Erythema nodosum is a type of skin inflammation that is located in a certain portion of the fatty layer of skin. Erythema nodosum (also called EN) results in reddish, painful, tender lumps most commonly located in the front of the legs below the knees. The tender lumps, or nodules, of erythema nodosum range in size from one to five centimeters. The nodular swelling is caused by a special pattern of inflammation in the fatty layer of skin.
In half of the people who develop erythema nodosum, no cause for the inflammation is found. However, in some people there may be something that triggers the inflammation. In such cases it is thought that EN is caused by the immune system becoming hypersensitive (or over-reacting) to the trigger. Such triggers include various infections and other conditions. Also, erythema nodosum may be the first sign of a serious underlying condition that needs to be identified and treated.
Erythema nodosum can be self-limited and resolve on its own in three to six weeks. Upon resolution, it may leave only a temporary bruised appearance or leave a chronic indentation in the skin where the fatty layer has been injured.
Treatments for erythema nodosum include anti-inflammatory drugs such as cortisone. Colchicine is sometimes used effectively to reduce inflammation and prevent recurrence. Treatment must be customized for the particular patient and conditions present, such as the existence of any associated diseases. It is important to note that erythema nodosum, while annoying and often painful, does not threaten internal organs and the long-term outlook is generally very good.