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A young woman presented to the office with several days of overall malaise, fever, and sore throat. At the time of presentation she noted some painful bumps on her lower legs, and denied trauma (Figure 178-1). No history of recent cough or change in bowel habits has been reported. The patient had no chronic medical problems, took no medications and had no known drug allergies. Her temperature was slightly elevated, but other vitals were normal. On examination, her oropharynx revealed tonsillar erythema and exudates. Bilateral lower extremities were spotted with slightly-raised, tender, erythematous nodules that varied in size from 2 to 6 cm. Rapid strep test was positive and she was diagnosed clinically with erythema nodosum (EN) secondary to group A β-hemolytic Streptococcus. She was treated with penicillin and NSAIDs, and was advised temporary bedrest. She experienced complete resolution of the EN within 4 weeks.

Figure 178-1

Erythema nodosum secondary to group A β-hemolytic Streptococcus in a young woman. (Courtesy of Richard P. Usatine, MD.)

EN is a common inflammatory panniculitis characterized by ill-defined, erythematous patches with underlying tender, subcutaneous nodules. It is a reactive process caused by chronic inflammatory states, infections, medications, malignancies, and unknown factors.

Lofgren syndrome (with hilar adenopathy).

  • Erythema nodosum occurs in approximately 1 to 5 per 100,000 persons.1 It is the most frequent type of septal panniculitis (inflammation of the septa of fat lobules in the subcutaneous tissue).2
  • EN tends to occur more often in women, with a male-to-female ratio of 1:4.5 in the adult population, generally during the second and fourth decades of life (Figures 178-1, 178-2, and 178-3).3
  • In 1 study, an overall incidence of 54 million people worldwide was cited in patients older than 14 years of age.4
  • In the childhood form, the female predilection is not seen.

Figure 178-2

EN in a middle-aged woman around the knee secondary to sarcoidosis. (Courtesy of Richard P. Usatine, MD.)

Figure 178-3

EN in a middle-aged woman with no known cause. These lesions are bright red, warm, and painful. (Courtesy of Hanuš Rozsypal, MD.)

  • Most EN is idiopathic (Figures 178-3 and 178-4). Although the exact percentage is unknown, 1 study estimated that 55% of EN is idiopathic.5 This may be influenced by the fact that EN may precede the underlying illness. The distribution of etiologic causes may be seasonal.6 Identifiable causes can be infectious, reactive, pharmacologic, or neoplastic.
  • Histologic examination is most useful in defining EN. Defining characteristics of EN are a septal panniculitis without presence of vasculitis. That this pattern develops in certain areas of skin may be linked ...

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