Head & Face Medicine

Download (0)

Full text

(1)

Open Access

Review

The nature of fibrous dysplasia

Liviu Feller*

1

, Neil H Wood

1

, Razia AG Khammissa

1

, Johan Lemmer

1

and Erich J Raubenheimer

2

Address: 1Department of Periodontology and Oral Medicine, School of Dentistry, Faculty of Health Sciences, University of Limpopo (Medunsa Campus), Pretoria, South Africa and 2Department of Oral Pathology, School of Dentistry, Faculty of Health Sciences, University of Limpopo (Medunsa Campus), Pretoria, South Africa

Email: Liviu Feller* - lfeller@ul.ac.za; Neil H Wood - oralmed@ul.ac.za; Razia AG Khammissa - rkhammissa@webmail.co.za;

Johan Lemmer - jbowman@iburst.co.za; Erich J Raubenheimer - Erich.Raubenheimer@ul.ac.za

* Corresponding author

Abstract

Fibrous dysplasia has been regarded as a developmental skeletal disorder characterized by replacement of normal bone with benign cellular fibrous connective tissue. It has now become evident that fibrous dysplasia is a genetic disease caused by somatic activating mutation of the Gsα subunit of G protein-coupled receptor resulting in upregulation of cAMP. This leads to defects in differentiation of osteoblasts with subsequent production of abnormal bone in an abundant fibrous stroma. In addition there is an increased production of IL-6 by mutated stromal fibrous dysplastic cells that induce osteoclastic bone resorption.

Introduction

Fibrous dysplasia (FD) is a sporadic benign skeletal disor- der that can affect one bone (monostotic form), or multi- ple bones (polyostotic form), and the latter may form part of the McCune-Albright syndrome (MAS) or of the Jaffe- Lichtenstein syndrome (JLS). JLS is characterized by poly- ostotic FD and café-au-lait pigmented skin lesions, while MAS has the additional features of hyperfunctional endo- crinopathies manifesting as precocious puberty, hyperthy- roidism or acromegaly [1,2].

Gender prevalence of FD is equal. The monostotic form is more common and affects the 20 to 30 years age group:

polyostotic FD has its onset mainly in children younger than 10 years of age, the lesions grow with the child, sta- bilize after puberty, and most commonly involve cranio- facial bones, ribs, and metaphysis or diaphysis of the proximal femur or tibia [3]. The ratio of occurrence of polyostotic to monostotic FD is 3:7 [4,5].

Signs and symptoms of FD include bone pain, pathologi- cal fractures and bone deformities [6]. Serum alkaline phosphatase (ALP) is occasionally elevated, but calcium, parathyroid hormone, 25-hydroxyvitamin D, and 1,25- dihydroxyvitamin D levels in most cases of FD are nor- mal. Persons with extensive polyostotic FD may have hypophosphatemia, hyperphosphaturia and osteomala- cia [3]. Malignant transformation is rare, and is usually precipitated by radiation therapy [7].

The craniofacial bones are affected in about 10% of cases of monostotic FD and in 50% to 100% of cases of polyos- totic FD [4,8,9]. When only the cranial and facial bones are affected by FD the term craniofacial FD is used. The prevalence of the polyostotic craniofacial FD ranges from 71% to 91% and of the monostotic form, from 10% to 29% [8,9]. FD of the jaws affects the maxilla more fre- quently than the mandible and affects females more fre- quently than males [7].

Published: 9 November 2009

Head & Face Medicine 2009, 5:22 doi:10.1186/1746-160X-5-22

Received: 8 May 2009 Accepted: 9 November 2009

This article is available from: http://www.head-face-med.com/content/5/1/22

© 2009 Feller et al; licensee BioMed Central Ltd.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

(2)

Any cranial or facial bone can be affected by FD and the clinical associated features will depend upon the bone or bones affected. Signs and symptoms can include facial pain, headache, cranial asymmetry, facial deformity, tooth displacement, and visual or auditory impairment (figures 1 and 2) [4,8].

The aetiology of FD

FD is a genetic non-inherited condition caused by mis- sense mutation in the gene GNAS1 on chromosome 20, that encodes the alpha subunit of the stimulatory G pro- tein-coupled receptor, Gsα. The activating mutations occur post-zygotically, replacing the arginine residue amino acid with either a cystein or a histidine amino acid.

The mutation selectively inhibits GTPase activity, result- ing in constitutive stimulation of AMP-protein kinase A intracellular signal transduction pathways [2,6,10-16].

The systemic manifestations of the mutated Gsα protein- coupled receptor complex include autonomous function in bone through parathyroid hormone receptor; in skin through melanocyte-stimulating hormone receptor; in ovaries through the follicle-stimulating hormone recep- tor; and in the thyroid and the pituitary gland, through the thyroid and growth hormone receptors respectively [3].

