Erythema Nodosum

This blanching, erythematous, maculopapular,
confluent rash on the shins of an 8-year-old girl began as a few red spots 2 weeks earlier and had progressively worsened and become painful. A week before presentation, the child had been treated for pharyngitis. She had full range of motion in both legs without joint pain or swelling.

Results of a complete blood cell count (CBC), measurements of electrolyte concentrations, and urinalysis were normal. A rapid streptococcal test result was negative. The C-reactive protein level was elevated at 3.3 mg/L (normal, less than 1 mg/L); the erythrocyte sedimentation rate was 58 mm/h (normal, 4 to 20 mm/h).

Erythema nodosum (EN) was diagnosed. This
disorder is the most common inflammation of subcutaneous fat.1 Miescher granuloma—a small, well-defined, nodular aggregation of histiocytes arranged radially around a variably shaped central cleft—is its histopathological hallmark.² Between 1 and 5 persons per 100,000 are affected; the peak incidence is between 20 and 30 years of age. The male-to-female ratio is 1:1 in children but 1:2 in adults.

The rash may be preceded by a 1- to 3-week prodrome of weight loss, malaise, low-grade fever, cough, and arthralgia with or without arthritis.¹ The eruption usually presents as symmetrical, tender, erythematous, warm nodules with raised plaques.2 Pretibial involvement is most common; however, the extensor surfaces of the forearms, thighs, and trunk can also be affected.

The history helps guide the evaluation, which may include CBC, sedimentation rate, antistreptolysin O titer, urinalysis, throat culture, intradermal tuberculin test, and chest radiography to exclude an underlying cause. EN is associated with infections (ß-hemolytic streptococcal infection, Yersinia infection, tuberculosis, and leprosy), drugs (antibiotics and hormonal contraceptives), chronic inflammatory diseases (sarcoidosis, Behçet syndrome, and inflammatory bowel disease), and malignancy (lymphoma and leukemia).³ The frequency of EN in different diseases varies with the population studied. The likely cause in this patient was streptococcal pharyngitis.

The nodules of EN are self-limited and heal without scarring. The goal of treatment is to manage any underlying condition. Bed rest, elevation, compressive bandages, NSAIDs and corticosteroids, and avoidance of contact irritation can relieve symptoms.¹