Fibrous dysplasia
Fibrous dysplasia of bone (FD) (OMIM #174800) is an uncommon skeletal disorder with a broad spectrum of clinical presentation. On one end of the spectrum, patients may present in adulthood with an incidentally discovered, asymptomatic radiographic finding of no clinical significance. On the other end of the spectrum, patients present early in life with disabling disease. The disease may involve one bone (monostotic FD), multiple bones (polyostotic FD), or the entire skeleton (panostotic FD) [1–3]. FD may be associated with a wide range of extraskeletal manifestations, the most common of which is patches of cutaneous hyperpigmentation commonly referred to as café?au?lait macules. These lesions vary widely in size but typically have characteristic features that include jagged, “coast of Maine” borders, some relationship with the midline, and sometimes follow the developmental lines of Blashcko (Fig. 108.1A–E). Other extraskeletal manifestations include hyperfunctioning endocrinopathies, such as precocious puberty, hyperthyroidism, growth hormone excess, and Cushing’s syndrome. FD in combination with one or more extraskeletal manifestations is known as McCune–Albright syndrome (MAS) [4–7]. Renal phosphate wasting caused by overproduction of FGF23 by dysplastic bone cells, is one of the more common and clinically significant extraskeletal manifestations [8]. An association of FD with possibly premalignant, cystic lesions of the pancreas (intraductal papillary mucinous neoplasms) has recently been reported, and is emerging as one of the more common extraskeletal manifestations [9]. More rarely, FD may be associated with intramuscular myxomas (Mazabraud’s syndrome) [10] or dysfunction of the heart, liver, or other organs within the context of the MAS [11].