Erythema Multiforme

What is erythema multiforme?

Erythema multiforme (EM) is a skin hypersensitivity reaction primarily triggered by certain infections, notably Herpes Simplex Virus (HSV, often known as the cold sore virus) and Mycoplasma pneumoniae. It presents as distinct target-like lesions, different from those seen in Stevens-Johnson syndrome (SJS). Some cases also show mucous membrane involvement. Although erythema multiforme is generally self-limiting and resolves without complications, it is important not to confuse it with SJS. Previously, the two were grouped together, but that is no longer the case. SJS is a severe condition that can be life-threatening, often resulting from drug reactions.

What causes erythema multiforme?

The primary trigger for erythema multiforme is an infection. The most frequent culprits are Herpes Simplex Virus (cold sore virus) infections and mycoplasma (walking pneumonia). Typically, the rash appears 3-14 days following the infection. Other triggers for erythema multiforme include:

• Varicella-zoster virus (responsible for chickenpox and shingles)

• Adenovirus

• Hepatitis viruses

• Human immunodeficiency virus (HIV)

• Cytomegalovirus

• Parapoxvirus

What are the symptoms of erythema multiforme?

Erythema multiforme manifests as target lesions, ranging from a few to hundreds, that appear over a day. These lesions are defined by a central red or dark spot that may blister or crust, encircled by a pale ring, and an outermost bright red ring. The lesions often commence on the extremities, moving towards the torso, neck, and face. They can expand over three days and may be accompanied by a slight burning or itching sensation. The chronic form of erythema multiforme tends to develop at trauma sites.

The condition is classified as erythema multiforme minor when it's limited to the skin. If the mouth, eyes, or genitals are affected, it's termed erythema multiforme major. Mucosal involvement generally begins with the lips and inner cheek turning red, potentially progressing to blisters or ulcers. Swollen lips and difficulty swallowing can also be symptoms. Other mucous membranes can occasionally be affected.

How do I treat erythema multiforme?

While erythema multiforme might not always require treatment, it's advisable to consult a specialist to rule out more serious conditions. Addressing the root cause, such as treating the initial infection, is usually recommended. This might involve antiviral medications like aciclovir or valaciclovir for HSV or antibiotics for Mycoplasma pneumoniae. Symptomatic treatments can include:

• Topical steroids

• Antihistamines (for itchiness)

• Anesthetic mouthwash (for oral symptoms)

• Hospitalization in cases of significant difficulty in drinking or eye complications