The necrobiotic disease
granuloma annulare was studied with the electron microscope in an effort to develop a theory for the mechanism of development of necrobiotic connective tissue. That mechanism must provide for the disappearance of nuclei, the tinctorial change in
collagen, and the retention of connective tissue outlines characteristic of
necrobiosis. Our observations suggest that
necrosis of histiocytes and fibroblasts with release of lysosomal
enzymes is an important early event in the development of
necrobiosis. Increased quantities of extracellular
hyaluronic acid are also present in the earliest recognizable lesions. The combination of lysosomal
enzymes and abundant
hyaluronic acid in the interstitium results in swelling of
collagen. Necrotic cellular debris is deposited about many
collagen fibrils. This material seems to protect
collagen from further destruction and may account for the preservation of connective tissue outlines observed at the light microscopic level. Some
collagen fibrils not protected by cellular debris appear to be disrupted into constituent filaments. Crossbanded filamentous aggregates that resemble fibrous long spaced
collagen were also observed and may represent an abnormal reassembly of disrupted
collagen.