palmoplantar keratoderma There are often characteristic islands of sparing ( Fig 70.8 ) It is most often confused with psoriasis, which it can closely resemble, but PRP lesions lack the overlying silvery scale of psoriasis PRP is often idiopathic and sporadic in its occurrence PRP can occur as a postinfectious process (most commonly streptococcal and occasionally HIV), as an adverse drug reaction, and in adults, as a paraneoplastic phenomenon associated with a variety of malignancies The condition has also been associated with CARD mutations and autosomal dominant inheritance (early-onset form) Long-term treatments include use of emollients, topical corticosteroids, topical retinoids, vitamin D analogs, topical calcineurin inhibitors, and systemic agents such as phototherapy and biologic agents (infliximab, ustekinumab, etanercept, adalimumab) FIGURE 70.8 Pityriasis rubra pilaris Note the orange or salmon-colored appearance of the papules In the emergency department, identification of an affected child should include evaluation for possible infectious triggers and treatment for any active infections Referral to a dermatologist is recommended to institute longer-term treatment as needed Pityriasis lichenoides Pityriasis lichenoides is a lymphocytic inflammatory skin condition that classically has been divided into the acute (pityriasis lichenoides et varioliformis acuta or PLEVA) form and the chronic (pityriasis lichenoides chronica or PLC) form This distinction may be artificial as there are often overlapping features of both in an individual patient so the term pityriasis lichenoides (PL) is generally preferred There is a rare and severe form known as febrile ulceronecrotic Mucha–Habermann (FUMH) syndrome Patients present with persistent crops of skin lesions that vary in appearance from crusted vesicles and papules ( Fig 70.9 ) to scaly patches and small plaques that may be hypopigmented in some cases ( Fig 70.10 ) These lesions are most often asymptomatic There is often a predilection for sun-protected areas, and in summertime, areas exposed to sunlight often show fewer skin lesions In FUMH syndrome, these lesions are often accompanied by fever and larger, often painful, ulcerated papules and plaques At times, the condition may be initially misdiagnosed as varicella, but PL patients are generally afebrile (except in FUMH), and the lesions of PL persist for months to years At other times, the condition may resemble PR but PL will persist for months to years, differentiating it from PR Infants who develop crusted papular eruptions that resemble PL should also be evaluated for the possibility of LCH FIGURE 70.9 Crusted papules of pityriasis lichenoides et varioliformis acuta ... 70.8 Pityriasis rubra pilaris Note the orange or salmon-colored appearance of the papules In the emergency department, identification of an affected child should include evaluation for possible