Erythema nodosum is a condition that causes red nodules (rounded lumps) to form just below the skin surface, most commonly on the shins. In most people, no specific cause or trigger can be found. But in some people a trigger (commonly a streptococcal infection or sarcoidosis) can be identified. Usually, the nodules heal within six to eight weeks with no treatment needed. However, it is important to look for a possible underlying trigger as this may need treatment.
Erythema nodosum is a type of panniculitis. Panniculitis is when there is inflammation of the layer of fat lying underneath the skin. The inflammation causes red nodules (rounded lumps) to form just below the skin surface, which are tender. Erythema nodosum most commonly affects both shins.
In over half of people who develop erythema nodosum, no cause for the inflammation is found. Doctors call this idiopathic erythema nodosum (as idiopathic means of unknown cause).
However, in some people there may be something that triggers (or leads to) the inflammation. In such cases it is thought that erythema nodosum is caused by the immune system becoming hypersensitive (or over-reacting) to the trigger. Such triggers include various infections and other conditions. So, sometimes erythema nodosum may be the first sign of a serious underlying condition that needs to be identified and treated.
Some of the more common triggers for erythema nodosum include:
Erythema nodosum is rare. It affects between 2 and 3 in every 10,000 people per year in the UK. It is most common between the ages of 20 and 35 but it can occur at any age. In adults, erythema nodosum is four times more likely to affect women than men. In children, it affects boys and girls equally.
Before the nodules appear, you may feel generally unwell for a few weeks. You may have a fever, a cough and may lose weight during this time. You may also have aching joints, stiffness and general aches and pains. Your joints may become swollen. Ankle, knee and wrist joints are most commonly affected but any joint can be painful. Aching legs and joints can last for a number of weeks, or even months, after the nodules have appeared.
The nodules (rounded lumps) that occur in erythema nodosum can measure between 2 to 6 cm across. The margins (outlines) of the nodules are not very well defined. The shins are the most common site. Other common sites are on the arms, thighs and trunk but nodules can occur anywhere on the body.
Each nodule tends to last for about two weeks but new nodules can continue to appear for up to six weeks. When the nodule first appears it is usually red, hot and firm to the touch. It then becomes more fluctuant (squashy). As the nodule begins to fade, it looks more like a bruise, turning blue and then yellowish. It usually takes some weeks for the nodules to heal completely. They do not leave any scarring.
You may have as few as two nodules, or as many as 50 or more.
These depend on the trigger. For example, the nodules of erythema nodosum can appear two to three weeks after a streptococcal throat infection. People with inflammatory bowel disease may have abdominal pain and diarrhoea. People with TB may have a cough and breathing problems. Etc.
Your doctor will usually diagnose erythema nodosum by its typical appearance. However, if they are unsure, your doctor may suggest that they refer you to a specialist for a biopsy. During a biopsy, a small sample of tissue is taken from one of the nodules. The tissue sample is then sent to the laboratory to be examined under a microscope. Erythema nodosum has a typical appearance under a microscope and the diagnosis can usually be confirmed.
If your doctor diagnoses erythema nodosum, they will usually suggest some tests to look for an underlying trigger. The tests that they suggest may depend on any other symptoms that you may have. They may include:
The nodules of erythema nodosum tend to go away by themselves and often do not need any treatment. However, they may be very tender or painful and certain treatments may be suggested to help relieve these symptoms.
So, treatments may include:
If an underlying trigger for erythema nodosum has been found, this may need to be treated. The treatment depends on the trigger.
For most people with erythema nodosum the nodules tend to heal, with no scarring, within six to eight weeks. However, in some people with idiopathic erythema nodosum, nodules may last for up to six months or more. Generally, the outlook for erythema nodosum is very good and most people do not have further problems. Chronic (persistent) or recurrent erythema nodosum can occur in some people but this is rare.
As mentioned above, erythema nodosum may be the first sign of an underlying condition such as inflammatory bowel disease or sarcoidosis that needs specific treatment. Each of these conditions has a different prognosis.
An online support group to create the space where people who have been diagnosed with erythema nodosum can share information regarding their experiences in their quest for treatments and cures.