Pathology of Erythema Nodosum - Dr Sampurna Roy MD

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Pathology of Erythema Nodosum

Erythema nodosum is an acute, nodular, erythematous eruption that usually is limited to the extensor aspects of the lower legs. Erythema nodosum may occur with or without another medical condition. Conditions that are linked with erythema nodosum include drugs (birth control pills, estrogens), strep throat, Cat scratch disease, fungal diseases, infectious mononucleosis, sarcoidosis, Behcet's disease, inflammatory bowel diseases (Crohn's disease and ulcerative colitis), and normal pregnancy.

Erythema nodosum is a disease characterized by painful , erythematous nodular lesions.

It is the most common panniculitis and histologically represents the prototype of a septal panniculitis.

Site:

Situated on the anterior and lateral aspect of the lower extremities and rarely on the arms, trunk, and calves, and on the neck and face.

Age:

Usually occurs in young adults. Cases have been reported in children and in elderly patients.

Pathogenesis:

It is not known and may be due to allergic response to infection or systemic disease.

Erythema nodosum is associated with the following conditions:

- Infection : Streptococcal ;Meningococccal ;Campylobacter ; Salmonella ; Histoplasma ; Mycobacterial ; Dermatophyte ; Yernia.

- Sarcoidosis (2nd most common cause)

- Inflammatory bowel disease ; Behcet disease ; Sweet's disease ; Carcinoma ; lymphoma ; leukemia.

Other triggering factors include drugs (Example: Sulphonamides ; penicillin ; oral contraceptive) and radiotherapy.

Microscopic features:

Septal panniculitis:

Small foci of inflammatory cells extend into adjacent lobular fat ;

Sometimes spillover of cells is prominent and include foam cells ;

There may be focal fat necrosis adjacent to the septa;

Septal infiltrate is composed of lymphoid cells, variable numbers of foreign body giant cells and occasional eosinophils and histiocytes ;

In fully developed lesions granulomas are present in the center of lobules ;

A clue helpful to diagnosis of an early lesion of erythema nodosum is the finding of "radial" granulomas, first described by Miescher and consisting of clusters of neutrophils in collections of epithelioid histiocytes ;

A few neutrophils are present in the early lesion ;

Fibrous septa in the subcutaneous fat are widened by edema ;

Mild to moderate perivascular infiltrate of lymphocytes around vascular plexuses of the reticular dermis ;

Sometimes a definite vasculitis is present (lymphocytic or leukocytoclastic type).

In late lesions septa widened by marked fibrosis ;

Fat lobules are markedly reduced in size by widened fibrotic septa.