Spontaneous vertebral fractures after denosumab discontinuation: A case collection and review of the literature

Prevention and Management of Denosumab Discontinuation Rebound Fractures

Denosumab rebound-associated fractures occur in approximately 1 out of 14 patients who discontinue denosumab therapy without sequential antiresorptive therapy. They occur due to excessive bone resorption after missed or delayed denosumab doses. The fractures are multiple and quality of life altering. This phenomenon occurs in all patient populations that use prolonged denosumab therapy. Average delay in denosumab dosing beyond 7 months or discontinuation of denosumab without sequential therapy is associated with increased mortality in retrospective studies. Multiple medication regimens used after the end of denosumab therapy have been shown to substantially reduce the risk of rebound vertebral fractures.

On-time denosumab dosing recovered rapidly during the COVID-19 pandemic, yet remains suboptimal

Timely administration of denosumab every 6 mo is critical in osteoporosis treatment to avoid multiple vertebral fracture risk upon denosumab discontinuation or delay. This study aimed to estimate the immediate and prolonged impact of the COVID-19 pandemic on the timing of denosumab doses. We identified older adults (≥66 yr) residing in the community who were due to receive denosumab between January 2016 and December 2020 using Ontario Drug Benefit data. We completed an interrupted time-series analysis to estimate the impact of the COVID-19 pandemic (March 2020) on the monthly proportion of on-time denosumab doses (183 +/-30 d). Analyses were stratified by user type: patients due for their second dose (novice users), third or fourth dose (intermediate users), or ≥5th dose (established users). In additional analyses, we considered patients living in nursing homes, switching to other osteoporosis drugs, and reported trends until February 2022. We studied 148 554 patients (90.9% female, mean [SD] age 79.6 [8.0] yr) receiving 648 221 denosumab doses. The average pre-pandemic proportion of on-time therapy was steady in the community, yet differed by user type: 64.9% novice users, 72.3% intermediate users, and 78.0% established users. We identified an immediate overall decline in the proportion of on-time doses across all user types at the start of the pandemic: -17.8% (95% CI, -19.6, -16.0). In nursing homes, the pre-pandemic proportion of on-time therapy was similar across user types (average 83.5%), with a small decline at the start of the pandemic: -3.2% (95% CI, -5.0, -1.2). On-time therapy returned to pre-pandemic levels by October 2020 and was not impacted by therapy switching. Although on-time dosing remains stable as of February 2022, approximately one-fourth of patients in the community do not receive denosumab on-time. In conclusion, although pandemic disruptions to denosumab dosing were temporary, levels of on-time therapy remain suboptimal.

Methodological guidance for the use of real-world data to measure exposure and utilization patterns of osteoporosis medications

Observational studies of osteoporosis medications can provide critical real-world evidence (RWE) that fills knowledge gaps left by clinical trials. However, careful consideration of study design is needed to yield reliable estimates of association. In particular, obtaining valid measurements of exposure to osteoporosis medications from real-world data (RWD) sources is complicated due to different medication classes, formulations, and routes of administration, each with different pharmacology. Extended half-lives of bisphosphonates and extended dosing of denosumab and zoledronic acid require particular attention. In addition, prescribing patterns and medication taking behavior often result in gaps in therapy, switching, and concomitant use of osteoporosis therapies. In this review, we present important considerations and provide specialized guidance for measuring osteoporosis drug exposures in RWD. First, we compare different sources of RWD used for osteoporosis drug studies and provide guidance on identifying osteoporosis medication use in these data sources. Next, we provide an overview of osteoporosis pharmacology and how it can influence decisions on exposure measurement within RWD. Finally, we present considerations for the measurement of osteoporosis medication exposure, adherence, switching, long-term exposures, and drug holidays using RWD. Ultimately, a thorough understanding of the differences in RWD sources and the pharmacology of osteoporosis medications is essential to obtain valid estimates of the relationship between osteoporosis medications and outcomes, such as fractures, but also to improve the critical appraisal of published studies.

