Erythema multiforme (EM) is an immune-mediated skin reaction characterized by a distinctive rash that appears in response to a trigger, most often an infection. The rash itself is not contagious and cannot be spread from person to person through contact or shared objects. EM represents an individual hypersensitivity response—the body’s overreaction to an internal issue—and is not a transmissible infection.
Defining Erythema Multiforme
Erythema multiforme is a mucocutaneous inflammatory condition that is typically self-limiting, meaning it resolves on its own. The defining physical sign of EM is the appearance of “target lesions” or “iris lesions” on the skin. These lesions are round and classically feature three concentric rings of color variation, resembling a bull’s-eye.
The lesions often appear symmetrically on the extremities, such as the hands, feet, arms, and legs, and can be itchy or painful. The condition is broadly classified into two types based on severity and extent of involvement.
Erythema Multiforme Minor
Erythema Multiforme Minor is the milder, more common form. It usually affects only the skin with minimal to no involvement of the mucous membranes.
Erythema Multiforme Major
Erythema Multiforme Major is the more severe presentation. It involves extensive skin lesions and significant blistering or erosions on at least two different mucosal surfaces, such as the mouth, eyes, or genitals. The oral mucosa is the most frequently affected site in major cases, which can make eating and drinking difficult. Systemic symptoms like fever are also common in the major form.
Addressing Contagion and Transmission
The skin lesions of erythema multiforme are the result of an immune system response that mistakenly targets skin cells. They do not contain a transmissible agent. Therefore, the EM rash cannot be transmitted to another person through direct contact or airborne droplets.
EM is a hypersensitivity reaction, not a primary infectious disease. While the underlying trigger, such as a virus, may be contagious, the resulting skin reaction is a unique and non-transmissible event within the affected individual. There is no need to isolate a person with EM to prevent the spread of the rash.
Common Triggers and Underlying Causes
Erythema multiforme is an immune-mediated reaction where the body’s defense system is activated by an external agent and then launches an attack against its own skin cells. Infections are the most frequent cause, accounting for approximately 90% of cases. The resulting rash is a type IV hypersensitivity reaction, where specific T-cells in the immune system target skin keratinocytes.
Infectious Triggers
The most common trigger is the Herpes Simplex Virus (HSV), specifically type 1 and type 2. The EM rash typically appears about 10 days after a herpes flare-up. The immune system detects viral DNA fragments from the reactivated HSV within the skin cells, which triggers the widespread inflammatory response.
Another significant infectious trigger, particularly in children, is the bacterium Mycoplasma pneumoniae. This bacterium causes a form of atypical pneumonia. In these cases, the respiratory symptoms may precede the onset of the skin rash. Other infections, including Epstein-Barr virus, influenza, and various fungal infections, have also been associated with EM.
Medication Triggers
Medications are a less common, but recognized, trigger for erythema multiforme, accounting for under 10% of cases. Common drug culprits include certain antibiotics, such as penicillins and sulfonamides, as well as nonsteroidal anti-inflammatory drugs (NSAIDs) and anti-epileptic medications. In drug-induced cases, the body’s immune system may react to metabolites of the medication, leading to the cutaneous reaction.
Managing the Condition
Management of erythema multiforme focuses on alleviating symptoms and addressing the underlying trigger when it is identified. The condition is often self-limiting, with lesions typically resolving within two to four weeks without leaving scars. Supportive care is the primary approach for mild cases.
For skin symptoms, topical steroids and oral antihistamines can be used to help reduce itching and inflammation. If the mouth is involved, topical anesthetics and antiseptic mouthwashes can provide relief for painful oral lesions. This helps ensure the patient can maintain adequate hydration and nutrition.
In cases where HSV is confirmed as the trigger, antiviral medications like acyclovir or valacyclovir may be prescribed to treat the underlying virus and prevent future recurrences. For patients with recurrent EM linked to HSV, continuous prophylactic antiviral therapy may be recommended to suppress the virus and reduce the frequency of future EM episodes.
Urgent medical attention is necessary if a patient exhibits signs of more severe disease, such as extensive blistering, a high fever, or significant difficulty swallowing. Severe cases of EM Major may require hospitalization for pain management, intravenous fluids to prevent dehydration, and specialized supportive care.