Fibrous Dysplasia of Bone and McCune-Albright Syndrome: A Bench to Bedside Review

A Mathematical Model for Fibrous Dysplasia: The Role of the Flow of Mutant Cells

Fibrous dysplasia (FD) is a mosaic non-inheritable genetic disorder of the skeleton in which normal bone is replaced by structurally unsound fibro-osseous tissue. There is no curative treatment for FD, partly because its pathophysiology is not yet fully known. We present a simple mathematical model of the disease incorporating its basic known biology, to gain insight on the dynamics of the involved bone-cell populations, and shed light on its pathophysiology. We develop an analytical study of the model and study its basic properties. The existence and stability of steady states are studied, an analysis of sensitivity on the model parameters is done, and different numerical simulations provide findings in agreement with the analytical results. We discuss the model dynamics match with known facts on the disease, and how some open questions could be addressed using the model.

Mazabraud's syndrome in female patients: Two case reports

BACKGROUND

Mazabraud's syndrome (MS) is a rare and slowly progressive benign disease characterized by the concurrent presence of fibrous dysplasia of bone and intramuscular myxoma, and is thought to be associated with mutations of the GNAS gene. To date, only about 100 cases of MS have been reported in the literature, but its standard treatment strategy remains unclear.

CASE SUMMARY

We report two cases of MS in young women who underwent different treatments based on their symptoms and disease manifestations. The first patient, aged 37, received internal fixation and intravenous bisphosphonate for a pathological fracture of the right femoral neck, excision of a right vastus medialis myxoma was subsequently performed for pain control, and asymptomatic psoas myxomas were monitored without surgery. Genetic testing confirmed a GNAS gene mutation in this patient. The second patient, aged 24, underwent right vastus intermedius muscle myxoma resection, and conservative treatment for fibrous dysplasia of the ilium. These patients were followed-up for 17 months and 3 years, respectively, and are now in a stable condition.

CONCLUSION

Various treatments have been selected for MS patients who suffer different symptoms. The main treatment for myxomas is surgical resection, while fibrous dysplasia is selectively treated if the patient experiences pathological fracture or severe pain. However, given the documented instances of malignant transformation of fibrous dysplasia in individuals with MS, close follow-up is necessary.

Radiographic Orofacial Findings of Systemic Diseases

This article discusses the orofacial clinicoradiographic features of systemic diseases that manifest in the orofacial region. The systemic diseases discussed are grouped into the following: autoimmune diseases, endocrine diseases, bone diseases, hematologic diseases, syndromes, and malignancies. The radiographic manifestation ranges from radiolucent bony destruction, increased bone density, calcification, thinning of cortical plate, loss of trabeculation, missing teeth, and supernumerary teeth. It is imperative for clinicians to be cognizant of these findings, as they may be the first manifestation of these systemic diseases.

Coexistence of meningioma and craniofacial fibrous dysplasia: a case series of clinicopathological study and literature review

BACKGROUND

The co-existence of meningioma and craniofacial fibrous dysplasia (CFD) is rare. Due to the similar radiological characteristics, it is challenging to differentiate such co-existence from solitary hyperostotic meningioma resulting in a dilemma of prompt diagnosis and appropriate intervention.

METHOD

We conducted a retrospective review of the data from 21 patients with concomitant meningioma and CFD who were treated at Beijing Tiantan Hospital from 2003 to 2021. We summarized their clinicopathological features and performed a comprehensive literature review. Additionally, we tested the characteristic pathogenic variants in exon 8 and 9 of GNAS gene and the expression of corresponding α-subunit of the stimulatory G protein (Gαs) related to CFD to explore the potential interactions between these two diseases.

RESULTS

The cohort comprised 4 men and 17 women (mean age, 45.14 years). CFD most commonly involved the sphenoid bone (n = 10) and meningiomas were predominantly located at the skull base (n = 12). Surgical treatment was performed in 4 CFD lesions and 14 meningiomas. Simpson grade I-II resection was achieved in 12 out of the 14 resected meningiomas and almost all of them were classified as WHO I grade (n = 13). The mean follow-up duration was 56.89 months and recurrence was noticed in 2 cases. Genetic study was conducted in 7 tumor specimens and immunohistochemistry was accomplished in 8 samples showing that though GNAS variant was not detected, Gαs protein were positively expressed in different degrees.

CONCLUSIONS

We presented an uncommon case series of co-diagnosed meningioma and CFD and provided a detailed description of its clinicopathological features, treatment strategy and prognosis. Although a definite causative relationship had not been established, possible genetic or environmental interplay between these two diseases could not be excluded. It was challenging to initiate prompt diagnosis and appropriate treatment for concomitant meningioma and CFD because of its similar radiological manifestations to meningioma with reactive hyperostosis. Personalized and multi-disciplinary management strategies should be adopted for the co-existence of meningioma and CFD.

