Metabolic bone disease or MBD refers to a large spectrum of bone disorders, usually caused by mineral abnormalities such as calcium, phosphorus, magnesium or vitamin D. The most common metabolic bone diseases include osteoporosis, osteomalacia, rickets, renal osteodystrophy and osteitis deformans (Paget?s disease of bone).
Metabolic bone disease can be caused by a number of factors including vitamin D deficiency, hereditary hypophosphatemia, and hyperparathyroidism (over-activation of the parathyroid gland).
The most common form of metabolic bone disorder is osteoporosis. Osteoporosis is a bone disease characterized by a decrease in bone mass and density resulting in brittle, fragile bones that are more susceptible to fractures. The condition most commonly affects elderly women. Osteoporosis related fractures are more common at the hips, wrists, or vertebral bodies of the spine. Osteoporosis is called a ?silent disease,? because a majority of patients are unaware of their condition until they develop a bone fracture.
Metabolic bone disease in children can result in linear growth reduction, bone deformities, non-traumatic fractures, and impairment of motor development and function.
Paget's disease of bone is a chronic disease of the skeleton. In healthy bone, a process called remodeling removes old pieces of bone and replaces them with new, fresh bone. Paget?s disease causes this process to shift out of balance, resulting in new bone that is abnormally shaped, weak, and brittle. Paget?s disease most often affects older people, occurring in approximately 2 to 3 percent of the population over the age of 55.
Many patients with Paget?s disease have no symptoms at all and are unaware they have the disease until x-rays are taken for some other reason. When bone pain and other symptoms are present, they can be related to the disease itself or to complications that arise from the disease?such as arthritis, bone deformity, and fractures.
In most cases, treatment for Paget?s disease involves taking medications to help slow or stop the progress of the disease. For patients who have complications, surgery may be needed to realign deformed bones or to help fractures heal.
Paget's disease can affect any bone in the skeleton. It appears most often in the spine, pelvis, long bones of the limbs, and skull. It can be present in just one bone or in several bones. It can affect the entire bone or just part of it.
In normal bone, a process called remodeling takes place every day. Bone is absorbed and then reformed in response to the normal stresses on the skeleton. More specifically:
In Paget's disease, osteoclasts are more active than osteoblasts. This means that there is more bone absorption than normal. The osteoblasts try to keep up by making new bone, but they overreact and make excess bone that is abnormally large, deformed, and fits together haphazardly.
Normal bone has a tight overlapping structure, like a well-constructed brick wall. Bone afflicted by Paget's disease has an irregular mosaic pattern, as though the bricks were just dumped in place. The end result is bones that are large and dense, but weak and brittle. The bone is prone to fractures, bowing, and deformities.