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 lesions begin as flat, firm, hot, red, painful lumps approximately an inch across. Within a few days they may become purplish, then over several weeks fade to a brownish, flat patch.

Other symptoms may include:

• Fever
• General ill feeling (malaise)
• Joint aches
• Skin redness, inflammation, or irritation
• Swelling of the leg or other affected area

The red and inflamed skin symptoms may regress to a bruise-like appearance.

The diagnosis is primarily based on the appearance of the skin nodules.

Punch biopsy of a nodule may show characteristic changes (septal panniculitis).

Throat culture may be done to reule out a strep infection.

Chest x-ray may be done to rule out sarcoidosis or tuberculosis.