Erythema multiforme. Although most cases of erythema multiforme do not have bullae or crusts, some do. Erythema multiforme major is usually characterized by fewer but larger lesions that tend to have bullae or crusts. Antibiotics are sometimes given when a skin infection is erroneously thought to be the cause.
Erythema multiforme is often initially misdiagnosed because it may appear similar to or mimic more common conditions. When the cause is a drug and the patient is diagnosed with a drug rash, there is usually no harm done and the patient improves. Fortunately, most other cases are benign and resolve on their own with time, but some can progress to more severe conditions or be caused by diseases that may require treatment, such as hepatitis B or cancers. For this reason, it is useful to be on the lookout for this disease.
Most cases present with target and serpiginous lesions that, unlike many other skin conditions, may involve the palms. While most allergic skin reactions tend to be pruritic more than painful and most infectious skin conditions tend to be mostly painful, erythema multiforme tends to be equally itchy and painful. Occasionally, there are fewer but larger lesions as in this case. These larger lesions often form small superficial bullae that eventually rupture and become crusts that look a lot impetigo, but they are unusually circular and tend to be in areas where impetigo is less common.
Treatment of erythema multiforme is primarily symptomatic with antihistamines, especially H2 blockers, for itching, cool compresses for itching or pain, and acetaminophen for pain. More importantly, one should try to determine the cause. For most causes there is no definitive treatment, however. If any mucous membranes are involved or if there are large areas of desquamation, one should consider the more severe variants of erythema multiforme, namely Stevens-Johnson syndrome and toxic epidermal necrolysis, which usually require admission.
Brady Pregerson, MD, is an emergency physician at Cedars-Sinai Medical Center in Los Angeles and at Tri-City Medical Center in Oceanside, California.
Pregerson B. Emergency Medicine1-Minute Consult Pocketbook. 5th ed. EMresource.org; 2017.