Porth's Essentials of Pathophysiology, 4e

1165

Disorders of Skin Integrity and Function

C h a p t e r 4 6

reserved for treatment of thick chronic plaques that do not respond to less-potent preparations. Although the corticosteroids are rapidly effective in the treatment of psoriasis, they are associated with flare-ups after dis- continuation and they have many potential side effects. Their effectiveness is increased when used under occlu- sive dressings, but there is an increase in side effects. Systemic treatments include phototherapy, photoche- motherapy, methotrexate, corticosteroids, and cyclo- sporine. The positive effects of sunlight have long been established. Phototherapy with UVB radiation is a widely used treatment. Newly developed narrow-band UVB radiation is reportedly more effective than broad-band UVB. 39 Photochemotherapy involves using a light-acti- vated form of the drug methoxsalen. Methoxsalen, a pso- ralen or phototoxic drug, exerts its actions when exposed to UVA radiation in 320- to 400-nm wavelengths. The combination treatment regimen of psoralen and UVA is known by the acronym PUVA . Methoxsalen is given orally before UVA exposure. Activated by the UVA energy, methoxsalen inhibits DNA synthesis, thereby preventing cell mitosis and decreasing the hyperkeratosis that occurs with psoriasis. Although viewed as one of the safest therapies since its introduction in the 1970s, PUVA increases the risk for squamous cell carcinoma, and it may increase the risk for development of melanoma. Methotrexate, which is used for cancer treatment, is an antimetabolite that inhibits DNA synthesis and pre- vents cell mitosis. Oral methotrexate has been effective in treating psoriasis when other approaches have failed. The drug has many side effects, including nausea, mal- aise, leukopenia, thrombocytopenia, and liver function abnormalities. Cyclosporine is a potent immunosuppres- sive drug used to prevent rejection of organ transplants. It suppresses inflammation and the proliferation of T cells in persons with psoriasis. Its use is limited to severe psoriasis because of serious side effects, including neph- rotoxicity, hypertension, and increased risk of cancers. Intralesional cyclosporine also has been effective. Biologic agents (drugs that are taken from or made of living tissues or cells instead of chemicals) that target the activity of T lymphocytes and cytokines responsible for the inflam- matory nature of psoriasis have proven effective. 41 Pityriasis Rosea Pityriasis rosea is a rash that primarily affects children and young adults. The origin of the rash is unknown, but is thought to be caused by an infective agent, possibly a herpesvirus. 42 Its incidence is highest in winter. Cases occur in clusters and among persons who are in close contact; however, there are no data to support commu- nicability, suggesting it may be an immune response to any number of agents. The characteristic lesion is an oval macule or papule with surrounding erythema (Fig. 46-17). The lesion spreads with central clearing, much like tinea corporis. This initial lesion is called the herald patch and is usually on the trunk or neck. As the lesion enlarges and begins to fade (2 to 10 days), successive crops of lesions appear on the trunk and neck. The lesions on the back have a characteristic

Treatment. The goals for psoriasis treatment focus on suppressing the hyperkeratosis, epidermal inflamma- tion, and abnormal keratinocyte differentiation that are characteristic of the disease. Usually, topical agents are used first in any treatment regimen and when less than 20% of the body surface is involved. They include emollients, keratolytic agents, coal tar products, corti- costeroids, and calcipotriene. 39 Emollients hydrate and soften the psoriatic plaques. Keratolytic agents are peel- ing agents that soften and remove plaques. Salicylic acid is the most widely used. Coal tar, the by-product of the processing of coke and gas from coal, is one of the oldest yet most effective forms of treatment. The exact mechanism of action of tar products is unknown, but side effects of the treatment are few. Newer preparations of coal tar lotions and shampoos are more aesthetically pleasing, but the odor remains a problem. Calcipotriene (a vitamin D derivative) ointment has been shown to inhibit epidermal cell proliferation and enhance cell differentiation. Tazarotene, a synthetic retinoid, also has been effective, but it is teratogenic and should be avoided in women of childbearing age. Topical corticosteroids are widely used and relatively effective. They are generally more acceptable because they do not stain and are easy to use. Low-potency preparations usually are used on the face and on areas of the body, such as the groin and axilla, where the skin tends to be thinner. High-potency preparations are FIGURE 46-16. Psoriasis of the elbow. Note the irregular red patches covered by a dry scaly hyperkeratotic stratum corneum. (From the Centers for Disease Control and Prevention Public Health Image Library. No. 4055. Courtesy of Susan Lindsley.)