Long Bone Fractures in Fibrous Dysplasia/McCune-Albright Syndrome: Prevalence, Natural History, and Risk Factors

Incidence and Prevalence of Fibrous Dysplasia/McCune-Albright Syndrome: A Nationwide Registry-Based Study in Denmark

CONTEXT

Fibrous dysplasia/McCune-Albright syndrome (FD/MAS) is a rare genetic disorder. Incidence and prevalence are not well-studied. Epidemiological research is complicated by the rarity of FD/MAS, absence of registries, heterogeneous presentation, and possibly asymptomatic phenotype. FD/MAS may present with FGF23-mediated hypophosphatemia, of which the epidemiology is also unclear.

OBJECTIVE

Evaluate incidence and prevalence of FD/MAS and FD/MAS-related hypophosphatemia.

METHODS

This cohort study based on the nationwide Danish National Patient Registry from 1995-2018, included patients identified by ICD-10 codes M85.0 (monostotic FD [MFD]) and Q78.1 (polyostotic FD [PFD]/MAS). Incidence rates and prevalence were calculated and stratified by sex, age, calendar period, and diagnosis code. Cases were screened for FD-associated hypophosphatemia by diagnosis code E.83 (disorder of mineral metabolism) and dispatched vitamin D analogues.

RESULTS

A total of 408 patients were identified, 269 with MFD (66%), 139 with PFD/MAS (34%), comparable between sexes. Incidence of FD/MAS demonstrated increasing secular trend with a rate of 3.6 per 1 000 000 person-years (95% CI: 2.9, 4.5) in 2015-2018. Incidence peaked between age 11 and 20. Prevalence of FD/MAS increased over time to 61.0 (95% CI: 54.6, 67.4) per 1 000 000 persons in 2018. The incidence rate of MFD was 1.5-fold that of PFD/MAS in the first decade, rising to 2.5-fold in the last decade. No FD/MAS cases were registered with diagnosis code or treatment for hypophosphatemia.

CONCLUSION

FD/MAS is rare, diagnosis peaks during adolescence without sex predominance, and MFD is most prevalent. Hypophosphatemia may be underdiagnosed and undertreated, or it may be underregistered, comparing this study to literature.

Serum Phosphorus as a Driver of Skeletal Morbidity in Fibrous Dysplasia

CONTEXT

Fibrous dysplasia (FD) results in fractures, pain, and deformities. Abnormal osteoprogenitor cells overproduce FGF23, leading to hyperphosphaturia in most patients and frank hypophosphatemia in a subset. Studies suggest hypophosphatemia is associated with increased FD-related morbidity. However, the relationship between phosphorus and skeletal complications has not been investigated, and the optimal therapeutic target has not been determined.

OBJECTIVE

Characterize the impact of serum phosphorus on FD-related morbidity and identify levels associated with increased skeletal complications.

METHODS

Natural history study with 240 subjects at a clinical research center who had ≥1 fasting phosphorus level, determined as age- and sex-adjusted Z-scores. Subjects were categorized based on frank hypophosphatemia (Z-score ≤ -2; n = 48); low-normophosphatemia (> -2 to ≤ -1; n = 66); and high-normophosphatemia (> -1 to ≤ 2; n = 125). Main outcomes were fractures, orthopedic surgeries, and scoliosis.

RESULTS

Subjects with frank and low-normophosphatemia had increased fracture and surgery rates vs high-normophosphatemia. The prevalence of moderate to severe scoliosis was similarly higher in the frank and low-normophosphatemia groups. In a subanalysis of patients matched for Skeletal Burden Score ≥35, fracture and surgery rates remained higher in the frank hypophosphatemia group, suggesting association between phosphorus and skeletal complications is not explained by differences in FD burden alone.

CONCLUSION

Both frank hypophosphatemia and low-normophosphatemia are associated with increased FD-related complications. This supports FGF23-mediated hypophosphatemia as a driver of skeletal morbidity, which may impact a larger proportion of the FD/McCune-Albright syndrome population than previously recognized. These findings enable clinicians to identify at-risk patients and will inform development of prospective studies to determine optimal therapeutic targets.

Phenotyping Pain in Patients With Fibrous Dysplasia/McCune-Albright Syndrome

CONTEXT

Pain is a poorly managed aspect in fibrous dysplasia/McCune-Albright syndrome (FD/MAS) because of uncertainties regarding the clinical, behavioral, and neurobiological underpinnings that contribute to pain in these patients.

OBJECTIVE

Identify neuropsychological and neurobiological factors associated with pain severity in FD/MAS.

DESIGN

Prospective, single-site study.

PATIENTS

Twenty patients with FD/MAS and 16 age-sex matched healthy controls.

INTERVENTION

Assessments of pain severity, neuropathic pain, pain catastrophizing (pain rumination, magnification, and helplessness), emotional health, and pain sensitivity with thermal quantitative sensory testing. Central nervous system (CNS) properties were measured with diffusion tensor imaging, structural magnetic resonance imaging, and functional magnetic resonance imaging.

