The clinical presentation of EM can range from a mild, self-limited exanthematous form to a progressive, fulminating, life-threatening variant with extensive mucocutaneous epithelial necrosis. The skin lesions are usually macules (or erythematous papules in mild cases) with some target lesions. Such lesions are <3 cm in diameter and demonstrate concentric zones of color change, with the central region revealing a bulla or crust. The lesions have a regular round contour with a well-defined border. Target lesions may have a central dusky zone and one or two outer zones with a reddish hue. Occasionally bullae will develop. In more severe forms of EM, the target lesions are typically more raised and palpable.

Oral involvement is very common, especially in more severe EM major. Lips can be swollen and cracked, and they usually bleed easily in areas of crusting. Intraoral lesions are also seen in more severe cases of EM major, and diffuse, widespread blistering and ulceration can be present.

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There are no specific diagnostic tests for EM. The diagnosis is made clinically and supported by skin biopsy, which can rule out lupus and vasculitis. The histologic signs of EM are somewhat nonspecific. Typically, intraepithelial edema and spongiosis are found early; satellite cell necrosis, vacuolar degeneration of the basement membrane zone, and severe papillary edema with subepidermal vesiculation occur later. Intense infiltration of T lymphocytes and mononuclear cells is seen in the basement membrane and dermal regions. Immunofluorescence also is not diagnostic, with immune deposits of immunoglobulin M, C3 complement, and fibrin normally noted at the basement membrane zone.

The differential diagnosis of severe EM includes urticaria, cutaneous lupus, mycosis fungoides, granuloma annulare, fixed drug eruption, erythema annulare certrifugum, vasculitis, pemphigus, pemphigoid, viral stomatitides, and toxic epidermal necrolysis. Features suggestive of EM include acute onset, with all lesions appearing within the first 72 hours and lasting at least seven days; a recurrent nature; oral erosions on the lip and anterior part of the mouth; and pleomorphic skin lesions with a central zone reflecting damage (dusky, bullous, or crusted).

Treatment of EM begins with immediate withdrawal of any precipitating medication and treatment of any causal infections (such as herpes). In cases of EM minor, spontaneous healing occurs without sequelae over a period of two to three weeks. Patients experience an uncomplicated course; however recurrences are common. Topical steroids and oral histamines for a week is the usual protocol, as is prophylactic use of oral acyclovir for several months in my practice.

With EM major, although no specific treatment is available, supportive care is important. Analgesics, liquid diets, correction of fluid and electrolyte imbalances, skilled nursing care, and monitoring of urinary output may be necessary. Patients may need ophthalmologic care, pulmonary toilet, and protection from secondary infection. Oral corticosteroids have traditionally been the most commonly used drug for EM major. Patients with EM major may require hospital care, as supplemental hydration or alimentation may be needed, depending on the severity of oral cavity involvement. Other systemic treatments may include cyclosporine, dapsone, azathioprine (Imuran), cyclophosphamide, levamisole (Ergamisol), IV immunoglobulin, and thalidomide (Thalomid).

Our patient with EM minor was started on topical steroids and oral antihistamines. She was instructed to inform her other physicians of a possible allergy to sulfa. Additionally, she was prescribed oral acyclovir, which she was to take for a few months and restart if she experienced a recurrence of EM in the future.

Dr. Burkhart is clinical professor of dermatology at the University of Toledo College of Medicine in Ohio and clinical assistant professor of dermatology at Ohio University College of Osteopathic Medicine, in Athens.