Erythema multiforme is an acute, self-limiting inflammatory skin disease, often accompanied by mucosal membrane damage, with polymorphous skin eruptions. The typical lesions are target-shaped or iris-like. It can be caused by various factors, including infections with bacteria, viruses (especially herpes simplex virus), fungi, or protozoa, as well as certain medications such as sulfonamides, barbiturates, salicylates, and biological products. Some cases are also associated with cold exposure.

bubble_chart Clinical Manifestations

1. The rash is polymorphic, presenting with lesions such as papules, vesicles, bullae, and purpura. The skin lesions are symmetrically distributed, commonly affecting the face, auricles, and distal extremities, and may become generalized in severe cases. 2. Clinically, it is classified into three types based on the characteristics of the skin lesions: **Macular and papular-macular type:** (1) The lesions are round, edematous erythema or flat red papules, slightly depressed in the center, dark red, and may present with vesicles or purplish macules, resembling an iris or target shape. (2) Symmetrically distributed on the dorsum of the hands and feet, forearms, and ankles. (3) Symptoms include cutaneous pruritus or a burning sensation. (4) The course typically lasts 2–4 weeks. **Vesiculobullous type:** (1) Large blisters occur on erythematous bases, which may rupture to form erosions and ulcers. (2) Often accompanied by mucosal lesions in the mouth, eyes, and genital areas. (3) Systemic symptoms include headache, low-grade fever, sore throat, joint and muscle pain, loss of appetite, proteinuria, hematuria, and increased erythrocyte sedimentation rate. **Severe type (also known as Stevens-Johnson syndrome):** (1) Sudden onset with severe systemic symptoms. (2) Skin lesions include edematous erythema, vesicles, bullae, hemorrhagic blisters, and ecchymoses, generalized over the body. (3) Mucosal lesions are severe and extensive. (4) Pain is a prominent symptom. (5) May be accompanied by damage to various internal organs.

1. Polymorphic rash, with symmetrical occurrence of papules, vesicles, bullae, purpura, and other lesions on the face, auricle, and distal extremities; 2. Typical iris-like or target-shaped skin lesions; or generalized bullae, blood blisters, and erosions; 3. Mucosal lesions, such as erosions at mucosal orifices; 4. Systemic symptoms: headache, low-grade fever, joint and muscle pain, loss of appetite, etc.; 5. Subjective cutaneous pruritus, burning sensation, or pain.

bubble_chart Treatment Measures

Principles of Treatment
1. Anti-allergy and antipruritic treatment; 2. Vitamin therapy; 3. For severe cases, treat as severe polymorphic erythema-type drug rash; 4. Topical medication: For mild skin lesions, use mild antipruritic and anti-allergic drugs. For severe cases such as toxic epidermal necrolysis-type drug rash, manage accordingly; 5. Chinese medicine treatment.

Principles of Medication
1. Before treatment, identify and eliminate the disease cause, such as removing the source of infection and discontinuing all suspected allergenic drugs. 2. For mild cases, generally administer oral antihistamines and vitamins, and apply calamine lotion or corticosteroid medicinal paste topically. 3. For patients with bullous or large blister types, administer intravenous calcium, high-dose vitamin C, sodium thiosulfate, etc., along with oral low to moderate doses of corticosteroids and antibiotics as needed. Use wet dressings topically or perform sterile aspiration of blisters. 4. For severe cases, administer high-dose corticosteroids early, enhance wound, oral, and ocular hygiene care, and use potent intravenous antibiotics for infection control. Provide a high-protein diet and supportive therapy, including fluid, electrolyte, and vitamin supplementation, with blood or human albumin transfusion if necessary. 5. For patients with poor response to corticosteroid therapy, consider methylprednisolone pulse therapy.

1. Cure: Symptoms and signs disappear; 2. Improvement: Symptoms and signs improve, skin lesions decrease; 3. No recovery: Symptoms and signs show no improvement.