MAIN OUTCOME MEASURES

Questionnaire responses, detection thresholds and tolerances to thermal stimuli, and structural and functional CNS properties.

RESULTS

Pain severity in patients with FD/MAS was associated with more neuropathic pain quality, higher levels of pain catastrophizing, and depression. Quantitative sensory testing revealed normal detection of nonnoxious stimuli in patients. Individuals with FD/MAS had higher pain tolerances relative to healthy controls. From neuroimaging studies, greater pain severity, neuropathic pain quality, and psychological status of the patient were associated with reduced structural integrity of white matter pathways (superior thalamic radiation and uncinate fasciculus), reduced gray matter thickness (pre-/paracentral gyri), and heightened responses to pain (precentral, temporal, and frontal gyri). Thus, properties of CNS circuits involved in processing sensorimotor and emotional aspects of pain were altered in FD/MAS.

CONCLUSION

These results offer insights into pain mechanisms in FD/MAS, while providing a basis for implementation of comprehensive pain management treatment approaches that addresses neuropsychological aspects of pain.

Fibrous dysplasia in children and its management

PURPOSE OF REVIEW

The purpose of this review is to provide a comprehensive overview into the diagnosis and management of fibrous dysplasia (FD) in children.

RECENT FINDINGS

FD is a mosaic disorder arising from somatic Gα s variants, leading to impaired osteogenic cell differentiation. Fibro-osseous lesions expand during childhood and reach final disease burden in early adulthood. The mainstay of treatment focuses on surgical correction of skeletal deformities, physiatric care, and medical management of associated hyperfunctioning endocrinopathies. Bisphosphonates may be helpful to treat bone pain, but do not alter lesion quality or progression. Emerging evidence suggests that the RANKL inhibitor denosumab may be effective in improving lesion activity and mineralization, however further studies are needed to determine the potential utility of this and other novel therapies, particularly in children with FD.

SUMMARY

Management of children with FD has unique challenges related to skeletal growth and age-related lesion progression. Inclusion of children in clinical research is critical to develop effective treatment strategies to treat FD lesions and prevent their development.

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.

Clinical value of RANKL, OPG, IL-6 and sclerostin as biomarkers for fibrous dysplasia/McCune-Albright syndrome

BACKGROUND

Fibrous dysplasia/McCune-Albright syndrome (FD/MAS) is a rare genetic bone disease caused by a somatic mutation in the GNAS gene. Currently used bone turnover markers (BTMs) do not correlate with the clinical picture and are not useful to predict or monitor therapy success. This study assessed the correlation of RANKL, OPG, RANKL/OPG ratio, IL-6 and sclerostin with the classic BTMs alkaline phosphatase (ALP), procollagen type 1 propeptide (P1NP) and beta crosslaps (CTX), with pain, skeletal burden score (SBS) and response to bisphosphonate or denosumab treatment.

METHODS

Ninety-six serum samples of adult patients >18 years of age with any subtype of FD/MAS were included from the biobank facility of the Leiden University Medical Center, Center for Bone Quality between 2015 and 2021. Standard laboratory assessments were assessed as part of usual care. The concentrations of potential biomarkers RANKL, OPG, sclerostin, IL-6 were analyzed. Data on FD/MAS subtype, age, pain, treatment history and treatment response were retrieved from the electronic patient files. Baseline characteristics were summarized by descriptive statistics. Correlations of the concentrations of the potential biomarkers with classic bone turnover markers, SBS and pain scores were cross-sectionally assessed by Spearman rank order correlation. Correction for multiple testing was performed by Benjamini and Hochberg False Discovery Rate. A sensitivity analyses was performed by excluding patients with SBS below 15 and patients using antiresorptive medication at the time of blood withdrawal or within the wash-out period. In patients treated with bisphosphonates or denosumab after blood withdrawal, pre-treatment concentrations were compared in patients with and without therapy response by Mann Whitney U test.

RESULTS

The median age of the patients was 41.2 (Q1-Q3 25.9-52.2) years, 62.5 % was female. Median SBS was 2.5 (Q1-Q3 0.5-7.8). RANKL level correlated weakly with ALP (Spearman rho 0.309, p = 0.004, n = 84), but not with P1NP or CTX. The RANKL/OPG ratio, OPG, IL-6 and sclerostin did not correlate with ALP, P1NP or CTX. None of the potential biomarkers correlated with SBS or pain. Results of the sensitivity analyses were comparable. Pre-treatment biomarker levels were similar in patients with and without improvement in pain scores following bisphosphonate therapy. Pre-treatment RANKL and sclerostin were comparable between patients with and without improvement in pain scores after denosumab therapy. Pre-treatment IL-6 level and the RANKL/OPG ratio seemed to be higher in patients with response to denosumab (IL-6: median 0.64 (Q1-Q3 0.53-0.74) pg/mL, n = 6, RANKL/OPG: median 0.062 (Q1-Q3 0.016-0.331), n = 5) compared to patients without response (IL-6: median 0.35 (0.20-0.54) pg/mL, n = 5, RANKL/OPG: 0.027 (0.024-0.046), n = 4). Pre-treatment IL-6 correlated with the improvement in maximum pain scores (rho 0.962, p < 0.001, n = 9) and average pain scores (rho 0.895, p = 0.001, n = 9) reported during denosumab therapy.

