Background: Erythema nodosum (EN) is a condition characterized by the presence of painful erythematous nodules on the pretibial aspects of the lower extremities. EN is thought to be a local inflammatory, immune-mediated reaction to a number of systemic antigenic stimuli. This condition is noted most often in women between menarche and menopause and is associated with certain drugs, infections, and pregnancy. However, no reports in the literature describe EN as a result of streptococcal infection during pregnancy.Case: A 21-year-old, white woman, G3P0020, presented at 13 weeks gestation with a 2-week history of erythematous, tender lesions on the pretibial aspects of both legs consistent with EN. The patient reported having had a “flu-like” illness at the same time the lesions developed. The “flu” symptoms resolved within 10 days without medical intervention, but the lesions on her legs persisted. An initial antistreptolysin-O (ASO) titer was elevated at 960 Todd units (normal values: preschool and adults <85; school-age and young adults <170). Six days later, she presented to the emergency department with complaints consistent with a urinary-tract infection. She was empirically treated with a 10-day course of amoxicillin, 500 mg t.i.d. Although the patient was treated with amoxicillin for a presumed urinary-tract infection (which was culture-negative), the lesions resolved after her completion of the antibiotics. Twelve weeks later, a repeat ASO was within normal limits. The EN lesions did not recur.Conclusion: Although many etiologic factors are identified as causes of EN, the condition is usually self-limiting, requiring only minimal supportive measures until it resolves. A careful history should be obtained and a physical examination performed to exclude other causes. If a recent streptococcal infection is identified or presumed, a 10- to 14-day course of antibiotics is warranted.
