Definition of Erythema nodosum:

Erythema nodosum is an inflammatory disorder that is characterized by tender, red nodules under the skin.

Causes, incidence, and risk factors:

The exact cause of erythema nodosum is unknown. Some cases may be associated with the following:

• Infections:
  • Streptococcus
  • Coccidioidomycosis
  • Tuberculosis
  • Hepatitis B
  • Syphilis
  • Cat scratch disease
  • Tularemia
  • Yersinia
  • Leptospirosis
  • Psittacosis
  • Histoplasmosis
  • Mononucleosis (EBV)
• Sensitivity to certain medications:
  • Oral contraceptives
  • Penicillin
  • Sulfonamides
  • Sulfones
  • Barbiturates
  • Hydantoin
  • Phenacetin
  • Salicylates
  • Iodides
  • Progestin

Other associated disorders include leukemia, sarcoidosis, rheumatic fever, and ulcerative colitis.

Erythema nodosum is most common on the shins, but it may also occur on other areas of the body (buttocks, calves, ankles, thighs and upper extremities). 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. Systemic (whole body) findings may include fever and malaise.

The condition is more common in women than men.