Objective: To examine the HLA-DRB1 associations of patients with erythema nodosum (EN), establish HLA-DRB1 differences among patients with idiopathic and secondary EN, and identify the HLA-DRB1 associations with specific conditions presenting with EN.
Methods: We conducted a retrospective study of 100 patients (83 women) with biopsy proven EN diagnosed for a defined population in Northwest Spain. Patients were classified into idiopathic or secondary if skin nodules occurred in the context of a well defined disease, or there was a precipitating event in close temporal relationship with the onset of EN. Patients and controls were HLA-DRB1 genotyped from DNA using molecular based methods.
Results: At the time of diagnosis no precipitating events or underlying diseases were identified in 35 cases and, due to this, they were considered to be idiopathic. Although strong associations do not appear to exist between HLA-DRB1 and unstratified EN, the idiopathic group showed a significantly lower frequency of HLA-DRB1*04 phenotype compared with controls. Among the patients with secondary EN, the patient subgroup with sarcoidosis exhibited a significantly increased frequency of HLA-DRB1* 13 compared with healthy controls.
Conclusion: Idiopathic and some groups of secondary EN seem to have different HLA-DRB1 associations. These differences may have prognostic value in identifying patients with specific conditions associated with this syndrome.