CONCLUSION

Increased concentrations of RANKL, IL-6, sclerostin and of the RANKL/OPG ratio do not indicate severity of FD/MAS, as no correlation was observed of these potential biomarkers with the classic BTMs and SBS. Biomarker levels did not correlate with pain and had no value in predicting bisphosphonate treatment response. These biomarkers are not superior over the currently used methods of assessing ALP, P1NP and CTX or evaluating SBS to establish disease extent or activity and provide no reliable results. Yet, possibly pre-treatment IL-6 and the RANKL/OPG ratio may have some predictive value for clinical response to denosumab. Therefore, studies investigating disease activity and treatment response should include lesional imaging and patient-reported outcome measures.

Skeletal Disease Acquisition in Fibrous Dysplasia: Natural History and Indicators of Lesion Progression in Children

Fibrous dysplasia (FD) is a rare mosaic disorder resulting in fractures, pain, and disability. Bone lesions appear during childhood and expand during skeletal growth. The rate at which FD lesions progress and the biochemical determinants of FD lesion formation have not been established, making it difficult to investigate and implement preventative therapies. The purpose of this study was to characterize FD lesion progression in children, and to identify clinical variables associated with progressive disease. Clinical data and imaging from an ongoing natural history study at the National Institutes of Health (NIH) were reviewed. 99m-Technetium methylene diphosphonate (99Tc-MDP) scans were used to determine Skeletal Burden Score (SBS), a validated quantitative scoring system. FD progression rate was determined by the change in the SBS in each patient per year. Thirty-one children had serial 99Tc-MDP scans, with a median age at first scan of 6 years (interquartile range [IQR] 4-8, range 2-10), and median follow-up 1.1 years (IQR 1.1-2.1, range 0.7-11.2). The median FD progression rate for the total group was 2.12 SBS units/year (IQR 0.81-2.94, range 0.05-7.81). FD progression rates were highest in children under age 8 years and declined with age (p = 0.03). Baseline disease severity was associated with subsequent disease progression (p = 0.009), with the highest FD progression rates in patients with moderate disease (baseline SBS 16-30), and lowest progression rates in those with severe disease (SBS ≥50). Serum levels of the bone formation marker osteocalcin were positively correlated with subsequent FD progression rate (p = 0.01, R = 0.58). There was no association between FD progression and baseline endocrinopathies, fractures, or surgery rates. FD lesions progress during childhood, particularly in younger children and those with moderate involvement. Osteocalcin may potentially serve as a biomarker for progressive disease. These findings may allow clinicians to investigate preventative therapies, and to identify children with FD who are candidates for early interventions. Published 2022. This article is a U.S. Government work and is in the public domain in the USA.

Postoperative thyroid crisis in an 11-year old male with McCune-Albright syndrome and atypical triiodothyronine hyperthyroidism: A case report

RATIONALE

McCune-Albright syndrome (MAS) is a rare heterogeneous clinical disease caused by sporadic, somatic, and postzygotic mutations. Thyroid crisis is even rare in patients with MAS, and we report the clinical outcomes of the first case of a MAS patient with atypical triiodothyronine (T3) hyperthyroidism who developed thyroid crisis after orthopedic surgery.

PATIENT CONCERNS

The patient with MAS and atypical T3 hyperthyroidism was an 11-year-old man who had undergone surgery for a right femur fracture and shepherd bending deformity. His main symptoms were dizziness, nausea, and vomiting with elevated body temperature because of developed thyroid crisis. Thyroid function tests showed high T3 and remarkably high free T3 levels, and remarkably increased thyrotropin level, but unchanged thyroxine and free thyroxine levels.

DIAGNOSIS

The patient was diagnosed with postoperative thyroid crisis following surgery for a right femur fracture, shepherd bending deformity, and MAS with atypical T3 hyperthyroidism.

INTERVENTIONS

Propranolol was intravenously administered. The therapy included intravenous hydrocortisone, a saturated solution of potassium iodine and propylthiouracil, and continuous physical cooling.

OUTCOMES

The patient was discharged after achieving a stable condition with normal thyroid and liver function after surgery because of active anti-thyroid crisis treatment.

LESSONS

The operation of such patients should focus on the pre-operative heart rate, platelet level, and thyroid hormone levels. Abnormal values should be adjusted to the normal range, and such patients should achieve complete hemostasis and transfuse with blood following surgery anemia.