FD is a somatic mosaic disorder with a broad spectrum of phenotypic heterogeneity. The extent of the disease is related to the stage at which the post-zygotic mutation in Gsα had occurred, whether during embryonic develop- ment or postnatally [13,16].

Polyostotic FD can affect bones derived from mesoderm or neural crest, and is associated with pregastrulation

mutation. The same process associated with multiple- organ manifestations of Gsα mutation is referred to as McCune-Albright syndrome. The mutated pluripotential cell develops into a mutated clone of cells affecting bones in the case of FD, and affecting multiple organs together with bones in the case of McCune-Albright syndrome [6].

Monostotic FD and polyostotic FD without either cranio- facial skeletal or extraskeletal organ involvement can develop from a post-gastrulation mutation; but since polyostotic FD nearly always involves craniofacial bones, it is reasonable to assume that the monostotic FD is the only form of FD that can develop post-gastrulation [6].

Severity and extent of Gsα mutation-associated diseases are not related to the stage of embryogenesis when the mutation occurred, but rather are functions of survival of mutated cells within the clone during migration, growth and differentiation, and of the ratio of mutated to normal cells at the affected anatomical site [6,13].

The postnatal manifestation of FD is not a reflection of the stage of development when the mutation occurred but indicates the time that the dynamic equilibrium between mutated and normal osteogenic cells in the mosaic fibrous dysplastic bone favoured the mutated cells. Possi- ble factors influencing the dominance of mutated over normal cells include growth factors and hormones [6], and it is probable that there is a 'critical mass' of mutated cells necessary for the development of FD. The burden of mutated cells in FD frequently declines with age, owing to imponderable suppressive influences shifting the balance of transformed to normal cells towards predominance of normal cells, resulting in arrest of FD [6].

The cellular portion of the abnormal bone in FD is com- posed of a mosaic of mutated and non-mutated osteo- Craniofacial fibrous dysplasia showing a diffuse swelling of the

right maxillary region causing facial asymmetry Figure 1

Craniofacial fibrous dysplasia showing a diffuse swell- ing of the right maxillary region causing facial asym- metry.

Intraoral view of case shown in figure 1 Figure 2

Intraoral view of case shown in figure 1. Note the dif- fuse expansion of the palate and buccal bony plate of the maxilla.

(3)

genic cells [16]. In fibrous dysplastic bone, the increased expression of cAMP by the mutated lesional cells is asso- ciated with abnormal osteoblast differentiation and for- mation of defective bone [17]. Fibrous dysplastic lesions have characteristic changes in bone matrix organization, in expression of certain non-collagenous proteins of the extracellular matrix, and in mineralization; and the mutated cells within the lesion are morphologically altered [15].

The skeletal lesions of FD

Focal lesions of FD are somatic mosaics, and the severity and extent of the bony lesions are a function of the ratio between the mutated cells and the normal osteoblasts;

and of the severity of cytogenic alterations and the subse- quent functional impairment of the mutated cells [3,10].

The cellular component of the bony lesions of FD com- prises mesenchymal cells of osteogenic lineage. There is a variable ratio between normal osteoblasts and mutated fibroblast-like cells. The mutated cells are poorly differen- tiated, functionally impaired osteoblasts with an increased proliferation rate [17], and are capable of pro- ducing extracellular matrix and woven bone. However the woven bone is abnormal in organization and in composi- tion.

The bone matrix in fibrous dysplastic lesions is deficient in osteopontin and in bone sialoprotein (BSP), compared to normal bone. BSP is a marker of osteoblastic cell differ- entiation and its expression is required for mineralization [2,17]. Indeed, fibrous dysplastic bone lesions demon- strate a deficit in mineralization that can be defined as localized osteomalacia. The unmineralized woven bone in long bones at sites where FD develops never matures into lamellar bone; and the local 'normal' mineralized bone adjacent to the lesion shows a relatively low mineral concentration. However, in persons with FD, the bones that are not affected by FD do not have osteomalacic changes [14,15]. In contrast to FD of long bones, in craniofacial FD the immature woven bone may undergo lamellation. These differences between the mineralization of FD of long bones and of craniofacial membranous bones, may be owing to the fact that these two embryolog- ically distinct types of bone are under different inductive influences during development.

In addition to the osteomalacic changes, fibrous dysplas- tic bone shows increased osteoclastic activity, and markers of bone resorption may be elevated in some affected per- sons [15]. The mutated stromal cells of FD express high levels of IL-6 owing to the inherited cellular excess of cAMP. The increased levels of IL-6 stimulate osteoclas- togenesis that contributes to the bone resorption at the site of FD [10]. Thus the fibrous dysplastic bone is charac-

terized by increased bone resorption and poor mineraliza- tion.

