Granuloma annulare: histopathologic and direct immunofluorescent study.

Eighteen cases of granuloma annulare were classified histopathologically and examined by direct immunofluorescence. The three different histopathologic types of granuloma annulare were compared with the result of immunofluorescence examination. No features of leukocytoclastic vasculitis were seen. Direct immunofluorescence of granuloma annulare does not reveal any consistent diagnostic pattern. Dermal desposition of fibrin in necrobiotic areas were noted in 8 cases of 18. Blood vessel and/or basement membrane deposition of IgM and C3 was inconsistent and does not support an immune complex vasculitis. Direct immunofluorescence is useful in studying the pathogenesis of granuloma annulare. The finding of fibrin, together with the histology, suggests to us a delayed hypersensitivity reaction as the dominant pathogenic event.