What is erythema multiforme?
Erythema multiforme (EM) is an acute skin condition that may be recurrent in some cases. It occurs most commonly in association with the herpes simplex virus as an immune response to the infection. Young males are most commonly affected.
There are two types of EM – EM minor and EM major. EM minor is a milder form of the condition with no mucosal involvement. EM major is a more severe, potentially life-threatening condition with one or more mucosal sites involved (e.g. inside eyes, mouth, genitalia). EM minor tends to be limited to the extremities, whilst EM major tends to start on the face and trunk and is more widespread.
What causes erythema multiforme?
Most cases are triggered by the herpes simplex virus, in the form of a cold sore or, less commonly, genital herpes. Other cases are associated with a chest infection such as mycoplasma pneumonia.
EM major is more frequently due to a reaction to medications such as antibiotics, non-steroidal anti-inflammatory drugs and anti-epileptics.
What does erythema multiforme look like?
Mild symptoms including feeling unwell, low-grade fevers, sore joints or coughing may precede the classic rash. Early on, itching and burning in the skin may be present. In some cases there may be no preceding symptoms.
EM starts abruptly over two to three days as dull, red spots, which later become raised or blistered. The condition progresses into classic target-like lesions consisting of concentric rings. Typically there is a dusky/purple pink centre, surrounded by a zone of pale pink and an outer red ring. Commonly, these occur on the palms, soles and extremities. The lesions often come up as clusters in a symmetrical distribution.
EM major typically involves mucosal surfaces with painful blistering, ulceration and crusting. Affected individuals are often quite unwell with high fevers and may have enlarged lymph glands.
How is erythema multiforme diagnosed?
The diagnosis is usually based on the classic target-like appearance and distribution of the rash. A biopsy may be taken to confirm the diagnosis. A swab or blood test may be required to look for an underlying cause.
How is erythema multiforme treated?
Treatment depends on the severity of the condition. If a drug is suspected it must be ceased. Topical steroids may be prescribed to help with itching. If mucosal membranes are affected, hospitalisation may be required for more severe cases. An eye specialist may be involved if the eyes are affected.
Those with recurrent EM are often associated with herpes simplex virus, and prophylactic anti-viral medications can be helpful in such cases.
EM minor is not serious and usually heals without any complications in 3 to 4 weeks. EM major can rarely result in permanent scarring on mucosal sites, such as the eyes.
This information has been written by Dr Yin Vun