Non-Neoplastic Dermatopathology

5.3

E RYTHEMA NODOSUM VS TRAUMATIC PANNICULITIS

Erythema Nodosum

Traumatic Panniculitis

Age

Any age; most commonly between 25 and 40 years of age; women more often than men. Extensor surfaces of legs and knees; less commonly on thighs, arms, calves, and face. Delayed-type hypersensitivity due to exposure to a variety of antigens. Underlying causes include infection, medications, malignancy, inflammatory bowel disease, and other inflammatory processes. Between 30% and 50% of cases are idiopathic. Abrupt onset of tender, erythematous, nonulcerated, fixed nodules on bilateral shins. May have prodrome of fever, fatigue, and arthralgias. 1. Septal panniculitis with edema and mixed inflammatory infiltrate (Figs. 5.3.1 and 5.3.2) . 2. Inflammation includes lymphocytes, histiocytes, neutrophils, and eosinophils (Fig. 5.3.2) . 3. Noncaseating granulomas including Miescher radial granulomas characterized by macrophages surrounding cleft-like spaces with or without clusters of neutrophils (Fig. 5.3.3) . 4. Septal fibrosis with slight extension of inflammation into fat lobules (Figs. 5.3.1 and 5.3.2) . 5. No significant fat necrosis or calcification. PAS or GMS and AFB stains to exclude fungal and mycobacterial infection. Treatment is not generally necessary but nonsteroidal anti-inflammatory agents and potassium iodide may be used for symptomatic relief. Intralesional or systemic glucocorticoids are alternative therapies for nonresponsive cases. Nodules spontaneously resolve within 2 months but may have postinflammatory hyperpigmentation.

Any age.

Location

Any site but most commonly involves shins, forearms, and breasts.

Etiology

Blunt trauma in fatty zones.

Presentation

Indurated, erythematous subcutaneous plaques or nodules. Hypertrichosis has been reported in some cases. 1. Normal epidermis and dermis. 2. Lobular infiltrate of histiocytes, including foamy histiocytes and giant cells, surrounding fat microcysts (lipophagic fat necrosis) (Figs. 5.3.5 and 5.3.6) . 3. Microcysts vary in size and shape (Fig. 5.3.5) . 4. Lipomembranous change with variable fibrosis and dystrophic calcification (Fig. 5.3.6) . Lipomembranous change consists of feathery eosinophilic material at the periphery of cystic spaces. 5. Fibrosis may form a capsule around the fat necrosis (Fig. 5.3.4) .

Histology

Special studies

None.

Treatment

Symptomatic treatment only.

Self-limited disorder. May recur in individuals susceptible to repeat trauma. Copyright © Wolters Kluwer, Inc. Unauthorized reproduction of the content is prohibited. 2023

Prognosis

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