Small, Scaly Lesions

Fig. 5.1 Guttate psoriasis. Lesions in (A) developed after a sunburn (Koebner phenomenon). A, Courtesy, Ronald Rapini, MD. A, From Bolognia JL, Jorizzo JL, Schaffer JV. Dermatology, 3e. London: Saunders, 2012, with permission.

Fig. 5.2 Guttate psoriasis. Mounds of parakeratosis, often with neutrophils.

Histopathology:

Slight acanthosis and mounds of parakeratosis that often contain neutrophils (arrow; Fig. 5.2)

Dilated papillary dermal vessels may be present (circles; see Fig. 5.2)

Pityriasis Rosea

Classically starts with a herald patch (often the largest lesion)

• Precedes development of a widespread, symmetric eruption (see below)

Once well developed, widespread and symmetric (Fig. 5.3)

• Proximal extremities and trunk

• Follow Langer’s lines, forming a “Christmas tree” pattern on the back

Fine white central scale (arrow) with collarettes overlying round to oval thin salmon-colored (circle) papules/plaques (Figs 5.4, 5.5)

Fig. 5.3 Pityriasis rosea. The typical distribution, with lesions oriented with long axes parallel to the red lines (Langer’s lines). From Bolognia JL, Schaffer JV, Duncan KO, Ko CJ. Dermatology Essentials, 1e. Philadelphia: Saunders, 2014, with permission.

Fig. 5.4 Pityriasis rosea. From James WD, Berger T, Elston D. Andrews’ Diseases of the Skin, 11e. Edinburgh: Saunders, 2011.

Fig. 5.5 Pityriasis rosea. A, Courtesy, Yale Dermatology Residents’ Slide Collection. A,B, From Bolognia JL, Jorizzo JL, Schaffer JV. Dermatology, 3e. London: Saunders, 2012, with permission.

Histopathology:

Mounds of parakeratosis (arrow; see Fig. 5.5), generally without neutrophils

Mild spongiosis, mild perivascular lymphocytic infiltrate with extravasated erythrocytes (circle; see Fig. 5.5)

Pityriasis Rosea – Variants

Inverse (Fig. 5.6A)

• Tends to affect body folds (axillae, groin)

• Long axis of lesions along Langer’s lines (see Fig. 5.3)

Fig. 5.6 Pityriasis rosea. A Inverse pityriasis rosea. B Pityriasis rosea in dark skin. A, Courtesy, Yale Dermatology Residents’ Slide Collection. B, Courtesy, Aisha Sethi, MD. B, From Bolognia JL, Schaffer JV, Duncan KO, Ko CJ. Dermatology Essentials, 1e. Philadelphia: Saunders, 2014, with permission.

In Pigmented Skin (Fig. 5.6B)

• May have follicular prominence

• May be hyperpigmented centrally

Lichen Planus

Often Symmetric

• Classically on the wrists/forearms, ankles/shins, dorsal hands/feet, genital area (Fig. 5.7)

• May be more generalized

Flat-topped violaceous (circle) papules/plaques (Figs 5.8, 5.9A)

Fig. 5.7 Lichen planus, typical distribution.

Fig. 5.8 Lichen planus. From Schwarzenberger K, Werchniak AE, Ko C. General Dermatology. London: Saunders, 2009.

Fig. 5.9 Lichen planus. Flat-topped pink to purplish papules with adherent scale. There is hyperkeratosis, hypergranulosis, and lichenoid inflammation. A,B, Courtesy, Yale Dermatology Residents’ Slide Collection.

Classic scale is interconnecting white lines (Wickham’s striae) (arrow), possibly corresponding to hyperkeratosis/hypergranulosis (arrow) (Figs 5.9, 5.10)