Clinical Manifestations of Erythema Nodosum
Erythema nodosum presents as raised, tender, red or violet subcutaneous nodules of 1–5 cm in diameter, characteristically located bilaterally on the extensor surfaces of the extremities, particularly the anterior tibial areas. 1
Primary Cutaneous Features
The skin lesions have distinctive characteristics that evolve over time:
- Nodule appearance: Round or oval, slightly raised, non-ulcerative painful nodules ranging from 1-6 cm in diameter, sometimes coalescing 2
- Color evolution: Initially bright red, progressing to livid red or purplish within days, and finally exhibiting a yellow or greenish appearance resembling a deep bruise 3
- Distribution: Symmetrical and bilateral, predominantly on shins, ankles, and knees 1. Can also involve the trunk, upper extremities, thighs, forearms, neck, and arms, though less commonly 1, 2
- Surface characteristics: Never ulcerate and heal without atrophy or scarring 3
Associated Systemic Manifestations
EN frequently presents with systemic symptoms that may precede or accompany the skin lesions:
- Arthralgia and arthritis: Occurs in 64-70% of cases, typically involving multiple joints symmetrically, more commonly affecting distal lower extremities 1, 4, 5
- Constitutional symptoms: Fever (present in 60% of cases), malaise (67%), fatigue, and occasionally chills 1, 4, 5
- Timing: Usually occurs during times of underlying disease activity, particularly in inflammatory bowel disease 6
Diagnostic Considerations
A firm clinical diagnosis can normally be made based on the characteristic appearance and distribution, with biopsy reserved for atypical cases. 1 When performed, histology reveals non-specific focal panniculitis—specifically a septal panniculitis without vasculitis, with thickened septa infiltrated by inflammatory cells extending to periseptal areas 3.
Important Clinical Pitfalls
The differential diagnosis must exclude metastatic Crohn's disease, which can appear as solitary or multiple nodules, plaques, ulcers, or violaceous perifollicular papules at any site, with non-caseating granulomas on histology 1. This distinction is critical as management differs significantly.
Tissue hypersensitivity is characteristically pronounced at sites of trauma and at sites of specific skin testing 5, which can help distinguish EN from other conditions.
The prevalence of EN in inflammatory bowel disease ranges from 4.2-7.5%, occurring more frequently in Crohn's disease than ulcerative colitis, and is more common among female patients 1.