Erythema nodosum

Erythema nodosum (EN) has been known since 1798,¹ when it was considered to be a clinical entity. In the latter half of the 19th century, “rheumatism” was regarded as the principal cause and tuberculosis as a minor causative factor of EN. During the first four decades of the present century, tuberculosis was reported to be the cause of EN in over 90% of adult patients, but in the 1940s and 50s, sarcoidosis, streptococcal, and other infections, and some other causes, were suggested.² During the last 15–20 years, a variety of factors have been found to trigger EN; however, despite thorough investigations, no evident cause for EN can be found in 10–30% of cases (Fig. 1).