Craniofacial Fibrous Dysplasia in Fronto-Orbital Region: A Single-Center Retrospective Study of 38 Cases

OBJECTIVE

This study presents the clinical characteristics, imaging manifestations, and surgical experience in 38 patients diagnosed with craniofacial fibrous dysplasia in fronto-orbital region (foFD).

METHODS

We retrospectively analyzed the clinical data from 38 patients who had surgery for foFD. The surgical procedure typically involved extensive tumor removal, followed by immediate reconstruction of the frontal bone and orbit using synthetic materials. Additionally, 9 patients underwent simultaneous microscopic decompression of the optic canal.

RESULTS

Common clinical manifestations included progressive fronto-orbital bone deformity (35), proptosis (28), orbital dystopia (21), and visual impairment (9). The disease primarily affecting the frontal bone (38), the sphenoid bone (28), and the ethmoid bone (24). The optic canal was involved in 9 patients with functional impairment. Computed tomography scans in all 38 cases revealed satisfactory repair material positioning and complete resolution of frontal deformities. Among the 9 patients who underwent optic canal decompression, 7 experienced partial recovery of visual acuity after surgery.

CONCLUSIONS

In the surgical treatment of foFD, it is crucial to achieve maximal bone resection and repair skull defects, while decompressing the optic canal can provide significant benefits for patients with decreased visual function preoperatively. The use of preformed artificial materials offers advantages in aesthetic restoration after lesion excision.

Periosteal Fasciitis With Unusual Radiologic Features Harboring a Novel STAG1::USP6 Fusion Gene

Periosteal fasciitis is a subtype of nodular fasciitis originating from the periosteum. The diagnosis can be challenging and requires radiologic-pathologic correlation. Advances in molecular analysis confirmed that nodular fasciitis and its related lesions harbor a USP6 gene rearrangement with one of the several potential partners. Herein, we report a case of periosteal fasciitis with metaplastic bone formation detected incidentally during a radiologic survey for breast carcinoma. Radiologic examination revealed a 2.4 cm, heterogeneous, avidly enhancing lesion of the right femoral distal metaphysis concerning for low-grade periosteal chondrosarcoma. Histological examination of a core needle biopsy revealed a tumor composed of bland spindle cells with myofibroblastic and osteoblastic phenotypes admixed with immature bone and cartilaginous elements. Molecular analysis revealed a novel STAG1::USP6 fusion that helped arrive at the right diagnosis and further expands the molecular profile of USP6-associated neoplasms.

Denosumab use in bone fibrous dysplasia refractory to bisphosphonate: A retrospective multicentric study

INTRODUCTION

Increased RANKL expression is observed in the bone tissue of fibrous dysplasia of bone/McCune-Albright syndrome (FD/MAS). In one animal model of FD/MAS, the inhibition of RANKL reduced tumor volume. A beneficial effect of denosumab on pain in patients refractory to bisphosphonates has been reported, but without systematic quantification of pain improvement. This work describes the clinical experience of our group on the efficacy on pain of denosumab treatment, along with safety, in FD/MAS patients refractory to bisphosphonates.

MATERIALS AND METHODS

We have conducted a retrospective multicenter study in 6 academic rheumatology centers in France. We have collected patients and FD/MAS characteristics, duration of prior exposure to bisphosphonates, denosumab treatment modalities (dosage - administration regimen - number of courses); evolution of pain evaluated by Visual Analogic Scale (VAS).

RESULTS

13 patients were included (10 women and 3 men) 45 years on average, 5 MAS, 4 monostotic and 4 polyostotic forms. The average duration post-diagnosis of FD/MAS was 25 years and the mean duration of prior exposure to bisphosphonates was 4.7 years. Pain could be analyzed in 7 patients, showing a significant improvement from a mean VAS of 7.8 to 2.9 (-4.9 points, p = 0.003). In one patient with fronto-orbital FD/MAS, a 30 % decrease in lesional volume, assessed by MRI, was observed within 6 months of treatment, that was sustained over the following 12 months. Treatment regimens were heterogeneous. No hypercalcemia was observed after treatment cessation and the clinical tolerance was good.

DISCUSSION

This study suggests that denosumab reduces pain in patients with DF/MAS refractory to bisphosphonates, and quantifies this improvement for the first time in a multicenter study. In our cohort, no patients who discontinued denosumab developed hypercalcemia and clinical tolerance was overall good. This study also provides encouraging data regarding lesion volume control. Further controlled studies are required to determine the place and modalities of the denosumab treatment of FD/MAS.

