Fibrous Dysplasia of Bone - Pathophysiology

Pathophysiology

In fibrous dysplasia, the medullary cavity of bones is filled with fibrous tissue, causing the expansion of the areas of bone involved.. The bony trabeculae are abnormally thin and irregular, and often likened to Chinese characters.

The cause of this transformation, in turn, is not completely known, however. Levels of the transcription factor C-fos are raised in fibrous dysplasia, leading to gene over-expression and tumour formation. It is not hereditary. There are two types of fibrous dysplasia:

1. Monostotic (Involving a single bone, or adjacent bones, like both the upper and lower jaw)
2. Polyostotic (Involving many bones).

The most severe form of polyostotic fibrous dysplasia is known as McCune-Albright syndrome. Fibrous dysplasia of bone may also be an associated abnormality in Neurofibromatosis type II.