Key Clinical Questions
When should a patient with an erythematous scaly eruption be evaluated for an underlying infectious process?
How should the patient with diffuse erythroderma be evaluated?
What are the best topical treatments for psoriasis?
Are oral steroids useful in the treatment of psoriasis?
Are there physical findings that help differentiate between contact and irritant dermatitis?
Papulosquamous disorders are a group of unrelated dermatologic conditions in which patients present with red, raised lesions with scale. While psoriasis is the prototypical papulosquamous disorder, similar skin lesions may be seen in infections, lymphomas, and allergic conditions. The conditions described in this chapter are ubiquitous, and primarily inflammatory in nature. From a clinical point of view, the history, the distribution of the lesions, and careful evaluation of the primary lesion are most helpful in helping establish the diagnosis. Ancillary tests include a KOH preparation, a skin biopsy and, if necessary, dermatologic consultation. It should be remembered that treating a condition without a definitive diagnosis can lead to unnecessary patient aggravation and added expense.
Psoriasis, a chronic relapsing condition with genetic and environmental triggers, can be readily diagnosed on skin examination. It is very common. Approximately 2% of the population is affected by psoriasis. In the United States, the prevalence may be as high as 4.6%.
Psoriasis was formerly likened to “wound healing gone wrong.” It was blamed on abnormally rapid keratinocyte growth and maturation, with a reduction of the epidermal turnover time from the normal 4 weeks to only 3 to 4 days. However, psoriasis is now recognized to be a T-cell–mediated disease. Several T helper lymphocyte-associated cytokines drive epidermal proliferation, such as interferon-α, tumor necrosis factor, and certain interleukins, particularly IL-17. Circulating levels of IL-22 are especially correlated with disease activity. Biopsy reveals epidermal hyperplasia with tortuous papillary dermal blood vessels, and a loss of the granular layer with abundant parakeratotic scale. In pustular lesions, neutrophils form collections in the epidermis.
The lesions are well demarcated and associated with a characteristic silvery white, plate-like adherent scale (Figure 146-1).
Chronic plaque psoriasis with classic scale.
When the thick scale is forcibly removed, small punctate bleeding points develop (the Auspitz sign) (Figure 146-2).
Chronic plaque psoriasis with Auspitz sign.
Psoriasis may affect the entire body surface, including the nails. As injury can trigger psoriasis, lesions are typically seen on the elbows, knees, and buttocks (Figure 146-3).
Jockey with worsening psoriasis in areas of trauma.