Erythema Multiforme 

Erythema multiforme cannot be caught from someone else, but is a reaction that can be triggered by a variety of things, the most common of which are viral infections (90%) and medications (10%). 

• • In children, and in mild erythema multiforme, an infection a few days before the rash starts is the usual trigger. This is most commonly due to herpes simplex (the cold sore virus), which should be suspected if the erythema multiforme flares up repeatedly. A chest infection by germs called mycoplasmas is also a common cause. 
    
  • Reactions to medications cause most of the severe cases of erythema multiforme. The drugs that do this most often are those used to treat infections - such as sulfonamides, tetracyclines, amoxicillin, and ampicillin. Next come non-steroidal anti-inflammatory drugs (given for arthritis) and anticonvulsants (used to treat epilepsy). Many other drugs can occasionally trigger erythema multiforme.
    
  • The most common single cause of erythema multiforme is the herpes simplex (cold sore) virus, but in about half of all cases no one can find the trigger.
    
  • Erythema multiforme occurs most commonly between the ages of 10 and 40.
    
  • Erythema multiforme is not hereditary.

This depends on how bad it is. If you have it mildly, you may feel perfectly well, and your rash may just be slightly uncomfortable. 

If your erythema multiforme is more severe, you may have a fever and a headache, and feel unwell for a few days before the rash appears. Blisters on your skin may break down and leave painful raw areas. If your eyes are affected, you may become sensitive to light and notice blurring of your vision. Raw areas inside the mouth can make it hard to eat and drink, and genital soreness can interfere with passing water. Even when the rash has cleared up, a few people are left with scars on their skin, or with damaged eyes.

No one can guarantee that erythema multiforme will not come back, particularly if it follows recurrent cold sores. However, most patients with erythema multiforme recover completely.

In mild Erythema Multiforme

• The spots usually come up over the course of 3 or 4 days, starting on the hands and feet, and then spreading up the limbs to the trunk and face.
  
• At first the spots are small, round, slightly raised red areas, some of which turn into the ‘target lesions’ described above.
• These are 1-3 cm across, but may fuse together to produce larger areas. Small blisters form in the centre of some of the targets.
  
• The rash usually fades over 2 to 4 weeks, but recurrences are common.

In severe Erythema Multiforme

• You may feel ill and have a high temperature.
  
• The spots are usually larger, and run into each other more than those of mild erythema multiforme, but ‘target lesions’ can usually still be seen.
  
• Large blisters may form, and then burst to leave red oozing areas.
  
• Your lips may be covered with crusts, large raw areas may appear inside your mouth, and your eyes may swell up and turn red.

Diagnosing Erythema Multiforme 

There are no specific blood tests for erythema multiforme. The diagnosis is usually based on the way the rash looks, the way it is distributed symmetrically over the skin, and exposure to one of the known triggers discussed above. Occasionally it is necessary to remove a small sample of skin under a local anesthetic to confirm the diagnosis under the microscope. 

Your doctor will try to find out what caused the erythema multiforme in the first place. If a particular drug is suspected, it must be stopped straight away.

Will depend on how bad the erythema multiforme is

• Mild attacks will clear up in a few weeks with simple lotions or corticosteroid applications.
  
• Severe attacks can be life threatening. Patients may need to be nursed in hospital, perhaps in a burns unit, using dressings like those needed for an extensive burn. The pain from the raw areas can be severe and must be controlled. The oozing areas can leak large amounts of fluid and this will be monitored and replaced. A liquid diet may be needed.  Antibiotics help if the damaged skin is infected. Short courses of corticosteroid tablets are sometimes given to try to make the rash go away more quickly. An eye specialist should be asked to advise on any problems with the eyes.
  
• Recurrent attacks may be a problem. If they always follow a cold sore, and come up several times a year, it may be worth taking a small daily dose of a drug designed to suppress the herpes simplex virus for several months

What you can do

• If you have had one attack of erythema multiforme, remember there is a risk that you will have another one.
  
• Avoid all medications that were suspected of causing your earlier attack.
  
• If your attacks follow cold sores, you may want to ask your doctor about taking antiviral tablets long-term.