CONCLUSION

Denosumab significantly decreased pain in FD/MAS refractory to bisphosphonate. This study paves the way for a randomized clinical trial to validate and standardize the prescription of denosumab in FD/MAS.

McCune-Albright Syndrome: A Case Report and Review of Literature

McCune-Albright syndrome (MAS) is a rare sporadic condition defined by the classic triad of fibrous dysplasia of bone, café au lait skin macules, and hyperfunctioning endocrinopathies. The molecular basis of MAS has been ascribed to the post-zygotic somatic gain-of-function mutations in the GNAS gene, which encodes the alpha subunit of G proteins, leading to constitutive activation of several G Protein-Coupled Receptors (GPCRs). The co-occurrence of two of the above-mentioned cardinal clinical manifestations sets the diagnosis at the clinical level. In this case report, we describe a 27-month-old girl who presented with gonadotropin-independent precocious puberty secondary to an estrogen-secreting ovarian cyst, a café au lait skin macule and growth hormone, and prolactin excess, and we provide an updated review of the scientific literature on the clinical features, diagnostic work-up, and therapeutic management of MAS.

Current concepts of craniofacial fibrous dysplasia: pathophysiology and treatment

Fibrous dysplasia is an uncommon genetic disorder in which bone is replaced by immature bone and fibrous tissue, manifesting as slowgrowing lesions. Sporadic post-zygotic activating mutations in GNAS gene result in dysregulated GαS-protein signaling and elevation of cyclic adenosine monophosphate in affected tissues. This condition has a broad clinical spectrum, ranging from insignificant solitary lesions to severe disease. The craniofacial area is the most common site of fibrous dysplasia, and nine out of 10 patients with fibrous dysplasia affecting the craniofacial bones present before the age of 5. Surgery is the mainstay of treatment, but the technique varies according to the location and severity of the lesion and associated symptoms. The timing and indications of surgery should be carefully chosen with multidisciplinary consultations and a patient-specific approach.

Hyperthyroidism in McCune-Albright Syndrome - a case report

OBJECTIVES

We intend to describe a case of McCune-Albright Syndrome (MAS), a rare disease characterized by fibrous dysplasia (FD), cutaneous hyperpigmentation and hyperfunctioning endocrinopathies (HFE).

CASE PRESENTATION

We report the case of a 13-year-old male child who presented with a café-au-lait macule in the lumbosacral region and disabling polyostotic FD, requiring several surgical interventions and bisphosphonates from the age of 3 years (Y) + 9 months (M) due to persistent and severe pain. Hyperthyroidism (HT) became apparent at 5 Y + 1 M with a T3/T4 ratio greater than 20. Treatment with anti-thyroid drugs (ATD) was carried out for 7 Y and there was a progressive improvement in pain complaints 8 M after starting ATD, allowing treatment with pamidronate to be discontinued. Total thyroidectomy was performed at 12 Y + 5 M.

CONCLUSIONS

This is a case of MAS-associated HT that reflects the deleterious effect of thyroid hormone excess on FD, reinforcing the need of having a low threshold for suspicion of HFE that may arise.

One half-century of advances in the evaluation and management of disorders of bone and mineral metabolism in children and adolescents

The past 50 years of research in pediatric bone and mineral metabolism have led to remarkable progress in the identification and characterization of disorders that affect the developing skeleton. Progress has been facilitated through advances in both technology and biology and this paper provides a brief description of some but not all of the key findings, including identification of the calcium sensing receptor and the polypeptides parathyroid hormone and parathyroid hormone-related protein as well as their shared receptor and signal generating pathways; the elucidation of vitamin D metabolism and actions; discovery of fibroblast growth factor 23 (FGF23), the sodium-phosphate co-transporters and the other components that regulate phosphate metabolism. Moreover, the past half-century of research has led to the delineation of the molecular bases for genetic forms of hypoparathyroidism, pseudohypoparathyroidism, and primary hyperparathyroidism as well as the determination of the genetic causes of osteogenesis imperfecta, osteopetrosis, hypophosphatasia, and other disorders of mineral/bone homeostasis. During the next decade we expect that many of these fundamental discoveries will lead to the development of innovative treatments that will improve the lives of children with these disorders.

Hyperfunctioning parathyroid gland and skeletal involvement on [18F]fluorocholine PET/CT: one look with two views

Hyperparathyroidism is an endocrine disorder that may be associated with other metabolic diseases. Non-invasive imaging techniques including [^99mTc]Tc-sestamibi single-photon emission computed tomography (SPECT) and [¹⁸F]fluorocholine positron emission tomography (PET)/computed tomography (CT) play a key role on management of patients with hyperparathyroidism. We report for the first time a case of a patient with evidence of both hyperfunctioning parathyroid tissue and multiple lytic bone lesions on [¹⁸F]fluorocholine PET/CT imaging. The present case report highlights the potential role of whole-body [¹⁸F]fluorocholine PET/CT for the identification of both parathyroid adenoma and multiple bone lesions in a single diagnostic setting.

