Bone remodeling disorders

Paget s disease is a chronic bone disorder characterized by abnormal bone remodeling. The disease disrupts the growth of new bone tissue causing the bone to thicken and become soft. This weakens the bone, which increases susceptibility of fracture even with slight trauma or collapse of the bone (eg, the vertebrae). 

Mundy, G.R. 1999. Bone remodeling. In Primer on the Metabolic Bone Diseases and Disorders of Mineral Metabolism (M J. Favus, ed.), pp. 30-38. Lippincott Williams Wilkins, New York. 

Paget s disease is a localized disorder of bone remodeling characterized by the development of deformations and changes in the shapes, sizes and directions of the diseased bones, such as the skull, spine, arms, and legs [13]. 

Figure 49-1 Bone remodeling.The bone remodeling sequence includes activation, reversal, formation, and resting phases. Reproduced from Baron R 2003 General Principles of Bone Biology. In Favus M (ed.) The Primer on the Metabolic Bone D/seoses and Disorders of Mineral Metabolism, 5th ed. American Society for Bone and Mineral Research, Washington DC, USA, pp. I 8 with permission of the American Society for Bone and Mineral Research.

Bone tissue is constantly being renewed by the concerted action of osteoblasts and osteoclasts. Bone remodeling has two main phases a resorption phase consisting in the removal of old bone by osteoclasts, and a later phase of new bone formation driven by osteoblasts [6], Thus, the activity of osteoblasts and osteoclasts determines bone mass, bone geometry, bone quality, and, subsequently, bone strength [7, 8]. Osteoporosis is a prevalent disorder consisting in decreased bone mass and/or abnormal bone microarchitecture that impairs bone strength and increases the risk of fracture. Therefore, patients with osteoporosis may suffer fractures as a result of minor trauma, or even in the absence of trauma. The most common osteoporotic fractures are those of the vertebral bodies, the hip, the wrist, the shoulder, and the pelvis. 

Calcitonin is used in the treatment of Paget s disease (osteitis deformans), a chronic disorder characterized by increased bone remodeling, normocalcemia and normophosphatemia, frequent episodes of hypercalciuria leading to stone formation, and elevation of serum alkaline phosphatase and urinary hydroxyproline levels. The disease does not appear to be primarily a derangement of calcium metabolism. Calcitonin reduces the levels of serum alkaline phosphatase and urinary hydroxyproline, and may relieve other symptoms of the disease as well. Diphosphonates, especially etidronate disodium, also reduce bone resorption in this disease. Various cancers are accompanied by hypercalcemia and may respond to treatment with calcitonin. 

Definition localized disorder of bone remodeling, resulting in excessive bone resorption followed by disorganized bone replacement, producing thickened but weak bone that is susceptible to deformity and fracture... 

Crosbie, O.M., Freaney, R., and McKenna, M.J. 1999. Bone density, vitamin D status, and disordered bone remodeling in end-stage chronic liver disease . Calcified Tissue International, 64 295-300. 

Disorders of bone Bisphosphonates, calcitonin, estrogen, calcitonin, remodeling calcium, fluoride, PTH + vitamin D... 

Paget s disease of the bone is a metabolic bone disorder in which one or more of the bones undergo continuous dysregulated remodeling [6, 17]. Hyperactivation of osteoclasts in the affected bones leads to improper resorption of bony tissue, followed by a compensatory overproduction of poorly formed bone by osteoblasts. This typically results in both osteoporosis and bone deformation, and can lead to frail, disfigured bones that are prone to fracture [6]. This, coupled with the symptoms of IBM, can lead to greatly diminished mobility of patients with IBMPFD. 

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