ABSTRACT
The clinical spectrum of phenylketonuria, an autosomal recessive deficiency of phenylalanine hydroxylase, includes an eczematous condition in 20–40% of untreated patients that resembles atopic dermatitis (AD). The most common disorders confused with infantile/childhood AD are infantile seborrheic dermatitis, psoriasis, contact dermatitis, and scabies. The severe pruritus associated with scabetic infestation often evokes a diagnosis of AD, but the two conditions can usually be differentiated based on history and physical examination. The diagnosis of AD is usually straightforward but atypical features should prompt the clinician to explore alternatives. Infants and young children with AD develop an accentuation of the infraorbital folds or pleats, called Dennie–Morgan folds, associated with lower eyelid eczema. Pityriasis lichenoides chronica is a rare mimicker of AD. Although dyshidrotic eczema typically occurs independently, it may occur in patients with AD. As in children, dermatophyte infections in adults mimic AD.
