Osteogenesis imperfecta.

Abstract

Osteogenesis imperfecta or fragilitas ossium has been described since the 18th century. It was given its present name of osteogenesis imperfecta by Vrolik in 1849. This is a disease which involves the tissues developing from the primitive mesenchyme. The characteristic feature is brittleness of the bones, with varying numbers of fractures, often following slight trauma. The condition is seen at all ages, chiefly in the infant, and often in utero. Various types have been recognized by different observers. The most common are the non-hereditary congenital type, which appears in utero or at birth, and the hereditary type. In the non-hereditary type the sclerae may be blue or white, and characteristic roentgen changes are present in either event. The hereditary type may also be associated with either blue or white (rare) sclerae with a characteristic roentgen picture, or with blue sclerae and atypical roentgen findings. The cases have been classified also according to the age at which the disease is recognized, that is, fetal cases, infantile cases, adolescent cases, and late cases. Pathology The underlying pathological process appears to be deficient osteogenesis; in the more severe congenital forms there is some resemblance to the changes found in infantile scurvy. The most marked deformities are in the long bones. These are slender, the cortex is thin, and the trabecu-lae are rudimentary. The periosteum is thin, while marrow spaces are enlarged. Fractures are often subperiosteal, without displacement, and callus formation follows promptly. On section, the shafts are soft. The epiphyses may be relatively normal until late in the disease, when degenerative changes may appear. Microscopic sections reveal complete loss of the normal bony structure, with the haversian canals appearing as wide spaces interspersed with embryonal and osteoid tissue. The bony lamellae are lacking. Fibroblasts, chondroblasts, and transitional cells replace osteoblasts. Sections taken through an area of callus may reveal cartilaginous tissue with extensive areas of necrosis. In the diaphyseal portion of the bone necrotic areas are seen. Roentgen findings Skull: The visible bone appears to be made up of isolated islands. Early in the course of the disease the suture lines are difficult to delineate ; later they are marked by the development of wormian bones, especially in the lambdoid and coronal sutures. Increase in the bitemporal diameter of the skull is common. It is almost impossible, however, to differentiate the skull changes in osteogenesis imperfecta from those of cleidocranial dysostosis. Long Bones: The characteristic findings in the long bones are a thin cortex and a large medullary cavity. Osteoporosis may be more severe in the lower extremities than in the upper. At a later age some of this may be due to atrophy of disuse. Many of the epiphyses present a foamy appearance.