Anti-Siglec-15 Antibody Prevents Marked Bone Loss after Acute Spinal Cord Injury-Induced Immobilization in Rats

Rapid and extensive sublesional bone loss after spinal cord injury (SCI) is a difficult medical problem that has been refractory to available interventions except the antiresorptive agent denosumab (DMAB). While DMAB has shown some efficacy in inhibiting bone loss, its concurrent inhibition of bone formation limits its use. Sialic acid-binding immunoglobulin-like lectin (Siglec)-15 is expressed on the cell surface of mature osteoclasts. Anti-Siglec-15 antibody (Ab) has been shown to inhibit osteoclast maturation and bone resorption while maintaining osteoblast activity, which is distinct from current antiresorptive agents that inhibit the activity of both osteoclasts and osteoblasts. The goal of the present study is to test a Siglec-15 Ab (NP159) as a new treatment option to prevent bone loss in an acute SCI model. To this end, 4-month-old male Wistar rats underwent complete spinal cord transection and were treated with either vehicle or NP159 at 20 mg/kg once every 2 weeks for 8 weeks. SCI results in significant decreases in bone mineral density (BMD, -18.7%), trabecular bone volume (-43.1%), trabecular connectivity (-59.7%), and bone stiffness (-76.3%) at the distal femur. Treatment with NP159 almost completely prevents the aforementioned deterioration of bone after SCI. Blood and histomorphometric analyses revealed that NP159 is able to greatly inhibit bone resorption while maintaining bone formation after acute SCI. In ex vivo cultures of bone marrow cells, NP159 reduces osteoclastogenesis while increasing osteoblastogenesis. In summary, treatment with NP159 almost fully prevents sublesional loss of BMD and metaphysis trabecular bone volume and preserves bone strength in a rat model of acute SCI. Because of its unique ability to reduce osteoclastogenesis and bone resorption while promoting osteoblastogenesis to maintain bone formation, Siglec-15 Ab may hold greater promise as a therapeutic agent, compared with the exclusively antiresorptive or anabolic agents that are currently used, in mitigating the striking bone loss that occurs after SCI or other conditions associated with severe immobilization. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Denosumab treatment lapses, discontinuation, and off-treatment fracture risk: A retrospective study of patients with osteoporosis in a real-world clinical setting

INTRODUCTION

The purpose of this study was to retrospectively examine predictors of fracture risk when adult patients experienced a denosumab treatment lapse or discontinuation in a real-world clinic setting.

MATERIALS AND METHODS

Eligible patients were adults who had received ≥2 doses of denosumab at an academic health center in the United States. Demographics, treatment doses, reasons for missed doses, and fractures, were collected retrospectively from electronic health records, from an 8-year period (2010-2018). The number of times each patient incurred a treatment lapse, defined as ≥240 days between two doses (excluding lapse due to discontinuation, death, or transfer of care) was computed. The occurrence of denosumab discontinuation (excluding discontinuation due to death or transfer of care), whether the patient initiated alternative therapy, and the reason for each lapse and discontinuation were collected. Cox proportional hazards models assessed characteristics associated with risk of fracture and treatment discontinuation. A logistic regression model was used to determine if cumulative amount of time off medication (i.e., cumulative lapse time) was associated with a higher likelihood of incurring a fracture.

RESULTS

We included 534 patients: 95 % White, 86 % women, 33 % tobacco users, 13 % diagnosed with diabetes, median age 69 years (Interquartile Range (IQR): 62-77), and median Body Mass Index (BMI) 25 kg/m2 (IQR: 22-28). Thirty-six percent of patients incurred 250 lapses; 10 % discontinued therapy. Dental problems/procedures and logistical barriers were the most common reasons for lapses and discontinuations. Nineteen percent (n = 103) incurred a total of 190 fractures; of these, 121 were osteoporotic, 50 were vertebral. Risk of any, osteoporotic, and vertebral fractures were associated with off-treatment status (hazard ratio [HR] = 1.7, p = 0.043; HR = 2.0, p = 0.026; and HR = 4.2, p = 0.001, respectively) and older age (HR = 1.3, p = 0.015; HR = 1.5, p = 0.001; and HR = 1.8, p = 0.005, respectively). Older age was associated with higher risk of discontinuation (HR = 1.4, p = 0.022). There was a non-significant trend of a nonlinear association between incurring a fracture and cumulative lapse time (p = 0.087).

