EM is an acute, widely distributed hypersensitivity reaction associated with circulating immune complexes that are deposited in the basement membranes of the superficial vessels of the skin and mucosa. Subsequent complement activation produces vasculitis and thrombosis, leading to tissue ischemia and necrosis of the adjacent epithelium. The intensity of the skin and mucosal reaction varies from a localized minimal erythematous
response to frank epithelial necrosis. Commonly identified precipitating factors include infections (herpes simplex, Mycoplasma pneumoniae) and medications (sulfonamides, barbiturates, and penicillin)—"drugs and bugs." Based on the intensity and severity of the hypersensitivity response, EM is classified into minor and major forms, with StevensJohnson syndrome (Chapter 22) and toxic epidermal necrolysis representing progressively more severe involvement, morbidity, and associated mortality. A multiday prodrome of fever, malaise, and headache precedes development of the mucocutaneous lesions. The classic skin lesion of EM is a concentric erythematous lesion described as resembling a target or bulls-eye. Oral mucosal lesions vary from focal aphthous-like involvement to diffuse areas of erythema, bulla formation, and ulceration (Fig. 6). Bullae collapse rapidly, leaving pseudomembrane-covered surfaces. The lips often appear hemorrhagic and crusted (Fig. 40).
EM is often described as a diagnosis of exclusion. Biopsy with DIF examination may be useful in excluding other disease processes with a similar clinical appearance, as well as in providing additional supportive findings. DIF reveals a perivascular deposition of immunoreactants (IgM and C3) around superficial blood vessels. Association of the lesions with a medication or an infection is supportive. An exfoliative cytologic spear can help rule out primary herpes.
FIGURE 41 Contact stomatitis to nickel in orthodontic wire. This individual tolerated the placement of metal brackets on the teeth for an extended period. Shortly after inserting a nickel-containing orthodontic wire into the brackets, these painful erythematous patches arose on the buccal mucosa. The lesions cleared after removal of the wire. The metal brackets remained in place. Source: From Ref. 38.
FIGURE 42 Contact allergy to cinnamon flavoring. This adult male chewed of cinnamon-flavored chewing gum and complained of a long-standing soreness of his buccal mucosa. Note the irregular ulcers, covered by fibrinous membranes, surrounded by white areas. The lesion completely healed within two weeks after withdrawal of the gum. Source: Courtesy of Charles Dunlap, DDS.
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