Case: On bilateral knees of a 14-month-old male infant, there are thin erythematous pale pink plaques. His past medical history is noncontributory.
The patient is otherwise healthy. He has reached developmental milestones and started crawling at 6 months old. The eruption is only present on the knees and is asymptomatic. There is no dermatographism or exacerbation with heat or trauma. The individual lesions coalesce to form plaques.
A. Atopic dermatitis
B. Juvenile dermatomyositis
C. Juvenile rheumatoid arthritis (Still's disease)
D. Frictional lichenoid dermatosis
Answer: D. Frictional lichenoid dermatoses. These thin plaques on the knees are from crawling, which may occur in infants in areas that are in contact with the ground. Although it resembles rashes that accompany systemic illness, it is a benign condition that resolves once the infant outgrows crawling stage.
Frictional lichenoid dermatitis (frictional lichenoid eruption, juvenile papular dermatitis) is a cutaneous disorder affecting children, especially boys. Most cases are seen in the spring and summer when outdoor activities are common, and many cases have been associated with playing in sandboxes (sandbox dermatitis) or on grass (Paller & Mancinie, 2011).
Approximately half of the affected children have atopic dermatitis, allergic rhinitis, or asthma. The eruption is characterized by aggregates of discrete lichenoid papules, 1 or 2 mm in diameter, which occur primarily on the elbows, knees, and backs of the hands of children in whom such areas are subject to minor frictional trauma without protection of clothing. Lesions may be hypopigmented, and associated pruritus is often severe but may be absent (Paller & Mancinie, 2011).
This can be confused with onset of a systemic disease that can be characterized by a similar pale pink macular rash in juvenile rheumatoid arthritis (Still's disease). However, Still's disease includes recurrent high fevers and arthritis along with the urticarial and pruritic rash with marked dermatographism (Mason & Reed, 2005). This rash is brought out by heat or minor trauma, known as Koebner phenomenon.
Cutaneous lesions of juvenile dermatomyositis may be extremely pruritic. They are exacerbated by sunlight and can precede muscle diseases by several weeks to 4 years. Scalp lesions are common in most patients (Feldman, Rider, Reed, & Pachman, 2008).
Atopic dermatitis is most common in infants and may start as early as 2-6 months. In children younger than 2 years old, skin lesions begin on the face, scalp, hands, and feet. The rash is often itchy. In older children, the rash is more often seen on inside of the knees and elbows, although the rash can occur anywhere on the body during severe cases. Intense itching is common (James, Berger, & Elston, 2011).
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