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important ones. Linear lesions can also be seen with allergic contact
dermatitis and inoculation sites for warts or molluscum.
The distribution of skin lesions may also provide useful diagnostic clues.
Plaque-type psoriasis favors the extensor surfaces of the extremities like the
elbows and knees, as well as the scalp, ears, and intertriginous areas. While
seborrheic dermatitis also tends to involve intertriginous areas, it has a
predilection for the perinasal areas, eyebrows, and external auditory canals.
PR usually manifests predominantly on the torso, and skin lesions are
characteristically distributed along skin tension lines (the lines of Langer)
producing the so-called “fir tree” or “pine tree” pattern on the back.
Concomitant involvement of the diaper area, acral areas, and the face would
raise the possibility of seborrheic dermatitis, acquired zinc deficiency, or
acrodermatitis enteropathica.
Examination of the mucous membranes and skin appendages can provide
corroborating evidence for a particular diagnosis. Geographic tongue may be
a normal variant but is often a feature of psoriasis. Oral erosions or lacy
white patterns in the mouth suggest lichen planus. Genital involvement is
also a typical feature of psoriasis, lichen planus, lichen nitidus, and syphilis.
Nail pitting is frequently seen in psoriasis, but nails are generally normal in
PRP.
The degree of pruritus is a helpful differentiating symptom for
papulosquamous disorders. Many of the papulosquamous disorders are not
particularly pruritic. When intense, itching suggests lichen planus or
lichenoid drug eruptions ( Table 70.1 ).

Psoriasis
Psoriasis is a relatively common, chronic papulosquamous disease that
makes up approximately 4% of all skin disorders encountered in children.
There is a predisposition for involvement of the scalp, perineum (particularly
in infants), and the extensor surfaces of the body, particularly the elbows and
knees. Psoriatic arthritis occurs in a minority of patients, but arthritis is more

common among pediatric patients. One-third of adults with psoriasis
experiences onset of disease in childhood or adolescence. Among children
with psoriasis, the majority develop the condition during adolescence
although the condition arises in 12% before the age of 10 years.


Psoriasis occurs in several forms during childhood: plaque-type, guttate,
palmoplantar, inverse, pustular, and erythrodermic. The most classic form is
plaque-type psoriasis which is associated with thick, beefy red plaques with
overlying silvery scales ( Fig. 70.2 ) often in a symmetrical distribution on
the extensor surfaces of the extremities, although other anatomic sites may
be affected. When a scale is removed, there may be pinpoint areas of
bleeding (Auspitz sign). Guttate psoriasis is one of the most common forms
encountered in childhood, manifesting as guttate (drop-like) erythematous
scaly papules scattered over the body ( Fig. 70.3 ). The characteristic silvery
scale is only minimally expressed, and the lesions may appear quite red. This
form is classically (but not always) preceded by or coincides with a
streptococcal infection.
Palmoplantar psoriasis manifests as thickened plaques concentrated on the
palms and soles of the feet ( Fig. 70.4 ). The plaques may become fissured
and painful. These areas may become so thickened that patients complain of
pain with moving the fingers or walking.
Inverse psoriasis refers to the usually pink, salmon-colored, sometimes
macerated plaques that arise in the axillae, inguinal areas, or on the genitalia
and buttocks ( Fig. 70.5 ). The gluteal crease is usually involved.
Erythrodermic psoriasis is less common and more severe. Onset may be
abrupt or gradual, with a diffuse erythema and severe desquamation. In the
growing child, there may be associated failure to thrive.

FIGURE 70.1 Note the linear purplish plaque consistent with koebnerization of lichen
planus.

Pustular psoriasis is rarely seen in children and may arise suddenly.
Patients may have other forms of psoriasis that then suddenly transition into
pustular psoriasis flares, occasionally triggered by use of or withdrawal of
systemic corticosteroid therapy. Various sizes of sterile and superficial
pustules develop on an erythrodermic background. Avoidance of systemic
steroids may be prudent in patients with psoriasis since withdrawal can
precipitate pustular flares of the disease.
Characteristically small, pitted lesions are seen on the nails in 25% to 50%
of patients in all forms of the condition. Areas resembling tan-brown oil
spots may appear as well within the nails.
Eighty percent of children have scalp involvement, and patients with early
scalp psoriasis may be mistaken for having tinea capitis. In contrast to tinea
capitis, most cases of psoriatic scalp involvement do not show frank hair loss
or hair breakage, and scalp lymphadenopathy in psoriasis is uncommon.


TABLE 70.1
CLINICAL FEATURES OF PAPULOSQUAMOUS DISORDERS