The symptoms of erythema nodosum include red lumps that eventually turn purple then brown, high body temperature, joint pain, leg inflammation, and skin swelling and irritation, according to MedlinePlus. The most common site of skin symptoms is on the shins.
Erythema nodosum is a skin disorder that causes reddish nodules under the skin, notes MedlinePlus. Women are at a higher risk of developing erythema nodosum than men. Although the condition may occur without a clear cause, infectious conditions such as hepatitis B, cat scratch disease, streptococcus, tuberculosis and leptospirosis are common causes. Other infections that may cause the condition include chlamydia, histoplasmosis, mycoplasma, mononucleosis and coccidioidomycosis. Reaction to medications such as sulfones, sulfonamides, antibiotics and birth control pills, and disorders such as rheumatic fever, ulcerative colitis, leukemia and Bechet's disease may also result in erythema nodosum.
To diagnose erythema nodosum, a doctor performs a physical exam and other tests, such as a throat culture, chest x-ray or punch biopsy, to determine the underlying cause of the condition, explains MedlinePlus. Depending on the cause, the doctor may recommend nonsteroidal anti-inflammatory drugs, steroids and hot compresses. Resting and use of potassium iodide solution can also treat erythema nodosum. Symptoms often diminish within six weeks.