Pathology
Erythema nodosum represents an inflammation of the septa in the subcutaneous adipose tissue (a septal paniculitis)
Evidence suggests that erythema nodosum develops as a type IV delayed hypersensitivity response to a number of antigens e.g. - streptococcal infection, tuberculosis, fungal infection, leprosy and some drugs.
The histopathology is distinctive:
- early lesions show widening of the connective tissue between lobules and may be associated with haemorrhage
- a characteristic finding of the disease is Actinic (Miescher's) radial granulomas – these are well demarcated, small, nodular collections of tiny histiocytes around a central stellate cleft
- later there is an cellular infiltrate containing lymphocytes, histiocytes and multinucleate giant cells
Reference:
- Pérez-Garza DM, Chavez-Alvarez S, Ocampo-Candiani J, et al. Erythema nodosum: a practical approach and diagnostic algorithm. Am J Clin Dermatol. 2021 May;22(3):367-78.
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