Tender erythematous nodules or plaques on the extensor surfaces—usually on the legs and occasionally on the arms—are the hallmarks for erythema nodosum, which was diagnosed in this case. It typically occurs in young women, ages 15 to 30, and the nodules or plaques are often accompanied by prodromal fever and malaise. The lesions often are painful and tender to pressure or palpation; they are thought to be caused by a reaction to a stimulus, leading to inflammation of the septa in the subcutaneous fat. While the trigger is often unknown, in some cases, an underlying infection, particularly Streptococcus or tuberculosis (TB), is identified. Sarcoidosis, malignancy, or an increase in estrogen (exogenous or endogenous) also can provoke the disorder.
Due to the risk of underlying disease or triggers, it is prudent to perform radiography of the chest, as well as obtain a complete blood count, sedimentation rate or C reactive protein, and an antistreptolysin O titer when you suspect erythema nodosum. TB testing is also advised. Biopsy typically is not performed because the diagnosis usually is made clinically. If the diagnosis is in doubt, a biopsy can offer confirmation or lead to a different diagnosis such as vasculitis—especially if the lesions are eroded. Since erythema nodosum is an inflammation of the subcutaneous fat, it is important to sample skin lesions deeper than the usual punch biopsy; an incisional biopsy may be required to get an adequate sample.
Erythema nodosum typically resolves spontaneously over a period of weeks, even if there is underlying disease. Therefore, it may be possible to defer treatment if minimal symptoms are present. Otherwise, first-line treatment for the pain and malaise is a nonsteroidal anti-inflammatory drug (NSAID). Oral potassium iodide (360-900 mg/d) is considered second-line treatment and systemic corticosteroids are a third-line option.
For this patient, biopsy was deferred and diagnostic tests were all negative. She had notable pain and a history of good resolution of symptoms with prednisone (5 mg/d), so this drug was prescribed for a 7-day course. She was counseled to avoid taking the NSAIDs and prednisone together due to increased risk of gastritis and ulceration. Recurrent disease can be treated with dapsone (100 mg/d) or hydroxychloroquine (200 mg bid).
Photo and text courtesy of Daniel Stulberg, MD, FAAFP, Department of Family and Community Medicine, University of New Mexico School of Medicine, Albuquerque.