Risk factors for fracture in patients with fibrous dysplasia of the proximal femur

OBJECTIVE

The primary aim of this retrospective observational clinical study was to explore the risk factors for fracture in patients with fibrous dysplasia (FD) of the proximal femur.

METHODS

We investigated body mass index, bilateral radiographs on both sides, femoral neck shaft angle measurements, and markers of bone metabolism in patients with FD of the proximal femur according to whether or not they had sustained a hip fracture. Nine clinical parameters (age, sex, clinical classification, anatomic classification, femoral neck shaft angle, and procollagen type 1 N-terminal propeptide, C-terminal telopeptide of type I collagen, and osteocalcin levels) were selected for univariate analysis. Factors that were significant in univariate analysis were then subjected to multivariate logistic analysis.

RESULTS

Clinical classification, anatomic classification, femoral neck shaft angle, and the osteocalcin level were identified to be statistically significant risk factors for fracture in univariate analysis. Anatomic classification, femoral neck shaft angle, and the osteocalcin level remained significant risk factors in multivariate analysis.

CONCLUSIONS

Anatomic classification, femoral neck shaft angle, and the osteocalcin level are important risk factors for fracture in patients with FD of the proximal femur and could be used to guide implementation of a fracture prevention strategy in these patients.

Injectable demineralized bone matrix particles and their hydrogel bone grafts loaded with β-tricalcium phosphate powder and granules: A comparative study

Demineralized bone matrix (DBM), has been used as a bone-graft material because of its osteoconductivity and osteoinductivity. However, the previous research report that supports the single use of DBM is limited by its rapid resorption caused by the lack of calcium and phosphate. β-Tricalcium phosphate (TCP) is an enriched calcium phosphate material suitable for bone healing with osteoconductive properties. In this study, we have developed injectable bone graft by the loading two kinds of TCP in DBM particles and thermo-sensitive DBM-derived hydrogel (hDBM). TCP powder (pTCP) and TCP granules (gTCP) were loaded into hDBM and DBM, respectively. The bone formation effect was investigated according to the morphological features of TCP. Residual growth factor concentrations were investigated; microstructure and morphology were characterized by SEM. In-vitro studies showed that hDBM/DBM/pTCP and hDBM/DBM/gTCP bone grafts were biocompatible and could promote osteogenesis by up-regulating the expression of Runx2 and OPN, bone-related genes. In-vivo studies using the rabbit-femur defect model revealed that the implanted hDBM/DBM/pTCP bone graft showed similar histology to that of fibrous dysplasia with the expression of CD68, whereas hDBM/DBM/gTCP showed good bone formation. Loading of gTCP in place of pTCP was noticed as an effective way to improve bone regeneration in an injectable hDBM/DBM hydrogel-based bone graft.

Proceedings of the 2022 Santa Fe Bone Symposium: Current Concepts in the Care of Patients with Osteoporosis and Metabolic Bone Diseases

The 22^nd Annual Santa Fe Bone Symposium (SFBS) was a hybrid meeting held August 5-6, 2022, with in-person and virtual attendees. Altogether, over 400 individuals registered, a majority of whom attended in-person, representing many states in the USA plus 7 other countries. The SFBS included 10 plenary presentations, 2 faculty panel discussions, satellite symposia, Bone Health & Osteoporosis Foundation Fracture Liaison Service Boot Camp, and a Project ECHO workshop, with lively interactive discussions for all events. Topics of interest included fracture prevention at different stages of life; how to treat and when to change therapy; skeletal health in cancer patients; advanced imaging to assess bone strength; the state of healthcare in the USA; osteosarcopenia; vitamin D update; perioperative bone health care; new guidelines for managing primary hyperparathyroidism; new concepts on bone modeling and remodeling; and an overview on the care of rare bone diseases, including hypophosphatasia, X-linked hypophosphatemia, tumor induced osteomalacia, osteogenesis imperfecta, fibrodysplasia ossificans progressiva, and osteopetrosis. The SFBS was preceded by the Santa Fe Fellows Workshop on Osteoporosis and Metabolic Bone Diseases, a collaboration of the Endocrine Fellows Foundation and the Osteoporosis Foundation of New Mexico. From the Workshop, 4 participating fellows were selected to give oral presentations at the bone symposium. These proceedings represent the clinical highlights of 2022 SFBS presentations and the discussions that followed, all with the aim of optimizing skeletal health and minimizing the consequences of fragile bones.

