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There are many conditions that can have truncal involvement. This section focuses on some common eruptions that frequently affect the trunk: scaling macules, papules, and plaques; morbilliform or urticarial eruptions; blistering disorders; insect bites; and two miscellaneous disorders, molluscum contagiosum and Kaposi sarcoma (KS). Although the location can be helpful, the clinical appearance of the lesions and overall assessment of the patient are needed to make the correct diagnosis.

Scaling conditions include psoriasis, seborrheic dermatitis, tinea corporis, pityriasis (“tinea”) versicolor, eczema/atopic dermatitis, lichen planus, secondary syphilis, and scabies. Table 249-1 lists common features distinguishing these eruptions.

Table 249-1 Comparison Features of Common Papulosquamous Eruptions


Psoriasis is a common disorder that affects 1.5% to 2.0% of the population. It is uncommon in West Africans and Japanese, and very rare in American Indians. It has equal incidence in males and females. Psoriasis is associated with a hereditary predisposition. When one parent has the disease, there is an 8% incidence in the offspring, and if psoriasis is present in both parents, there is >40% chance that the child will have the condition. The peak incidence is in the early 20s with an insidious onset. Explosive eruptions can be seen following streptococcal pharyngitis, severe sunburn, or in patients with acquired immunodeficiency syndrome (AIDS). Stress or alcohol ingestion ...

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