Generalized granuloma annulare: histopathology and immunopathology. Systematic review of 100 cases and comparison with localized granuloma annulare.

Some form of collagen alteration (necrobiosis) was observed in 53% of patients with generalized granuloma annulare and in 79% of patients with localized granuloma annulare. Fragmentation of collagen bundles was the most common single type of collagen abnormality in both groups. Collagen sclerosis, accompanied by a strong palisading pattern of histiocytes, was more frequent in localized granuloma annulare. Results of microdroplet lipid staining were positive in 80% of annulare cases and 39.3% of nonannulare cases of generalized granuloma annulare. Inflammatory cells were confined to peripheral perivascular lymphocytes; bandlike granuloma below the epidermis was observed. Positive results of direct immunofluorescence tests in 12 of 23 patients with generalized granuloma annulare suggested that fibrin deposition in areas of altered collagen is less frequent in the generalized than in the localized form, a possible reflection of the lower rate of histologic collagen alteration in that group. Lymphohistiocytic granuloma with various degrees of collagen degeneration, microdroplet lipid accumulation, and mucin deposition form the basic pathologic description of granuloma annulare.