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Papulosquamous disorders present with papules or plaques, and with scales. Diseases in this group include psoriasis, parapsoriasis, pityriasis lichenoides, pityriasis rosea, pityriasis rubra pilaris, lichen planus, secondary syphilis, and lichen amyloidosis.


Psoriasis is a chronic immune-mediated inflammatory disease typically characterized by the presence of well-demarcated plaques with overlying silvery scales (Figures 4–1, 4–2, 4–3, 4–4, 4–5, 4–6, 4–7, 4–8, 4–9, 4–10, 4–11, 4–12, 4–13, 4–14, 4–15, 4–16, 4–17, 4–18, 4–19, 4–20, 4–21, 4–22, 4–23, 4–24, 4–25, 4–26, 4–27, 4–28, 4–29, 4–30). It is estimated to affect between 0.1% and 3% of the population. Studies on the disease show that the prevalence of psoriasis in Asian countries range from 0.19% in Taiwan to 0.47% in China.

Figure 4-1

Plaque-type psoriasis

Well-demarcated pink plaques with variable amount of scaling are seen in chronic plaque psoriasis. Due to the Koebner phenomenon, there is a tendency to involve areas prone to trauma such as the elbows or knees. Gross hyperkeratosis can develop if lesions are not treated.

Figure 4-2

Plaque-type psoriasis

Small, pink, scaly plaques may coalesce to form larger plaques, which sometimes have annular or gyrate configurations.

Figure 4-3

Plaque-type psoriasis

More extensive psoriasis lesions with involvement of the trunk should prompt consideration of treatment with systemic medication or phototherapy if topical treatments fail.

Figure 4-4

Plaque-type psoriasis—histology

In chronic plaque psoriasis, histology shows confluent parakeratosis, the presence of intracorneal and subcorneal collections of neutrophils, regular psoriasiform epidermal hyperplasia with hypogranulosis, and suprapapillary thinning. Capillaries in the papillary dermis are dilated, and there is a superficial perivascular infiltrate often comprising a mixture of neutrophils and lymphocytes.

Figure 4-5

Plaque-type psoriasis—histology

A typical feature of psoriasis is the presence of collections of neutrophils (Munro’s microabscesses) within the stratum corneum and neutrophil entrapment in the parakeratotic scale. Also illustrated here is the formation of spongiform pustules in the upper layers of the epidermis.

Figure 4-6

Guttate psoriasis

The small discrete papules and plaques of guttate psoriasis are usually distributed throughout the body, particularly on the trunk. Guttate psoriasis tends to involve children or young adults and there may be a preceding acute streptococcal infection. In a patient with dark skin, the lesions may resolve with significant post-inflammatory hyper- or hypopigmentation.

Figure 4-7

Koebner phenomenon

Psoriasis lesions ...

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