CONCLUSION

Denosumab treatment lapses are common, and off-treatment status may be associated with a higher risk of fractures. Clinical teams should proactively identify and address adverse effects and potential logistical barriers to reduce the risk of treatment lapses.

Effect of low dose denosumab on bone mineral density in postmenopausal women with osteoporosis after a transition from 60 mg dose: a prospective observational study

INTRODUCTION

Denosumab is an effective antiresorptive molecule and reduces the risk of fracture in postmenopausal osteoporosis. Cessation of denosumab therapy however is associated with rapid declines in bone mineral density (BMD), rises in bone remodeling, and an increased risk of fracture. We evaluated the effect of low dose denosumab (30 mg every 6 months) on the prevention of bone loss following a switch from standard dose (60 mg of denosumab every 6 months) in a prospective observational study.

METHODS

We recruited 114 women 50-90 years of age with postmenopausal osteoporosis at a moderate fracture risk without prior fragility fractures, who had been on denosumab 60 mg every 6 month. These women switched to low dose denosumab 30 mg every 6 months. Mean percentage change in lumbar spine (LS), femoral neck (FN), total hip (TH) and 1/3 distal radius (1/3RAD) BMD at 12 and 24 months were evaluated. Predictors for change in BMD were explored. Subgroup analysis for patients on denosumab 60 mg every 6 months for <3 years and for ≥3 years before switching to low dose denosumab 30 mg was evaluated.

RESULTS

At 12 months following a switch from 60 mg to 30 mg of denosumab every 6 months we observed an increase in LS BMD mean percentage change (+2.03%, 95% CI 1.18-2.88, p < 0.001). BMD was stable at the hip and radial sites. Age was found to be a predictor of the mean percentage change in LS BMD for the overall sample. At 24 months, there was a further increase in LS BMD mean percentage change (+3.44%, 95% CI 1.74-5.12, p < 0.001), with stable BMD at other skeletal sites. The 12 month mean BMD percentage change at the LS (p = 0.015), FN (p < 0.001), TH (p < 0.001), and 1/3 RAD (p < 0.001) were found to be predictors of the 24 month mean BMD percentage change. No clinical fractures were reported during 24 months of follow up.

CONCLUSION

We observed stable BMD following a switch from denosumab 60 mg every 6 months to 30 mg every 6 months in this prospective observational study conducted in postmenopausal women at a moderate fracture risk.

Maintenance of bone resorption markers in the low premenopausal range during the year following denosumab discontinuation is associated to bone density preservation. The ReoLaus study

PURPOSE

Denosumab discontinuation (DD) is associated with serum C-terminal X-linked telopeptides (sCTX) increase, bone mineral density (BMD) loss and vertebral fractures (VFs) risk increase. We compared clinical characteristics of women losing or not lumbar spine (LS) BMD one-year after DD, and their sCTX values at different time-points.

METHODS

We included women from the ReoLaus cohort having received ≥2 denosumab 60 mg injections, with three BMD measurements on the same device (before (DXA1), at the end of denosumab treatment (DXA2), and one-year after (DXA3)) and sCTX measured at different time-points. Losers (LS DXA3-DXA2 > 2.8 %) and stable groups were compared.

RESULTS

63 postmenopausal women were included (mean age 64.2 ± 9.1 years, 7.9 ± 2.7 denosumab injections). 19 months after last denosumab injection, 65 % had lost LS BMD. Losers were younger, had lower BMD and higher sCTX before denosumab, received more injections and gained more BMD under denosumab, and had higher sCTX after DD. Same proportion of patients received bisphosphonates in both groups, but 11 (all in losers group) received ≥1 zoledronate infusion. Three women developed VFs in the losers group (none in the stable). Mean sCTX at 10 and 19 months were 590 ± 372 versus 221 ± 101, and 598 ± 324 versus 293 ± 157 ng/l, respectively (premenopausal range < 573 ng/l, p < 0.01 for both). LS BMD loss and sCTX levels measured at 10 and 19 months were correlated (r² = 0.29, p = 0.10, and r² = 0.16, p < 0.005).

