Fibromatosis hyalinica multiplex (juvenile hyalin fibromatosis) light microscopic, electron microscopic, immunohistochemical, and biochemical findings

Fibromatosis hyalinica multiplex juvenilis (juvenile hyalin fibromatosis) is a very rare mesenchymal dysplasia, probably inherited as an autosomal‐recessive trait. Two nonrelated cases are reported. Among the clinical features, the most impressive lesions are multiple slowly growing subcutaneous nodules, hypertrophic gingiva, flexural contractures with joint stiffness and radiolucent bone destructions. Light microscopic examination of the nodules reveals tumor‐like deposits of an amorphous hyaline ground substance with delicate staining properties situated partly between cellular and vascular areas. Ultrastructural characteristics are cystic, dilated rough endoplasmatic reticulum and cystic Golgi vesicles which contain a fine fibrillar material that is also found in the ground substance. Immunohistochemical examination shows collagen type I and type III in the hyaline material, but not type II and type IV. Quantitative biochemical investigation reveals a normal ratio of collagen types I and III.