Biofilms have been found in many cutaneous diseases and play an important role in disease pathogenesis of atopic dermatitis, psoriasis, and tinea versicolor. Recently, necrobiotic granulomas in granuloma annulare were shown to contain biofilms, which led us to investigate whether biofilms are also present in the necrobiotic granulomas of rheumatoid arthritis (RA). In this brief report, we evaluated eight skin nodules from five patients with known rheumatoid arthritis. We used pathology staining to identify two key components of biofilms: polysaccharides (using periodic acid Schiff [PAS] and colloidal iron [CFe]) and amyloid (using Congo Red). We also used the
immune histochemical stain CD 282 to evaluate whether Toll-like receptor 2 was present. The PAS, CFe, and Congo red stains were positive, indicating biofilms were present. CFe positivity is an indicator that the biofilms have an acidic matrix; gram negative organisms are known to thrive in that milieu. CD 282 was negative except in one lesion that was penetrating through the epidermis and one which was weakly positive. Since microbes are responsible for creating biofilms, our findings suggest that microbes, especially gram negatives, are involved in RA pathogenesis.