Erythema Multiforme: Recognizing the True Target

Erythema multiforme (EM) is an acute, self-limited hypersensitivity reaction characterized by fixed target lesions of the skin and sometimes the mucous membranes. Herpes simplex virus is the most common trigger, although other infections and medications may also be associated with EM.

But not every annular or target-like eruption represents EM. Recognizing the morphology and distribution of a true target lesion can help distinguish EM from common look-alikes, including erythema migrans and fixed drug eruption.

• To learn more about fixed drug eruptions, our recent blog dives further into the topic.

Look at the distribution

EM typically begins symmetrically on acral sites, particularly the hands and feet, and may spread centripetally. Rather than focusing on a single lesion, look at the eruption as a whole: Are there multiple similar target lesions? Are they concentrated on the extremities?

Don’t forget the mucosa

Mucosal involvement can occur in EM, but it may be absent or limited.

Common look-alikes

Each of these may have target-like lesions (lesions with only 2 zones of color):

• Erythema migrans (of early Lyme disease): The classic presenting sign of erythema migrans is a lesion with a bull’s-eye appearance, which has a pink, red or violaceous rim and a central zone of normal skin. Sometimes the central portion is dusky violaceous or light brown and surrounded by an erythematous or violaceous ring.

• Fixed drug eruption: One or more discrete, round or oval, erythematous or dusky lesions that recur at the same site after exposure to the causative medication. Early on, the lesions may have a pink or red rim, giving them a target-like appearance. Mucosal involvement may occur including lips and genital skin (lesions are also round or oval in these locations).

Key points

• When you see a target-like lesion, don’t stop at the shape.
• Count the zones, consider the distribution and whether the mucous membranes are involved, and look at the eruption as a whole.
• Multiple 3-zone target lesions on the extremities strongly point toward EM.

Resources

VisualDx