Erythema multiforme (EM) is an acute, self-limited skin condition resulting from a hypersensitivity reaction, usually triggered by an infection or medication. This reaction causes a distinctive rash on the skin and sometimes the mucous membranes. Erythema multiforme is not contagious; it cannot be spread from person to person through casual contact or airborne transmission. The condition is an immune response within the body, not a transmissible infection.
The Defining Characteristics of Erythema Multiforme
Erythema multiforme is characterized by a symmetrically distributed rash that often appears suddenly on the extremities, such as the hands and feet, before potentially spreading to the torso. The hallmark sign is the “target” or “iris” lesion, which looks like a bull’s-eye. This lesion typically has three distinct zones: a dark or dusky center, a pale ring of swelling, and an outer ring of redness.
The condition is categorized into Erythema Multiforme Minor and Erythema Multiforme Major. EM Minor is the more common and milder presentation, involving skin lesions with minimal or no involvement of the mucous membranes. EM Major is the more severe form, featuring a more extensive skin rash and significant involvement of at least two mucosal sites, such as the mouth, eyes, or genitals. These mucosal lesions often develop into painful blisters and erosions that can make eating or swallowing difficult.
Primary Triggers and Underlying Causes
The appearance of erythema multiforme is a delayed type IV hypersensitivity reaction, where the immune system mistakenly targets cells in the skin and mucous membranes. This immune overreaction is almost always set off by an external trigger, grouped into infections or medications. The most frequent trigger for EM, especially the minor form, is an infection with the Herpes Simplex Virus (HSV), which causes cold sores and genital herpes.
The rash typically develops about a week or two after an HSV outbreak, even a mild one. Another common infectious cause is the bacterium Mycoplasma pneumoniae, a known cause of respiratory infections. While the infection itself may be contagious, the subsequent immune reaction of EM is not transmissible to another person.
Medications are the second major category of triggers, and they are more commonly associated with the more severe EM Major form. These reactions can be caused by certain antibiotics, such as sulfonamides and penicillin, as well as some nonsteroidal anti-inflammatory drugs (NSAIDs) and anticonvulsants. If a medication is identified as the cause, discontinuing the drug is a necessary step in management.
Treatment and Management
Treatment for erythema multiforme is primarily supportive, focusing on managing symptoms while the condition runs its course, as most cases are self-limiting and typically resolve within two to four weeks. For mild cases, over-the-counter pain relievers and oral antihistamines can help manage discomfort and itching. Topical corticosteroids may also be applied to the skin lesions to reduce inflammation.
Supportive care is particularly important for EM Major, which may require hospitalization to manage severe mucosal involvement and prevent dehydration. Oral lesions can be treated with topical anesthetics and antiseptic mouthwashes to allow for easier eating and drinking.
For individuals who experience recurrent episodes of EM linked to the Herpes Simplex Virus, a doctor may recommend prophylactic antiviral medication. Long-term use of drugs like acyclovir or valacyclovir can suppress the underlying viral trigger and prevent future outbreaks. People with any sign of eye involvement or difficulty swallowing should seek immediate medical attention to ensure proper care.