Part of “CHAPTER 66 – RARE DISORDERS OF SKELETAL FORMATION AND HOMEOSTASIS“

Fibrogenesis imperfecta ossium is a sporadic, idiopathic disorder in which pathologic changes seem to affect collagen within the skeleton only. Symptoms begin in adult life. There is progressive pain, recurrent fractures, and then weakness, muscle atrophy, and contractures. Patients become immobilized and debilitated. Marked bone tenderness is elicited by palpation. Serum calcium and phosphate levels are unremarkable, although alkaline phosphatase activity may be increased. Radiographic abnormalities occur throughout the skeleton, except the skull.5 Although generalized osteopenia (most marked in the axial skeleton and periarticular regions) with a paucity of spongy bone is present, trabeculae appear coarse and dense. An abnormal trabecular pattern replaces cortical bone. Deformity secondary to fracture may be present, but bony contours are usually normal. Vertebral end plates can appear sclerotic and mimic a “rugger-jersey” spine. The radiographic differential diagnosis includes advanced osteitis fibrosa
cystica, Paget bone disease, and axial osteomalacia.5 Histopathologic studies are important and show that the birefringent pattern normally formed by collagen fibrils is absent in lamellar bone. Electron microscopy reveals a random, tangled pattern of thin collagen fibrils.83 Increased numbers of osteoid seams do not take up tetracycline labels. The pathogenesis seems to involve a defect in bone matrix rather than in mineral metabolism. No effective medical therapy is known.