Erythema nodosum: etiologic and predictive factors in a defined population.

OBJECTIVE

To examine the frequency and features of erythema nodosum (EN), establish disease associations, and identify the optimal set of predictors for the occurrence of secondary EN.

METHODS

We performed a retrospective study of an unselected population of patients 14 years and older with biopsy-proven EN diagnosed at a referral hospital between 1988 and 1997. Patients were classified as having either idiopathic EN or EN secondary to other diseases if the skin nodules occurred in the context of a well-defined disease, or if there was a precipitating event in close temporal proximity to the onset of EN.

RESULTS

One hundred six patients (82 women) were diagnosed as having biopsy-proven EN. At the time of diagnosis, no precipitating events or underlying diseases were identified in 36.8% of patients. Sarcoidosis and nonstreptococcal upper respiratory tract infections (URI) were the most common conditions associated with secondary EN. Only 1 of 35 patients with an initial diagnosis of idiopathic EN and a followup of at least 1 year was finally diagnosed as having secondary EN. The best predictive model of secondary EN included an abnormal results on a chest radiograph, a previous history of nonstreptococcal URI, and a significant change in antistreptolysin O (ASO) titer in 2 consecutive determinations performed in a 2-4-week interval. Also, the presence of peripheral synovitis, a positive tuberculin skin test, and a history of diarrhea suggested the presence of secondary EN. This model showed high sensitivity and specificity.

CONCLUSION

Idiopathic EN is common. A basic procedure including careful medical history-taking, a physical examination for peripheral synovitis, 2 consecutive ASO determinations, a tuberculin skin test, and chest radiography may be sufficient to diagnose EN.