FD and bone lesions caused by hyperparathyroidism are similar in nature, and are generated by the intracellular downstream effect of the activation of the parathyroid hormone (PTH) G protein-coupled receptor of osteogenic cells. While in hyperparathyroidism PTH receptor is over stimulated by excess PTH, in FD the same receptor is inherently active owing to the mutation in the α subunit of the G protein [12]. The end result in both FD- and in hyperparathyroidism-associated bony lesions is an increase in osteoclastogenesis resulting in bone resorp- tion. However, while hyperparathyroidism-induced bony lesions are characterized by tunnelling bone resorption [15], there is evidence that fibrous dysplastic lesional cells are more sensitive and responsive to PTH stimulation than normal osteoblasts, but tunnelling resorption is not evident in persons with FD that do not have parathy- roidism [15].

Radiological features and microscopic features of FD

The radiological features of FD are diverse and are dependent upon the proportion of mineralized bone to fibrous tissue in the lesion [17]. Early FD of craniofacial bones is radiolucent with either ill defined or well defined borders, and may be unilocular or multilocular. As the lesions mature, the bony defects acquire a mixed radiolu- cent/radiopaque appearance, and established FD exhibits mottled radiopaque patterns often described as resem- bling ground glass, orange peel or fingerprints, with ill defined borders blending into the normal adjacent bone (figure 3) [1,9,18].

Cropped panoramic radiograph of fibrous dysplasia of the left mandible

Figure 3

Cropped panoramic radiograph of fibrous dysplasia of the left mandible. Note the diffuse mottled-glass appearance and tooth displacement.

(4)

Microscopically, FD comprises irregular trabeculae of woven bone, blending into the surrounding normal bone (figure 4) and lying within a cellular fibrous stroma with osteoblast progenitor cells resembling fibroblasts (figure 5) [19]. These trabeculae of woven bone have been fanci- fully said to resemble Chinese script writing [1].

Early craniofacial FD is characterized by minimally miner- alized deposits of woven bone with a continuum progres- sive lamellation of the woven bone trabeculae as FD becomes more mature (figure 6). This is in contrast to FD lesions in long bones where mature lamellar bone is not found [15].

Treatment of FD

There is no cure for FD, and the existing guidelines for treatment are not universally accepted. Spontaneous reso- lution of FD does not occur [17]. Fibrous dysplastic lesions that are not symptomatic, that do not progress and that do not cause deformities or functional impairment should simply be monitored [8]. Surgical intervention is required when important structures are in danger of com- pression [9]. However, after surgical reduction of fibrous dysplastic lesions, particularly in younger subjects and when the lesions are more immature, is high (50%) [8,9], so a conservative surgical approach will often require more than one intervention to control the clinical signs and symptoms [8]. As an alternative treatment, when sur- gery is not indicated, relief of bone pain and reduction of osteoclastic activity with partial filling of osteolytic lesions can be achieved with intravenous bisphosphonate ther- apy [3,17,20].

Conclusion

Fibrous dysplastic lesional cells are committed osteogenic precursor cells with impaired capacity to differentiate into normal functioning osteoblasts. The defects in osteoblast differentiation are associated with Gsα mutation of both neural crest and mesoderm-derived osteogenic cells and may thus affect any part of the osteogenic compartment.

Poorly demarcated line of fusion between FD bone (left of arrow) and residual bone (right of arrow) (H&E stain, ×100) Figure 4

Poorly demarcated line of fusion between FD bone (left of arrow) and residual bone (right of arrow) (H&E stain, ×100).

Fibroblast-like osteoblast progenitor cells forming a woven bone deposit in a fibrous matrix

Figure 5

Fibroblast-like osteoblast progenitor cells forming a woven bone deposit in a fibrous matrix. Note the absence of osteoblastic rimming around the woven bone (H&E stain, ×250).

Polarized light photomicrograph of craniofacial FD showing lamellation of Chinese character-like trabeculae (H&E stain, polarized light, ×150)

Figure 6

Polarized light photomicrograph of craniofacial FD showing lamellation of Chinese character-like trabec- ulae (H&E stain, polarized light, ×150).

(5)

Publish with BioMed Central and every scientist can read your work free of charge

"BioMed Central will be the most significant development for disseminating the results of biomedical researc h in our lifetime."

Sir Paul Nurse, Cancer Research UK

Your research papers will be:

available free of charge to the entire biomedical community peer reviewed and published immediately upon acceptance cited in PubMed and archived on PubMed Central yours — you keep the copyright

Submit your manuscript here:

http://www.biomedcentral.com/info/publishing_adv.asp

BioMedcentral

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

NHW, RAGK contributed to the literature review. LF, JL, NHW and EJR contributed to the conception of the article.