Pathological Femoral Shaft Fracture With McCune-Albright Syndrome With Hyperthyroidism Managed With Oral Alendronate: A Case Report

McCune-Albright syndrome (MAS) is a complex endocrinopathy with polyostotic fibrous dysplasia and café-au-lait spots. Pathological femoral shaft fracture along with MAS is not a common occurrence. Bisphosphonates can be used for the management of pathological fractures.

A seven-year-old male child presented with pathological femoral shaft fracture with MAS (café-au-lait macules and hyperthyroidism). The patient was managed conservatively with closed reduction along with hip spica and oral alendronate. Fracture consolidation occurred within six to eight weeks with improvement in bone pains. Oral alendronate can be used as an adjuvant to conservative therapy for pathological fracture in MAS in children.

Effects of zoledronic acid therapy in fibrous dysplasia of bone: a single-center experience

Objective

Fibrous dysplasia (FD) is a rare bone disorder that can involve any part of the skeleton, leading to bone pain, deformities, and fractures. Treatment with intravenous bisphosphonates has been used with variable results. Therefore, we aimed to evaluate the effects of zoledronic acid (ZA) therapy in patients with monostotic or polyostotic FD.

Methods

The medical records of thirteen patients with FD evaluated between 2015 and 2020 were retrospectively analyzed. In the subgroup of patients treated with ZA (n = 7), data on pain relief, changes in bone turnover markers (BTMs), and adverse events following ZA infusions were retrieved. Moreover, radiological changes in response to treatment were recorded in patients who underwent radiological follow-up.

Results

Of the patients, 5 (38%) presented with monostotic whereas 8 (62%) had polyostotic FD. Bone pain was a common finding (69%), and most patients (62%) exhibited elevated baseline BTMs. Partial or complete pain relief was reported in 6 of 7 patients treated with ZA. BTMs, especially C-telopeptide of type I collagen (CTX), significantly decreased after therapy (change rate: -61.8% [IQR -71, -60%]), and median CTX levels were significantly lower than at baseline (0.296 ng/mL [0.216, 0.298] vs. 0.742 ng/mL [0.549, 0.907], respectively; P = 0.04). No radiological improvement was observed in cases with radiological follow-up (n = 3). No serious adverse effects of ZA were reported.

Conclusion

ZA treatment was well tolerated and provided beneficial effects in relieving bone pain and reducing BTMs, especially CTX. Our data reinforce the role of ZA in the treatment of FD-related bone pain.

Case Report: A Neuro-Ophthalmological Assessment of Vision Loss in a Pediatric Case of McCune-Albright Syndrome

Patients diagnosed with McCune-Albright Syndrome (MAS) frequently manifest craniofacial fibrous dysplasia (FD). Craniofacial FD can impinge nerve fibers causing visual loss as well as craniofacial pain. Surgical decompression of affected nerves is performed, with variable efficacy, in an attempt to restore function or alleviate symptoms. Here, we present a case of a 12-year-old MAS patient with visual deficits, particularly in the left eye (confirmed by enlarged blind spots on Goldmann visual field testing), and craniofacial pain. Decompression surgery of the left optic nerve mildly improved vision, while persistent visual deficits were noted at a 3-month follow-up assessment. An in-depth, imaging-based evaluation of the visual system, including the retinal nerve fiber layer, optic nerves, and central nervous system (CNS) visual pathways, revealed multiple abnormalities throughout the visual processing stream. In the current FD/MAS patient, a loss of white matter fiber density within the left optic radiation and functional changes involving the left primary visual cortex were observed. Aberrant structural and functional abnormalities embedded within central visual pathways may play a role in facilitating deficits in vision in FD/MAS and contribute to the variable outcome following peripheral nerve decompression surgery.

Introduction of a Cys360Tyr Mutation in ANO5 Creates a Mouse Model for Gnathodiaphyseal Dysplasia

Gnathodiaphyseal dysplasia (GDD) is a rare autosomal dominant genetic disease characterized by the osteosclerosis of tubular bones and the formation of cemento-osseous lesions in mandibles. Although genetic mutations for GDD have been identified in the ANO5/TMEM16E gene, the cellular and molecular mechanisms behind the pathogenesis of GDD remain unclear. Here, we generated the first knock-in mouse model for GDD with the expression of human mutation p.Cys360Tyr in ANO5. Homozygous Ano5 knock-in mice (Ano5^KI/KI ) replicated GDD-like skeletal features, including massive jawbones, bowing tibia, bone fragility, sclerosis, and cortical thickening of the femoral and tibial diaphysis. Serum alkaline phosphatase (ALP) levels were elevated in Ano5^KI/KI mice as in GDD patients with p.Cys360Tyr mutation. Calvaria-derived Ano5^KI/KI osteoblast cultures showed increased osteoblastogenesis, including hypermineralized bone matrix and enhanced bone formation-related factors expression. Interestingly, Ano5^KI/KI bone marrow-derived macrophage cultures showed decreased osteoclastogenesis, and Ano5^KI/KI osteoclasts exhibited disrupted actin ring formation, which may be associated with some signaling pathways. In conclusion, this new mouse model may facilitate elucidation of the pathogenesis of GDD and shed more light on its treatment. © 2021 American Society for Bone and Mineral Research (ASBMR).

