Erythema nodosum: etiological factors and relapses in a retrospective cohort study.

Erythema nodosum (EN) is a septal panniculitis which may be associated with a wide variety of factors and disorders. In some patients it is recurrent, but few studies have considered recurrent EN. Our aim was to describe the causes of and diseases associated with EN and relapsing EN. Patients diagnosed with EN from 1997 to 2007 were included. EN was defined as post-infective, based on temporal, clinical, laboratory and microbiological criteria. Diagnosis of drug-induced EN was based on a temporal correlation, on the relapse of EN after drug re-introduction and on the absence of relapsing EN with a continuous treatment with the imputed drug. When the above criteria were excluded and EN was not associated with an underlying systemic disease or pregnancy, it was considered idiopathic.124 patients (mean age 39.5 years; median 37 years; range 4-90 years) were visited and re-evaluated after one to ten years (mean ± SD follow up time 5 ± 4 years). In 73 (58.8%) patients an aetiology of the first manifestation of EN was attributed to infections (25.8% of the total number; 32% of those with an attributed aetiology), drugs (mostly sex hormones; 15.3%; 26%), systemic diseases (11.2%; 19.2%) and pregnancy (6.5%; 10.9%). EN relapsed in 33 (26.6%) patients and was mostly attributed to infections and drugs. Factors responsible for the first manifestation of EN frequently differed from those causing relapses in the same patients, with the exception of drug-induced EN. We conclude that drug-induced EN can recur after re-exposure to the same drug, and the recurrence can be predicted.