Erythema the nodose is the most common form of panniculitis. Typically presented as tender, erythematous, subcutaneous nodules and plates, which arises in crops most commonly in the pretibial areas bilaterally.
Histology of erythema nodosum
Erythema nodosum histologically it represents the prototype of a septal panniculitis. The classic histopathological presentation of erythema nodosum is that of septal panniculitis with a mixture cellular infiltrate of lymphocytes, histiocytes, giant cellsand occasionally eosinophils and a characteristic absence of vasculitis (Figures 1-3).
Miescher radial granulomas consisting of small nodules composed of spindle to oval-shaped histiocytes arranged around minute grooves are thought to be a relatively specific finding for erythema nodosum (Figure 4).
Early lesions can be difficult to diagnose based on histopathologic features alone. Sections can display edematous septa containing a prominent mixed inflammatory infiltrate and minimal fibrosis. As the lesions progress, there is neutrophilic infiltration followed by chronic infiltrators, granulomas and septal fibrosis.
Small-vessel vasculitis (or venulitis) may be seen in early lesions.
Pathology of erythema nodosum
Figure 1
Figure 2
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Figure 4
Special studies for erythema nodosum
Generally none is needed. Heavy neutrophilic infiltrates can cause staining for microorganisms.
Differential diagnosis of erythema nodosum
Early lesions may resemble those of neutrophils. skin disease.
Late lesions may resemble other causes of sclerosis of the subcutis, including fat resolution necrosis, dermatitis artefacta and lipodermatosclerosis.
Miescher's radial granulomas have also been described in erythema induratus, necrobiosis lipoid, sweet syndrome and Behcet's disease.
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