Part of “CHAPTER 66 – RARE DISORDERS OF SKELETAL FORMATION AND HOMEOSTASIS“

Fibrous dysplasia, a sporadic unifocal or multifocal developmental skeletal disorder, affects either sex and often causes fractures and deformities.59 The pathogenetic abnormality is an expanding fibrous lesion of bone-forming mesenchyme.4 Monostotic disease typically presents during the second or third decade of life; polyostotic disease manifests before 10 years of age.60 Long bones or the skull are usually affected. Before adolescence, expansile skeletal lesions may fracture, cause deformity, and sometimes entrap nerves. Affected bones occasionally become sarcomatous (incidence of <1%), especially with involvement of the facial bones or the femur.61 Pregnancy may reactivate previously quiescent lesions. Some patients have characteristic hyperpigmented skin macules called café-au-lait spots (Fig. 66-10) and endocrine hyperfunction (i.e., McCune-Albright syndrome).59 The endocrinopathy is usually pseudoprecocious puberty in girls and less commonly thyrotoxicosis, Cushing syndrome, acromegaly, hyperprolactinemia, or hyperparathyroidism.62 Rarely, patients with McCune-Albright syndrome also have renal phosphate wasting and hypophosphatemic bone disease that may represent a form of “oncogenic” rickets or osteomalacia63 (see Chap. 63, Chap. 67, Chap. 70 and chap. 219).