What is erythema multiforme?
Erythema multiforme (EM) is a skin condition with red spots and/or blisters on the skin. It usually develops after a (viral) infection or after medicine use. As the name suggests, EM can take many forms; to allow classification, three groups are distinguished. Common are the typical ring-shaped spots, but blisters and hive-like spots also occur.
1) Erythema multiforme minor
By far the most common form, consisting of red to purple spots located mainly on the arms and legs and, in more extensive cases, the trunk. In the most typical cases there are “target” lesions: spots built up of several concentric rings, often (but not always) with blisters. Red spots and blisters are also often seen on the mouth lining. EM minor is usually caused by an infection.
2) Erythema multiforme major
Besides skin changes, the “major” variant also has extensive erosions of the mucous membranes; the mouth, eyes, vagina and anus can be affected. The patient is often ill, has a lot of pain and can eat with difficulty because of the open areas. Admission to hospital is usually warranted. Here too an infection is usually (but not always) the trigger.
3) Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN)
These are the rarest and most severe forms, in which large parts of the skin can detach. SJS and TEN are usually a reaction to a medicine. When less than 10% of the skin surface is affected we speak of SJS, and when more than 30% is involved we call it TEN (between 10 and 30% is an SJS/TEN overlap). With SJS and certainly with TEN the patient is usually seriously ill and must be nursed in an intensive care unit; the greatest threats are dehydration through evaporation and infections. The medicine that caused the reaction must of course never be taken again.
Besides infections and medicines, other underlying causes of erythema multiforme include parasitic infections, cancers and autoimmune diseases such as lupus erythematosus and vasculitis, though these are rarer than infections and medicines.
How is erythema multiforme treated?
The most common cause of EM is a viral infection, and a herpes infection often proves to be the cause. For an (early) herpes infection, treating the infection is useful, and when herpes simplex (for example a cold sore) is the cause and recurs several times a year with EM, a preventive maintenance treatment with antiviral medicines can be considered.
How are SJS and TEN treated?
When medicine use is the most likely cause (as it usually is with SJS and TEN), the suspected medicine must be stopped (in consultation with the prescribing doctor). Good observation is important, because the skin and mucous membrane complaints can spread even after stopping the trigger. In more severe cases, supportive measures such as pain relief, itch relief, inflammation suppression or even hospital admission are necessary.
When to see a doctor
See a doctor promptly for a rash of target-shaped spots or blisters, and urgently if there are painful sores in the mouth, eyes or genitals, widespread blistering, skin peeling or feeling very unwell — this can be a severe drug reaction needing emergency care.