Erythema Nodosum (EN)

Erythema nodosum (EN) is an inflammation of the subcutaneous fat  characterized by  painful, red swellings over the shins. The eruption may also involve the extensor aspects of the thighs and forearms. The condition is believed to be a delayed hypersensitivity reaction and occurs most often in women during their reproductive years [2, 3].  Erythema nodosum migrans, subacute nodular migratory panniculitis, and chronic erythema nodosum, are considered to be variants of the same disease [1].

Excisional biopsy of the lesions in the early stages of EN shows a perivascular infiltrate of neutrophils   in the interlobular septa that is sub-sequently replaced by lymphocytes, and a granulomatous infiltrate with giant cells. Small histiocytes, radially placed around a central cleft, Miescher's radial granulomas, are a characteristic finding. 

EN may be associated with a  variety of systemic diseases or medications. However, an identifiable cause is not found in about 50% of patients.  The most common identifiable causes of EN are streptococcal infection and sarcoidosis [1-5].

Conditions Associated with Erythema Nodosum

Common [1 -16]
 

Initial evaluation shouldincludes:

• Throat culture>
• Antistreptolysin-O (ASO) titer
• CBC
• Erythrocyte sedimentation rate , ESR
• Intradermal skin tests for tuberculosis and coccidioidomycosis
• Chest film to evaluate for hilar adenopathy.
• In patients with GI symptoms obtain stool culture to include Yersinia enterocolitica (consider serological testing also).
• Consultation with a dermatologist and/or internist for evaluation of underlying cause of EN may be helpful.

Other conditions to consider in the differential diagnosis include alpha-1 antitrypsin deficiency panniculitis, lupus panniculitis, cutaneous polyarteritis nodosa, superficial thrombophlebitis , and erythema induratum.

Clinical Course

EN typically presents as multiple, tender, bright red, 1 to 20 cm in diameter,  poorly demarcated nodules on the shins (usually bilateral). The eruption may also involve the extensor aspects of the thighs and forearms. Over the course of 2 weeks the the lesions  change in color to a bluish hue, and then fade to resemble a bruise. Ulceration and scarring does not normally occur. Ankle swelling and joint pain are common and usually resolve within a few weeks. However,  joint pain has been reported to persist for up to 2 years [4]. Pulmonary hilar adenopathy may also develop.

Prodromal symptoms of fatigue and malaise or upper respiratory tract infection often precede the eruption by 1 to 3 weeks. In a study by Metz and coworkers patients with fever, leukocytosis, elevated CRP level ( 6 X upper limits), accelerated ESR, presence of cough, sore throat, diarrhea, arthritis, and pulmonary pathology  were more likely to have EN secondary to an identifiable cause [2].

EN is characteristically self limited and resolves on its own in 3 to 6 weeks. Adverse effects upon the course of pregnancy or fetal outcome would not be expected in idiopathic cases [8]. Underlying causes of EN that might result in increased morbidity or mortality in the mother or fetus should be excluded.