Fibrous dysplasia

Current approach to fibrous dysplasia of bone and McCune-Albright syndrome

Fibrous dysplasia (FD) of bone is an uncommon disease caused by sporadic, congenital mutations in the cAMP regulating protein, G(s)alpha. It is an example of somatic mosaicism in which a wide spectrum of disease is possible. Widespread skeletal involvement is often associated with varying combinations of café-au-lait skin spots, and/or endocrine dysfunction (precocious puberty, renal phosphate wasting, hyperthyroidism, and/or growth hormone excess). Unrecognized and untreated endocrine dysfunction can exacerbate the skeletal disease. The diagnosis is usually established on clinical grounds on the basis of physical examination and typical radiographic appearance. Occasionally, gene testing of affected tissue may be helpful. The skeletal sites involved with disease are established at an early age, and the complications of fracture deformity are most pronounced in childhood. Bone pain in the absence of a fracture is more common in adults, but can also be present in children. Treatment with bisphosphonates is usually effective at relieving pain, but probably has no effect on the natural history of the disease. Scoliosis, which was previously thought to be an uncommon occurrence, has been shown to be common and progressive, and as such, warrants investigation and, when necessary, surgical treatment. The surgical management of FD remains challenging. Timing and technique remain controversial, but some consensus exists in that grafting materials (of any type) usually fail and should not be a central aspect of the surgical approach. Intramedullary devices are in general superior to side plates and screws. In extremely widespread disease with very early fracture and deformity, no surgical approach will affect final functional outcome. Efforts should be made for the initiation of international collaborative studies to better define optimal surgical approaches to the treatment of this challenging disease.

Physical function is impaired but quality of life preserved in patients with fibrous dysplasia of bone

Fibrous dysplasia of bone (FD) is a congenital, non-heritable skeletal disorder that is associated with multiple skeletal complications, including repeated fractures, limb length discrepancy, and bone pain. The disease-specific impact of FD on quality of life outcomes is unknown. We sought to understand the impact of the scope and extent of the skeletal disease on quality of life in adults and children with FD. The health-related quality of life was quantified in a population of adults (n = 56) and children (n = 22) with FD using validated health assessment questionnaires, the Medical Outcomes Study 36 Item Short-Form Health Survey, volume 2 (SF36) (adults) and the Child Health Questionnaire Parent Form 50 (CHQ-PF50) (children). Clinical demographic data and skeletal disease burden scores (SDBS, amount of skeleton involved with FD) were measured, and correlations with health-related quality of life were sought. The SF36 and CHQ-PF50 revealed lower Physical Function Summary scores in FD patients compared to the U.S. population norms (adult 41 vs. 50, Z score < -5.0, pediatric 39 vs. 50, Z score < -5.0). However, the SF36 and CHQ-PF50 Mental/Psychological summary scores were not different from those of U.S. population norms (adult 50 vs. 50, Z score = 0, pediatric 48 vs. 50 Z score = -0.9). The score on the Physical Function Domain of both tools was strongly negatively associated with the SDBS (adult Spearman rho = -0.43, P = 0.009, pediatric Spearman rho = -0.72, P = 0.005). The groups of adult and pediatric patients with SDBS > 30 had decreased Physical Function Domain scores when compared to those with scores < 30 (adult 35 vs. 45, P = 0.002, pediatric 57 vs. 78, P = 0.04, respectively). One of the largest effects was seen in the parents of children with FD, who had significantly lower Parental Emotional scores than those of the parents of healthy norms (54 vs. 88, Z score < -5.0), suggesting a high degree of emotional morbidity in the parents of children with FD. Despite measurable functional limitations in adults and children, and significant parental emotional impairment, patients with FD achieve a high level of social and emotional function. These data are important for prognosis and parental reassurance.

Glucocorticoids decrease interleukin-6 levels and induce mineralization of cultured osteogenic cells from children with fibrous dysplasia

Fibrous dysplasia (FD) is a progressive bone disease in which abnormal fibroblast proliferation results in the replacement of normal cancellous bone with an immature fibrous tissue that is poorly mineralized. The disease manifests itself in the monostotic form in which only one bone is involved and the polyostotic form in which multiple bones at different sites are affected. The McCune-Albright syndrome is a variation of the polyostotic form in which patients demonstrate a greater extent of bone involvement and a variety of endocrinopathies. Somatic activating mutations in the GNAS gene have been demonstrated in the fibrotic lesions of patients affected with either monostotic or polyostotic FD. The increased cAMP levels caused by the G-protein mutations lead to increased interleukin-6 (IL-6) levels in the affected tissues, resulting in abnormal osteoblast differentiation and increased osteoclastic activity. Utilizing cell culture techniques that have been developed for mammalian bone marrow stromal cells, we have successfully cultured osteogenic stem cells from the affected stroma of 11 FD patients. Cells cultured from patients with polyostotic FD showed a high frequency of the Gsalpha mutation, whereas cells from monostotic FD patients showed a low frequency of the mutation. Both the normal and FD cells displayed the osteogenic phenotype when exposed to medium containing glucocorticoids. Glucocorticoids also caused a dramatic inhibition of IL-6 mRNA and protein levels in osteogenic cells cultured from the FD patients. These findings suggest that chemical alteration of cellular function may lead to new treatment options for patients with FD.