Fibrous dysplasia animal models: A systematic review

BACKGROUND

Fibrous dysplasia (FD) is a rare genetic bone disorder resulting in an overproduction of cAMP leading to a structurally unsound tissue, caused by a genetic mutation in the guanine nucleotide-binding protein gene (GNAS). In order to better understand this disease, several animal models have been developed with different strategies and features.

OBJECTIVE

Conduct a systematic review to analyze and compare animal models with the causative mutation and features of FD.

METHODS

A PRISMA search was conducted in Scopus, PubMed, and Web of Science. Studies reporting an in vivo model of FD that expressed the causative mutation were included for analysis. Models without the causative mutation, but developed an FD phenotype and models of FD cell implantation were included for subanalysis.

RESULTS

Seven unique models were identified. The models were assessed and compared for their face validity, construct validity, mosaicism, and induction methods. This was based on the features of clinical FD that were reported within the categories of: macroscopic features, imaging, histology and histomorphometry, histochemical and cellular markers, and blood/urine markers.

LIMITATIONS

None of the models reported all features of FD and some features were only reported in one model. This made comparing models a challenge, but indicates areas where further research is necessary.

CONCLUSION

The benefits and disadvantages of every model were assessed from a practical and scientific standpoint. While all published reports lacked complete data, the models have nonetheless informed our understanding of FD and provided meaningful information to guide researchers in bench and clinical research.

Genetics and Epigenetics of Bone Remodeling and Metabolic Bone Diseases

Bone metabolism consists of a balance between bone formation and bone resorption, which is mediated by osteoblast and osteoclast activity, respectively. In order to ensure bone plasticity, the bone remodeling process needs to function properly. Mesenchymal stem cells differentiate into the osteoblast lineage by activating different signaling pathways, including transforming growth factor β (TGF-β)/bone morphogenic protein (BMP) and the Wingless/Int-1 (Wnt)/β-catenin pathways. Recent data indicate that bone remodeling processes are also epigenetically regulated by DNA methylation, histone post-translational modifications, and non-coding RNA expressions, such as micro-RNAs, long non-coding RNAs, and circular RNAs. Mutations and dysfunctions in pathways regulating the osteoblast differentiation might influence the bone remodeling process, ultimately leading to a large variety of metabolic bone diseases. In this review, we aim to summarize and describe the genetics and epigenetics of the bone remodeling process. Moreover, the current findings behind the genetics of metabolic bone diseases are also reported.

Periorbital inflammation associated with craniofacial fibrous dysplasia: Report of three cases and review of the literature

Fibrous dysplasia (FD) is a mosaic skeletal disorder in which the craniofacial bones are commonly affected. Normal structures are replaced by expansile, highly vascular, fibro-osseous tissue. The typical clinical course is a gradual, asymptomatic expansion of the osseous structures. However, in the periorbital region, even minor structural changes may cause functional impairment, such as diplopia and hyposmia. Furthermore, rapidly evolving secondary lesions, such as fluid-filled cysts, can sometimes develop. In the midface and periorbital regions, such acute change may be associated with severe pain, vision loss, and, signs of inflammation. Here we describe three patients with craniofacial FD who presented with recurrent episodes of periorbital inflammation mimicking orbital cellulitis. All presented with pain, edema, erythema, and warmth, with varying degrees of functional impairment. On imaging, all had cystic changes in the FD lesion, including two with aneurysmal bone cysts (ABCs). Two were initially diagnosed with periorbital cellulitis and treated with antibiotics; in two, the radiographic findings were misdiagnosed as osteomyelitis. Recurrent episodes were recognized as not infectious and effectively managed with corticosteroids. Given the vascular nature of FD and the association of ABCs, it is likely the findings in these patients represent inflammation associated with vascular leak in the relatively confined space of the tissues overlying the periorbital bones. Recognition of this entity can lead to more rapid and appropriate treatment.

Chondrosarcoma arising in monostotic fibrous dysplasia treated with total femur resection and megaprothesis: A case report

INTRODUCTION

Fibrous dysplasia is tumor like lesions of bone which develop as substitution of bone by an expansion of fibrous connective tissue mixed with hard trabeculae. Chondrosarcomas is one of common malignant primary bone tumor derived from heterogenous group of neoplasm producing chondroid matrix. Chondrosarcoma arising in fibrous dysplasia, especially in monostotic fibrous dysplasia is a very rare case.

