Erythema Nodosum and Hematoma Presentation
Erythema nodosum does not typically present with hematoma, as the lesions are inflammatory nodules that may evolve in appearance but do not represent true hematomas.
Clinical Presentation of Erythema Nodosum
Erythema nodosum (EN) presents with characteristic features that distinguish it from hematomas:
- Typical appearance: Tender, erythematous, raised subcutaneous nodules, usually 1-5 cm in diameter 1
- Location: Most commonly bilateral and symmetrical on the anterior tibial areas (shins) 1, 2
- Evolution of lesions: Initially bright red, then evolve to livid red or purplish, and finally exhibit a yellow or greenish appearance resembling a bruise 2
- Key distinguishing feature: Lesions do not ulcerate and heal without atrophy or scarring 2
Color Changes vs. True Hematoma
The color changes in erythema nodosum might be confused with hematomas:
- The nodules evolve through a predictable color sequence (red → purplish → yellow/green) that can mimic the appearance of a resolving bruise 2
- This bruise-like appearance is due to inflammatory changes and hemosiderin deposition, not actual bleeding into tissues 2
- Unlike true hematomas, EN lesions remain raised, tender nodules throughout their evolution 1
Histopathological Differences
The histopathology of erythema nodosum clearly differentiates it from hematoma:
- EN is characterized as a septal panniculitis (inflammation of the septa between fat lobules) without vasculitis 2
- Early lesions show edema, hemorrhage, and neutrophilic infiltration in the septa 2
- Later lesions demonstrate fibrosis, periseptal granulation tissue, lymphocytes, and multinucleated giant cells 2
- A hallmark finding is Miescher's radial granulomas (small nodular aggregations of histiocytes arranged radially around a central cleft) 2
Diagnostic Considerations
When evaluating suspected erythema nodosum:
- Diagnosis is primarily made on clinical grounds 3, 1
- In atypical cases, a skin biopsy may be helpful to confirm the diagnosis 3
- Misdiagnosis is common in emergency settings, with EN being confused with cellulitis, infected insect bites, or minor trauma 4
When to Consider Alternative Diagnoses
Consider alternative diagnoses when:
- Lesions are unilateral rather than bilateral
- Actual fluid collection or fluctuance is present
- Lesions ulcerate (never occurs in EN) 2
- Patient has a history of trauma to the area
- Patient is on anticoagulants or has a bleeding disorder 3
Conclusion
While erythema nodosum lesions may evolve to have a bruise-like appearance, they represent an inflammatory process rather than true hematomas. The characteristic clinical presentation, evolution, and histopathological findings distinguish EN from true hematomas. When in doubt, a skin biopsy can provide definitive diagnosis in atypical cases.