PSORIASIS.Psoriasis is a common cause of peristomal skin disease because it may appear in irritated or traumatized skin (Koebnersphenomenon) and because it is associated with inflammatory bowel disease (Chapter 18). Peristomal psoriasis presents as aglazed erythema similar to flexural psoriasis (eFig. 97-9.3 in online edition) and can be treated in the same way with topicalcorticosteroids although, at the peristomal site, a nongreasy base should be selected (Table 97-1). The diagnosis is usuallyunmistakable being part of more generalized involvement (eFig. 97-9.4 in online edition) but localized peristomal involvementis described.21 Resolution of psoriasis under hydrocolloid occlusion has been described,22 which is of relevance to stomapatients because 50% of cases of peristomal psoriasis will resolve if a bag is selected with a thicker, hydrocolloid-onlybarrier. Where the patient can tolerate the stoma being temporarily unprotected from leaks, ultraviolet (UV) phototherapy iseffective as for psoriasis elsewhere. The mucous membranes of the stoma should be protected from UV light. Althoughirritating topical psoriasis treatments are not usually tolerated, some patients have had success with creams containinghydrocortisone 1% and coal tar 3%, the application being left on the skin for 1 hour each day (Table 97-1, Point 3).Superficial X-ray (Grenz-ray) therapy has been used in recalcitrant casesFitzpatricks 1574

POLYCYCLIC AROMATIC HYDROCARBONS.Exposure to polycyclic aromatic hydrocarbons (PAHs) accounts for most of the reported occupational skin tumors.122 PAHsare hydrophobic, nonpolar compounds that form DNA adducts120 and act as complete carcinogens.123 Coal tar and petroleumproducts such as tar, pitch, coke, carbon black (soot), creosote, anthracene, crude paraffin, asphalt, fuel and diesel oils,lubrication and coolant oils, and untreated mineral oils, as well as oils, waxes, and tars from the distillation products of shaleoil and lignite, contain PAHs.124 High occupational exposures to PAHs can occur in several industries and occupations (seeTable 212-4), and workers can be exposed to PAHs through inhalation or skin contact. The risk for melanoma, as well asinternal cancers, has been reported to be increased in oil refinery workers.125An association between scrotal cancers and the use of cutting oils has been noted, probably related to the addition of shaleoil.126 Used engine oil has also been associated with a case of extramammary Paget disease of the scrotum and groin in apatient with longstanding occupational exposure.127 Creosote used in wood treatment has been suggested as a cause of skin andlip cancer when associated with sunlight exposure.128 Roofers and road pavers are also at increased risk for skin cancers andinternal cancers due to the potential carcinogenicity of bitumen and of PAHs from coal tar products.129 Tar refinery workersare at increased risk of developing nonmelanoma skin cancers, mainly on facial areas, forearms, and hands.130 Use of topicaltar products to treat dermatologic disease has been suggested to pose a skin cancer risk but has never been documented to doso.Fitzpatricks 3745

ANTI-INFLAMMATORY AGENTS

Anti-inflammatory agents in atopic dermatitis, 175176COAL TAR

Coal tar has been used to treat inflammatory dermatoses for up to 2 millennia, although currently it is used primarily to treatpsoriasis.10 Coal tar has been shown to inhibit DNA synthesis and mitosis in epidermal cells, an effect potentiated byultraviolet A exposure.11 Coal tar also has anti-infective, antipruritic, photosensitizing, and vasoconstrictive effects and, withrepeated applications, causes epidermal atrophy. The precise mechanism by which it treats inflammatory skin diseases has notbeen fully described.In 1925, Goekerman pioneered the concomitant use of coal tar and ultraviolet B therapy for psoriasis.Coal tar has historically been messy to use, has an unpleasant odor, and can stain clothing, making its use challenging forsome. Newer formulations, however, might be better tolerated.12,13 Systemic adverse effects are uncommon, whereas localadverse effects can include tar folliculitis, acneiform eruptions, irritant dermatitis, burning, and stinging, allergic contactdermatitis, atrophy, telangiectases, pigmentation, exfoliative dermatitis, and keratoacanthomas.10 Although occupationalexposure to coal tar has been associated with increased risk of developing skin cancer, epidemiologicfitzpatricks 3832