Fibrous dysplasia is a benign* bone condition in which abnormal fibrous tissue develops in place of normal bone. As these areas of fibrous tissue grow and expand over time, they can weaken the bone — causing it to fracture or become deformed.
Some patients with fibrous dysplasia experience few or no symptoms. In other cases, however, multiple bones are affected and the condition is more severe. These patients may need surgery to remove the affected areas of bone and prevent or repair any fractures or deformity.
Fibrous dysplasia is rare, accounting for just about 7% of all benign bone tumors. It can affect any bone in the body, but most often occurs in the:
Fibrous dysplasia has been linked to a gene mutation that causes bone cells to make an abnormal type of fibrous bone. Although the abnormal bone begins to form before birth, its presence is often not discovered until childhood, adolescence or even adulthood.
The condition is generally divided into two types:
Fibrous dysplasia is a chronic disorder and is often progressive. Although the lesions may stabilize and stop growing, they do not disappear. Individual lesions may progress more rapidly in the polyostotic form of the condition and in growing children.
In patients with fibrous dysplasia, the same abnormality that occurs in the bone cells can also occur in the body's gland cells, leading to hormonal abnormalities. Although this is rare, it can occur in severe forms of polyostotic fibrous dysplasia.
Fibrous dysplasia may occur as part of a larger disorder. For example, McCune-Albright syndrome is characterized by polyostotic fibrous dysplasia that occurs with hormonal abnormalities and areas of darkened skin ("café au lait" spots).
*It is very rare for areas of fibrous dysplasia to become malignant or cancerous. This occurs in less than 1% of patients and is more likely to happen in patients with the polyostotic form of the condition or in patients with McCune-Albright syndrome.
The cause of the gene mutation is unknown. It is not inherited and is not known to be caused by diet or environmental factors. The mutation occurs equally in males and females of all races.
In some cases, lesions are painless and do not cause symptoms. When this happens, the condition may be found unexpectedly when X-rays or tests are performed for an unrelated injury or medical condition. When symptoms do occur, they reflect the size and severity of the lesion.
As fibrous bone tissue grows and expands, the affected area can become weak and painful. Pain is more likely to occur if the bone affected is one of the weight-bearing bones of the leg or pelvis. Pain caused by fibrous dysplasia generally begins as a dull ache that worsens with activity and lessens with rest. It can get progressively worse over time.
Fibrous bone is very weak when compared to normal bone. It can sometimes break or fracture through the weakened area causing sudden and severe pain. A fracture often occurs after a period of dull pain — although it may also happen suddenly with no prior pain at all.
From the American academy of Orthopaedic Surgeons
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