From the Guidelines
Erythema nodosum is characterized by raised, tender, red or violet subcutaneous nodules.
Key Characteristics
- The nodules are typically 1–5 cm in diameter 1
- They commonly affect the extensor surfaces of the extremities, particularly the anterior tibial areas 1
- A firm clinical diagnosis can normally be made based on physical exam, and biopsy is not usually necessary 1
Differential Diagnosis
- The differential diagnosis includes metastatic Crohn's disease, which may appear as solitary or multiple nodules, plaques, ulcers, or violaceous perifollicular papules 1
- Histology of erythema nodosum reveals a non-specific focal panniculitis, while metastatic Crohn's disease is characterized by non-caseating granulomas 1
From the Research
Physical Exam Appearance of Erythema Nodosum
The appearance of erythema nodosum on physical exam is characterized by:
- Tender, erythematous, subcutaneous nodules that are typically located symmetrically on the anterior surface of the lower extremities 2, 3, 4, 5, 6
- Nodules are usually rounded or oval, slightly raised, and nonulcerative, measuring 1 to 6 cm in diameter 4
- Lesions are often accompanied by fever and may be preceded by arthralgia 5
- The nodules may exhibit a range of colors, including bright red, livid red, purplish, yellow, or greenish, taking on the appearance of a deep bruise 2
- Ulceration is never seen, and the nodules heal without atrophy or scarring 2, 3
Typical Locations of Erythema Nodosum
Erythema nodosum typically occurs on the:
- Anterior aspects of the lower extremities 2
- Shins, ankles, and knees 2
- Extensor surface of the lower legs 5
- Lower parts of the thighs and forearms (less common) 4
Clinical Variants of Erythema Nodosum
Some clinical variants of erythema nodosum have been described, including: