up 18%, and the genitalia make up 1%. BSA involvement of <3% is considered mild, 3% to 10% is moderate, and >10% is severe disease. BSA is a component of the Psoriasis Area Severity Index (PASI), which also includes 4-point rating scales for erythema, induration, and flaking. Payers often require PASI scores before authorizing payment for newer, more expensive medications. However, PASI scores should not be the sole assessment of disease severity. Other important factors are involvement of sites that are difficult to treat topically (face, scalp, folds, groin, nails), arthritis, and psychometric symptoms such as social withdrawal.32,45 The Children's Dermatology Life Quality Index (CDLQI) is a validated, easily usable tool for clinical experience and psychometric properties of PsO in pediatric patients age four years to 15 years and 11 months.46 CDLQI may be used to evaluate pediatric patients' health-related quality of life (HRQOL) and considered along with PASI scores to determine the overall burden of disease in this age group. In fact, the Joint American Academy of Dermatology-National Psoriasis Foundation (AAD-NPF) guidelines recommend that both BSA and CDLQI be used as a measure of PsO severity.45
Differences Between Pediatric and Adult PsO
Children may be at higher risk for missed and/or delayed diagnosis compared with adults. The key clinical differences that distinguish childhood-onset PsO from that in adults include lesion morphology, sites of predilection, and disease burden. Plaques in children can be less indurated and the scale finer without the classic silvery quality.7 Isolated involvement of the ear canals in children may be confused with otitis externa.11 Eyelid margins are another site of predilection that can be isolated and mistaken for other forms of blepharitis.19 Pruritus may often be present.
Differential Diagnosis of Pediatric PsO
Diagnosing pediatric PsO can be challenging for pediatricians, as the signs may appear similar to eczema, tinea, or other inflammatory skin conditions (Table 2). Pediatric PsO is not commonly associated with asthma or allergic rhinitis, whereas these are frequently found in patients with AD or members of their family. Both pediatric PsO and AD feature erythema, induration, and scale, and both respond to treatment with topical corticosteroids, but PsO is more likely to rebound with treatment discontinuation.47 Eczema is often most prominent in the antecubital and popliteal fossae, flexor wrists, and dorsal aspects of the hands, while pediatric PsO lesions commonly localize to the scalp, palms, soles, and extensor surfaces of the elbows and knees.47 Furthermore, eczema typically spares the diaper area and skinfolds, while PsO commonly involves this area. Nail involvement is another feature of pediatric PsO that can support differentiation from eczema,47 although nail pits and dystrophy can occur in eczema, especially in the setting of paronychia. Misdiagnosis of pediatric PsO as eczema is also likely related to the higher frequency of eczema compared with PsO. Lesional skin biopsy can help distinguish pediatric PsO from other skin conditions.11 Diagnostic histologic features include epidermal thickening with elongated rete ridges, hypergranulosis, and parakeratosis, but clinically atypical pediatric PsO is less likely to exhibit psoriatic histology. The histologic features of pediatric PsO have been reported in 57.6% of infants with this suspected diagnosis.48 The inflammatory impact on pigmentation is
