Lack of circulating immune complexes in uncomplicated erythema nodosum.

There is conflicting evidence in the literature concerning the role of circulating immune complexes (CIC) in the pathogenesis of erythema nodosum (EN). We investigated the possible involvement of CIC in 20 patients with EN, the majority of whom had idiopathic or uncomplicated disease. Immune complexes were detected by 3 complementary radioimmunoassays (the Clq, the mRF, and the anti-C3 solid phase assays). During the presence of the skin lesions, the only abnormalities noted were elevated concentrations of CIC detected by the anti-C3 assay in 5 of the 20 patients. None of the patients had elevated CIC by any of the 3 assays after resolution of skin lesions. These observations do not support a significant role for CIC in the pathogenesis of idiopathic or uncomplicated EN.