- Clinical science
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
Epidemiological data refers to the US, unless otherwise specified.
- Nonspecific symptoms: : fever, arthralgia , malaise, hilar lymphadenopathy
Painful, subcutaneous nodules on both pretibial (anterior leg) surfaces (less common on other areas of skin)
- Firm, erythematous (1st week)
- Fluctuant (without suppuration) and bluish (2nd week)
- Progressively fades (i.e., yellow or brown hue)
- Clinical diagnosis
- Imaging and laboratory tests determine the underlying condition
- Skin biopsy if diagnosis is uncertain
- Usually self-limiting (within 2–8 weeks), or resolves earlier with effective treatment of underlying disease
- Recurrence following discontinued treatment is common