Histologic, ultrastructural and histochemical studies of granuloma annulare.

We reviewed and reclassified the histology in 207 cases of granuloma annulare from our files. The most common pattern found was mononuclear infiltrative type (72%) in contrast to the palisading group (25%) and the epithelioid nodules (3%). Indeed, and entire spectrum from mononuclear infiltrates to the epithelioid sarcoidal types is seen. The electron microscopic findings include histiocytes with membrane activity, well-developed rough endoplasmic reticulum, large mitochondria, and numerous lysosomes. Pathcy damage of collagen and elastic fibers with the presence of vesicles, lysosomes, and cytoplasmic debris are demonstrated. The histochemical and ultrastructural studies localized acid phosphatase in the primary lysosomes and the routh endoplasmic membrane. The presence of fibrin deposition confirmed our previous immunofluorescence results.