Erythema nodosum (also called EN) is a type of skin inflammation disorder that is characterized by tender red nodules under the skin. EN is usually located in a certain portion of the fatty layer of skin. EN results in reddish, painful, tender lumps most commonly located in the front of the legs below the knees.
Erythema nodosum is most common on the shins but it may also occur on other areas of the body (buttocks, calves, ankles, thighs, and arms). The tender lumps or nodules of erythema nodosum range in size. The nodular swelling is caused by a special pattern of inflammation in the fatty layer of skin. The lesions begin as flat, firm, hot, red, painful lumps approximately an inch across. Within a few days they may become purplish and over several weeks fade to a brownish, flat patch.
EN is more common in women than it is in men. Erythema nodosum is uncomfortable but it is usually not dangerous. 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.
There are several scenarios for the outcome of erythema nodosum. Typically, these areas of nodular tenderness range in size from about a dime to a quarter and they may be tender and inflamed off and on for a period of weeks. They usually then resolve spontaneously, each one of the little areas of inflammation shrinking down and then becoming flat rather than raised and inflamed. They leave a bruised appearance. Then, they resolve spontaneously completely. Other lesions can sometimes pop up elsewhere. This may occur for periods of weeks to months and then eventually goes away. However, chronic erythema nodosum that may last for years is another pattern. Chronic erythema nodosum with intermittent recurrences can occur with or without an underlying disease present.
Other symptoms of EN may include fever, general ill feeling (malaise), joint aches, skin redness, inflammation or irritation and swelling of the leg or other affected area.
In about half of the cases, the exact cause of erythema nodosum is unknown.