CASE REPORT

A 54-year-old male presented with chief complaint of pain on left thigh. Patient with history of pathological fracture on left femoral diaphysis 3 years ago due to fibrous dysplasia and had underwent curettage, open reduction, and internal fixation at other hospital. Plain radiography revealed expansive lytic lesion, interrupted periosteal reaction with plate and screw attached to the lesion, and soft tissue mass. MRI T2FS sequence showed hyperintense mass extending from subtrochanteric to distal of left femoral diaphysis. Histopathological result from biopsy suggested chondrosarcoma.

CONCLUSIONS

Malignant transformation of monostotic type was less frequently compared to polyostotic type. Among all malignant transformation cases, alteration to chondrosarcoma was more scarce than other malignancy such as osteosarcoma and fibrosarcoma. Wide surgical margin and reconstruction in chondrosarcoma provide good local control and functional outcome.

Assessing bone formation in patients with chronic kidney disease using procollagen type I N-terminal propeptide (PINP): The choice of assay makes a difference

BACKGROUND

Measurement of procollagen type I N-terminal propeptide (PINP) concentration in serum reflects the rate of type I collagen synthesis and can therefore be used as a bone formation marker. There are two methods of PINP quantification; the first measures the trimeric propeptide (intact PINP) and the second measures both the trimeric and monomeric propeptides (total PINP). Trimeric PINP is excreted via hepatic endothelial cells, whereas monomeric PINP is cleared renally. Therefore, in renal failure, the total assay has a positive bias with respect to the intact assay, due to monomeric PINP accumulation. The aim of this study was to compare the performance of both assays across all stages of chronic kidney disease.

METHODS

Serum was taken from male (n = 111) and female (n = 105) patients attending a metabolic bone clinic, and these were partitioned into stages of chronic kidney disease 1-5. Each serum sample was analysed using the Roche electrochemiluminescence immunoassay for total PINP and the Immunodiagnostic Systems chemiluminescence immunoassay for intact PINP.

RESULTS

Passing-Bablok regression analysis comparing both methods showed that with advancing chronic kidney disease there was a proportional positive bias affecting the total assay when compared with the intact assay. This proportional positive bias was statistically significant for chronic kidney disease stages 3b, 4 and 5.

CONCLUSIONS

Based on this method comparison study, usage of the total PINP assay should be avoided in chronic kidney disease stages 3b, 4 and 5 (eGFR ≤44 mL/min/1.73 m²) and instead an intact assay used as the total assay overestimates PINP concentrations due to monomeric PINP accumulation.

Regression of fibrous dysplasia in response to denosumab therapy: A report of two cases

We present two patients with fibrous dysplasia who showed a decrease in lesional size and activity after denosumab therapy. Both patients also experienced a reduction in pain and bone turnover markers, which had not been accomplished during previous bisphosphonate therapy. These cases highlight the potential of denosumab to decrease lesional size in fibrous dysplasia. This finding has been reported in mice, but not in humans. Denosumab may be considered when bisphosphonates are not tolerated or not effective (enough), or in severe cases as neoadjuvant therapy to improve surgical possibilities and outcome. In addition, these results show that Na[¹⁸F]F PET-CT is suitable for detecting change in each fibrous dysplasia lesion distinctively.

Rare Diseases of the Middle Ear and Lateral Skull Base

Otalgia, otorrhea and hearing loss are the most common ear-related symptoms that lead to the consultation of an otolaryngologist. Furthermore, balance disorders and affections of the cranial nerve function may play a role in the consultation. In large academic centres, but also in primary care, the identification of rare diseases of the middle ear and the lateral skull base is essential, as these diseases often require interdisciplinary approaches to establish the correct diagnosis and to initiate safe and adequate treatments. This review provides an overview of rare bone, neoplastic, haematological, autoimmunological and infectious disorders as well as malformations that may manifest in the middle ear and the lateral skull base. Knowledge of rare disorders is an essential factor ensuring the quality of patient care, in particular surgical procedures. Notably, in untypical, complicated, and prolonged disease courses, rare differential diagnoses need to be considered.

Congenital Conditions of Hypophosphatemia in Children

Great strides over the past few decades have increased our understanding of the pathophysiology of hypophosphatemic disorders. Phosphate is critically important to a variety of physiologic processes, including skeletal growth, development and mineralization, as well as DNA, RNA, phospholipids, and signaling pathways. Consequently, hypophosphatemic disorders have effects on multiple systems, and may cause a variety of nonspecific signs and symptoms. The acute effects of hypophosphatemia include neuromuscular symptoms and compromise. However, the dominant effects of chronic hypophosphatemia are the effects on musculoskeletal function including rickets, osteomalacia and impaired growth during childhood. While the most common causes of chronic hypophosphatemia in children are congenital, some acquired conditions also result in hypophosphatemia during childhood through a variety of mechanisms. Improved understanding of the pathophysiology of these congenital conditions has led to novel therapeutic approaches. This article will review the pathophysiologic causes of congenital hypophosphatemia, their clinical consequences and medical therapy.

