Erythema nodosum

• Erythema nodosum:

  • Type of panniculitis - inflammatory disorder affecting subcutaneous fat
  • Presents as tender red nodules on the anterior shins
  • Less commonly affects the thighs and forearms
• Clinical features:

  • Presents with tender bilateral erythematous subcutaneous nodules 3-20cm in diameter
  • Ill-defined, warm, oval, round or arciform - without ulceration
  • Erupt over 1 to several weeks
  • Resolve within 8 weeks
  • Accompanied by fever and joint pain
  • In half of patients the ankle is swollen and painful for up to several weeks
  • The knees and other joints can also be affected
  • Does not cause permanent scarring
• It is caused by a hypersensitivity reaction. In around half of patients there is no identifiable cause. It is associated with a number of triggers and underlying conditions.
• Causes of hypersensitivity reaction:

  • Streptococcal throat infection
  • Gastroenteritis
  • Mycoplasma pneumoniae
  • TB
  • Pregnancy
  • Medications - NSAIDs, oral contraceptive, antibiotics
• Associated chronic diseases (inflammatory):

  • IBD
  • Sarcoidosis
  • Lymphoma
  • Leukaemia
  • Behcet disease
• The diagnosis of erythema nodosum is based on the clinical presentation. Investigations can be helpful in assessing the underlying cause:

  • Inflammatory markers (CRP and ESR)
  • Throat swab for streptococcal infection
  • Chest xray can help identify mycoplasma, tuberculosis, sarcoidosis and lymphoma
  • Stool microscopy and culture for campylobacter and salmonella
  • Faecal calprotectin for inflammatory bowel disease
• Management mainly involves investigating for an underlying condition and treating the underlying cause.

  Erythema nodosum is managed conservatively with rest and analgesia. Steroids may be used to help settle the inflammation.

  Most cases will fully resolve within 6 weeks, however it can last longer.