Erythema Nodosum

Epidemiology:

• Most common form of panniculitis
• Young women mostly
• Most cases are idiopathic
• associated conditions:
• infections:
1. beta-hemolytic strep
2. TB
3. Coccidioidomycosis
4. Histoplasmosis
5. Leprosy
• drugs:
1. Sulfonamides
2. Oral contraceptives
• Sarcoidosis
• IBD
• malignancies

Common sites:

• Lower legs

Gross features:

• Poorly-defined erythematous plaques and nodules
• Easier felt than seen
• Exquisitely tender
• Lesions flatten and become bruise-like over weeks
• No ulceration

Histologic features:

• Widening of connective tissue septa (early)
• Edema
• Fibrin exudation
• Neutrophilic infiltration
• Septal fibrosis (later)
• Infiltration by lymphocytes, histiocytes, multinucleated giant cells, occasional eosinophils
• No vasculitis

Immunophenotype:

Marker:

Sensitivity:

Specificity:

Molecular features:

Other features:

• acute presentation
• last several weeks and resolve without sequelae
• fevers, arthralgias
• deep wedge biopsy usually required for definitive diagnosis

References:

• Robbins 2005