Erythema nodosum

Erythema nodosum (EN) is an inflammation of subcutaneous fat caused by a delayed hypersensitivity reaction. Women in early adulthood are commonly affected. Most cases are idiopathic, but an association with a variety of diseases, including infections and autoimmune disorders (e.g., ulcerative colitis), is possible. The characteristic lesions are painful nodules on the lower legs (particularly shins). EN is a clinical diagnosis. The condition typically heals spontaneously within a few weeks and, therefore, generally requires no more treatment than supportive care (e.g., analgesia).

• Sex: ♀ > ♂
• Peak incidence: 18–34 years

References:^[1]

Epidemiological data refers to the US, unless otherwise specified.

• Idiopathic (most common)
• Infection (e.g. streptococcal pharyngitis, histoplasmosis, coccidioidomycosis, TB, leprosy)
• Autoimmune diseases (e.g. sarcoidosis, Crohn disease, ulcerative colitis, Behcet syndrome)
• Drugs (oral contraceptives, sulfonamides, iodide)
• Pregnancy
• Malignancy

References:^[2][3]

• Delayed hypersensitivity reaction → panniculitis (inflammation of subcutaneous fat)

References:^[2][3]

• Nonspecific symptoms: : fever, arthralgia
• Painful, subcutaneous nodules on both pretibial (anterior leg) surfaces (less common on other areas of skin)
  1. Firm, erythematous (1^st week)
  2. Fluctuant (without suppuration) and bluish (2^nd week)
  3. Progressively fades (i.e., yellow or brown hue)

References:^[2][3]

• Clinical diagnosis
• Imaging and laboratory tests determine the underlying condition
  • CBC, ESR
  • Antistreptolysin-O titer; throat or blood culture
  • Chest x-ray: hilar lymphadenopathy (e.g., in sarcoidosis, tuberculosis)
  • VDRL
  • Inflammatory bowel disease workup
• Skin biopsy if diagnosis is uncertain

References:^[2]

• Symptomatic treatment
  • Bed rest
  • Leg elevation
  • Heat or cool compresses
  • NSAIDS (e.g., ibuprofen)
  • Potassium iodide
• Treat underlying disease
• In severe or refractory cases: systemic steroids

References:^[2]

• Usually self-limiting (within 2–8 weeks), or resolves earlier with effective treatment of underlying disease
• Recurrence following discontinued treatment is common

References:^[2][4]