Kyphotic deformity of the lumbar spine due to a monostotic fibrous dysplasia of the second lumbar vertebra: a case report and its surgical management

Monostotic fibrous dysplasia (MFD) of the lumbar spine represents an exceedingly rare lesion. A 26-year-old patient presented with a progressive osteolytic lesion of the vertebral body L2 and the diagnosis of MFD. A minimally invasive left-sided eXtreme Lateral Interbody Fusion (XLIF) approach with resection of the vertebral body L2 with placement of a mesh cage was performed. No complications were observed perioperatively and the symptoms rapidly improved. Minimally invasive piecemeal resection with a combined dorsolateral approach showed a favorable clinical and radiological outcome and seems to be a safe and reliable technique for MFD.

Imaging of advanced craniofacial fibrous dysplasia associated with McCune-Albright syndrome: A case report

The fibrous dysplasia of bone is painless, benign, and slowly progressive bone lesion. It may rarely become aggressive by compression of adjacent organs or malignant transformation. This disease falls within the scope of a McCune-Albright syndrome in less than 7 % of cases. The authors reported the case of a 25-year-old woman, living in the countryside, who suffered from a severe craniofacial fibrous dysplasia which has begun since her childhood with no medical care. Her clinical picture was that of McCune-Albright syndrome, and CT scan revealed advanced dysplasia with endocranial compression.

Radiographic Follow-Up of Fibrous Dysplasia in 138 Patients

OBJECTIVE. The purpose of this study was to explore the temporal changes in fibrous dysplasia (FD) at radiographic follow-up. MATERIALS AND METHODS. A total of 138 patients with FD who had undergone extremity radiography at least twice with a minimum 12-month interval between examinations were enrolled in this study. FD was monostotic in 99 patients and polyostotic in 39 patients. Patients were also classified according to skeletal maturity as follows: Patients 16 years old or younger were classified in the skeletally immature group (n = 34), and patients 17 years old or older were classified in the skeletally mature group (n = 104). We compared the initial and follow-up radiographs for the following findings: lesion size, opacity, sclerotic rim, calcification, and trabeculation. RESULTS. Of the 138 patients, radiographic follow-up showed no change in lesion size in 101 patients (73.2%), progression in 31 (22.5%), and regression in six (4.3%). FD in immature bones progressed more often than FD in mature bones (23/34 [67.6%] vs 8/104 [7.7%], respectively; p = 0.000), and polyostotic FD had a greater chance of regressing than monostotic FD (4/39 [10.3%] vs 2/99 [2.0%]; p = 0.032). A temporal change in FD lesion opacity was noticed in a minority of patients (19/138, 13.8%). Variable changes were observed in the sclerotic rim, calcification, and trabeculation. CONCLUSION. The radiographic follow-up of FD showed that approximately a quarter of lesions changed in size over time. Regardless of the change in lesion size, opacity and several morphologic features of FD changed during the follow-up period, which might reflect the histopathologic evolution of FD.

Fibrous Dysplasia/McCune-Albright Syndrome: A Rare, Mosaic Disease of Gα s Activation

Fibrous dysplasia/McCune-Albright syndrome (FD/MAS) is a rare disorder of striking complexity. It arises from somatic, gain-of-function mutations in GNAS, leading to mosaic Gα s activation and inappropriate production of intracellular cyclic adenosine monophosphate (cAMP). The clinical phenotype is largely determined by the location and extent of affected tissues, and the pathophysiological effects of Gα s activation within these tissues. In bone, Gα s activation results in impaired differentiation of skeletal stem cells, leading to discrete skeletal lesions prone to fracture, deformity, and pain. Extraskeletal manifestations include a variable combination of hyperpigmented macules and hyperfunctioning endocrinopathies. Distinctive age-related changes in disease development has key effects on histologic, radiographic, and clinical features. FD/MAS thus presents along a uniquely broad clinical spectrum, and the resulting challenges in diagnosis and management can be difficult for clinicians. This review presents FD/MAS in the context of a mosaic disorder of Gα s activation, providing an intellectual framework within which to understand, evaluate, and treat this interesting disease. It includes a comprehensive summary of current understanding of FD/MAS pathogenesis, and a detailed discussion of clinical presentation and management. Critical areas of unmet need are highlighted, including discussion of key challenges and potential solutions to advance research and clinical care in FD/MAS.