LF, JL, NHW and RAG contributed to the manuscript prep- aration. EJR carried out histological analyses and drafted the histology section. Each author reviewed the paper for content and contributed to the manuscript. All authors read and approved the final manuscript.

References

1. Neville BW, Damm DD, Allan CM, Bouquot JE: Bone Pathology. In Oral and Maxillofacial Pathology 2nd edition. WB Saunders Company;

2002:635-640.

2. Abdel-Wanis ME, Tsuchiya H: Melatonin deficiency and fibrous dysplasia: might a relation exist? Med Hypotheses 2002, 59:552-554.

3. Faves MJ, Vokes TJ: Paget disease and other dysplasias of bone.

In Harrison's principles of Internal Medicine 16th edition. Edited by:

Kasper DL, Braunwald E, Fauci AS, Hauser SL, Longo DL, Jameson JL.

New York, McGraw-Hill; 2005:2279-2286.

4. Alam Wg, Cdr A, Chander Gp, Capt BN: Craniofacial fibrous dys- plasia presenting with visual impairment. MJAFI 2003, 59:342-343.

5. Yetiser S, Gonul E, Tosun F, Tasar M, Hidir Y: Monostotic cranio- facial fibrous dysplasia: The Turkish experience. J Craniofac 2006, 171:62-67.

6. Riminucci M, Saggio I, Robey PG, Bianco P: Fibrous dysplasia as a stem cell disease. J Bone and Mineral Res 2006, 21:P125-P131.

7. Ogunsalu CO, Lewis A, Doonquah L: Benign fibro-osseous lesions of the jaw bones in Jamaica: analysis of 32 cases. Oral Dis 2001, 7:155-162.

8. Lustig LR, Holliday MJ, McCarthy EF, Nager GT: Fibrous dysplasia involving the skull base and temporal bone. Arch Otolaryngol Head Neck Surg 2001, 127:1239-1247.

9. Panda NK, Parida PK, Sharma R, Jain A, Bapuraj JR: A clinicoradio- logic analysis of symptomatic craniofacial fibro-osseous lesions. Otolaryngol Head Neck Surg 2007, 136:928-933.

10. Riminucci M, Kuznetsov SA, Cherman N, Corsi A, Bianco P, Gehron Robey P: Osteoclastogenesis in fibrous dysplasia of bone: in situ and in vitro analysis of IL-6 expression. Bone 2003, 33:434-442.

11. Bianco P, Kuznetsov SA, Riminucci M, Fisher LW, Spiegel AM, Gehron Robey P: Reproduction of human fibrous dysplasia of bone in immunocompromized mice by transplanted mosaics of nor- mal and Gsα-mutated skeletal progenitor cells. J Clin Investig 1998, 101:1737-1744.

12. Bianco P, Robey PG: Diseases of bone and stromal cell lineage.

J Bone and Mineral Res 1999, 14:336-341.

13. Cohen MM, Howell RE: Etiology of fibrous dysplasia and McCune-Albright syndrome. Int J Maxillofac Surg 1999, 28:366-371.

14. Terpstra L, Rauch F, Plotkin H, Travers R, Glorieux FH: Bone min- eralization in polyostotic fibrous dysplasia: histomorpho- metric analysis. J Bone Miner Res 2002, 17:1949-1953.

15. Corsi A, Collins MT, Riminucci M, Howell PG, Boyde A, Robey PG, Bianco P: Osteomalacic and hyperparathyroid changes in fibrous dysplasia of bone: biopsy studies and clinical correla- tions. J Bone Miner Res 2003, 18:1235-1246.

16. Leet AI, Chebli C, Kushner H, Chen CC, Kelly MH, Brillante BA, Robey PG, Bianco P, Wientroub S, Collind MT: Fracture incidence in polyostotic fibrous dysplasia and the McCune-Albright syndrome. J Bone Miner Res 2004, 19:571-577.

17. Charpurlat RD, Meunier PJ: Fibrous dysplasia of bone. Bailliere's Clin Rheumatol 2000, 14:385-398.

18. Grasso DL, Guerci VI, Di Emidio P, De Vescovi R, Ukmar M, Catta- ruzzi E, Zocconi E: Dizziness as presenting symptom of monos- totic fibrous dysplasia. Int J Pediatr Otorhinolaryngol Extra 2006, 1:138-141.

19. Sakamoto A, Oda Y, Iwamoto Y, Tsuneyoshi M: A comparative study of fibrous dysplasia and osteofibrous dysplasia with regard to Gsalpha mutation at the Arg201 codon: polymer- ase chain reaction-restriction fragment length polymor- phism analysis of paraffin-embedded tissues. J Mol Diagn 2000, 2:67-72.

20. Chapurlat R: Medical therapy in adults with fibrous dysplasia of bone. J Bone Miner Res 2007, 21:P114-P117.

Figure

Updating...

References

Related subjects :