3
2. Eczematous lesions with the characteristic infantile pattern 1, 2
3. Chronic or relapsing course (>2 months for children under 12 months, >6 months for older children) 1

Clinical Pitfalls to Avoid

• Do not confuse the age-specific distribution patterns: extensor involvement is typical for infants/toddlers, while flexural involvement develops later in childhood 2, 4
• While seborrheic dermatitis and atopic dermatitis can overlap in infancy, the presence of significant pruritus and extensor surface involvement strongly favors atopic dermatitis 3
• Consider secondary bacterial infection if crusting or weeping is present, as Staphylococcus aureus superinfection is common in atopic dermatitis 1, 2
• Rule out scabies (look for burrows in finger webs) and immunodeficiency states (check for recurrent infections) in the differential diagnosis 1, 2