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- Erythema multiforme (EM) is an acute, self-limited hypersensitivity reaction:
- Mostly triggered by infectious agents (up to 50% by herpes simplex virus [HSV]-1 or -2) or drugs (1,2)
- Involving the skin and the mucous membrane, most commonly the mouth (60–70% of all EM patients have oral lesions) (3)
- Skin lesions include raised typical target or “iris” lesions or raised atypical lesions predominantly involving the extremities; flat, atypical lesions and macules with or without blisters are more suggestive of Stevens-Johnson (SJS) or toxic epidermal necrolysis (TEN) (4).
- Currently, there are no universal diagnostic criteria for EM. It was previously considered a spectrum of disease, consisting of EM, EM major, SJS, and TEN; however, a growing consensus believes EM is a condition distinct from SJS and TEN due to the differences in clinical presentation, histopathologic features, patient demographics, possible etiology and pathogenesis, and treatment plan (1,2,4,5,6).
- 2 subtypes, erythema multiforme minor (EMm) and erythema multiforme major (EMM), with the former involving none or 1 mucous membrane, and the latter involving at least 2 mucous membrane sites (1)
- Recurrent EM is defined as >3 attacks, but has a mean number of 6 attacks (range 2–24) per year and a mean duration of 6-9.5 years (range 2–36) (1,7).
Annual US incidence is estimated at 0.01–1% (6).
Previous history of EM
Strong association with HLA-DQ3 in herpes-related cases; possible association in recurrent cases with HLA-B15, -B35, -A33, -DR53, DQB1*0301, and DQW3 (1)
- The exact pathophysiology of EM is unknown.
- Possible immunologically mediated lymphocytic reaction to an infectious agent or a drug at the dermal-epidermal junction
- HSV-triggered EM seems to involve CD4+ T-cell infiltration and associated IFN-γ activation.
- Drug-triggered EM involves CD8+ T-cells and associated TNF-α activation (6).
- Most cases appear to be due to a preceding infection.
- Viral infections, particularly HSV (up to 50% of cases); also Epstein-Barr, coxsackie, echovirus, varicella, mumps, poliovirus, hepatitis C, cytomegalovirus, HIV, molluscum contagiosum virus
- Bacterial infections, particularly Mycoplasma pneumoniae; other reported bacterial infections include Treponema, Pallidum, and Gardnerella vaginalis
- Fungal infection, including Histoplasma capsulatum and Coccidioides immitis
- Medications, including sulfonamides, penicillins, anticonvulsants (carbamazepine, phenytoin, phenylbutazone, phenothiazines, barbiturates), hydantoins, NSAIDs (including rofecoxib, valdecoxib), oral contraceptives, and statins. Other sparsely reported medications include cimetidine, salicylic acid, angiotensin receptor blockers (ARBs; ccandesartancilexetil), metformin, bupropion, ciprofloxacin, sorafenib, gemfibrozil, risperidone, paclitaxel, metoprolol, tumor necrosis factor (TNF) inhibitors (adalimumab, etanercept, infliximab), and methotrexate (3)
- Vaccines: Tetanus/Diphtheria, bacillus Calmette-Guérin, oral polio, hepatitis B, human papillomavirus, H1N1 influenza
- Occupational exposures: Herbicides (alachlor and butachlor), iodoacetonitrile
- Protozoan infections
- Radiation therapy
- Premenstrual hormone changes
Commonly Associated Conditions
See “Etiology” above.