Necrobiosis lipoidica: ultrastructural and biochemical demonstration of a collagen defect.

Ten patients with necrobiosis lipoidica lesions were studied. Five patients had diabetes mellitus. The age of the patients varied from 15 to 73 years and the duration of the skin lesions was from 2 to 20 years. Histologically, the lesions were characterized by degeneration of collagen and elastin. In some lesions elastin fibers could be seen in areas devoid of normal-looking collagen. Electron microscopy revealed loss of cross-striation of collagen fibrils and a marked variation in the diameter of individual collagen fibrils. The concentration of collagen, measured by assay of hydroxy-proline, a collagen-specific amino acid, was markedly decreased in the lesional skin, but the ratio of type I/III collagen was unchanged in the affected skin. Fibroblasts established from affected skin synthesized less collagen than cells derived from healthy-looking skin. The decreased collagen synthesis was due to a decreased amount of messenger RNA for type I procollagen, measured by hybridization with a specific human cDNA clone. The production of collagenase by these fibroblasts was not increased. Our results thus indicate that in necrobiosis lipoidica lesions, collagen fibrils are defective and the amount of collagen is reduced, probably due to decreased synthesis of collagen by affected fibroblasts.