CONCLUSION

Maintenance of BMD gained with denosumab is associated with sCTX in the low premenopausal range after DD. Whether this could be achieved by regular sCTX monitoring and adjustment of bisphosphonates doses or frequency administration needs to be confirmed by further studies.

The Role of Bisphosphonates Prior to Denosumab Treatment on Rebound Fractures: A Mini Review

Denosumab is a potent anti-resorptive medication used to treat patients at high risk for osteoporosis; however, its beneficial effects on the skeletal system are quickly reversed after discontinuation. In contrast, bisphosphonates (BPs) are anti-resorptive agents with residual effects on the bone matrix; thus, these are capable of preserving bone mass for a long time. Therefore, subsequent anti-resorptive treatment with BPs is mandatory to prevent rebound fractures. Furthermore, BP administration before denosumab treatment appears to be a reasonable strategy for reducing hyperactivation of bone remodeling. In this review, we summarize the effects of BP administration before denosumab treatment in preventing rebound fractures after denosumab discontinuation.

Rebound-associated vertebral fractures after denosumab discontinuation in a lung cancer patient with bone metastases

Denosumab is a commonly used antiresorptive treatment in patients with osteoporosis or solid tumours with bone metastases. Upon denosumab discontinuation, a rebound phenomenon can occur that results in an increased (vertebral) fracture risk. This phenomenon is well-known in the setting of osteoporosis but rarely reported in cancer patients with bone metastases discontinuing denosumab. We present the case of a 43-year old women with lung cancer and bone metastases who suffered multiple vertebral fractures after discontinuation of denosumab.

Multiple vertebral fractures after suspension of denosumab. A series of 56 cases

BACKGROUND

Denosumab is a monoclonal antibody approved for the treatment of postmenopausal osteoporosis. The withdrawal of denosumab produces an abrupt loss of bone mineral density and may cause multiple vertebral fractures (MVF).

OBJECTIVE

The objective of this study is to study the clinical, biochemical, and densitometric characteristics in a large series of postmenopausal women who suffered MVF after denosumab withdrawal. Likewise, we try to identify those factors related to the presence of a greater number of vertebral fractures (VF).

PATIENTS AND METHODS

Fifty-six patients (54 women) who suffered MVF after receiving denosumab at least for three consecutive years and abruptly suspended it. A clinical examination was carried out. Biochemical bone remodelling markers (BBRM) and bone densitometry at the lumbar spine and proximal femur were measured. VF were diagnosed by magnetic resonance imaging MRI, X-ray, or both at dorsal and lumbar spine.

RESULTS

Fifty-six patients presented a total of 192 VF. 41 patients (73.2%) had not previously suffered VF. After discontinuation of the drug, a statistically significant increase in the BBRM was observed. In the multivariate analysis, only the time that denosumab was previously received was associated with the presence of a greater number of VF (P = .04).

CONCLUSIONS

We present the series with the largest number of patients collected to date. 56 patients accumulated 192 new VF. After the suspension of denosumab and the production of MVF, there was an increase in the serum values of the BBRM. The time of denosumab use was the only parameter associated with a greater number of fractures.

Fractures After Denosumab Discontinuation: A Retrospective Study of 797 Cases

A rebound of osteoclast activity during the 2 years after a treatment or prevention of osteoporosis with denosumab (Dmab) leads to an increased risk of vertebral fractures (VFs). We attempted to identify the risk factors for these VF and to examine the protective role of bisphosphonates. For that, 22 specialists in Switzerland provided data of unselected patients, treated with denosumab for osteoporosis or breast cancer without metastases under aromatase inhibitors, who have received at least two injections of Dmab, with at least 1 year of follow-up after discontinuation. The questionnaire covered separately the periods before, during, and after Dmab treatment, and registered clinical, radiological, and lab data. For the analysis of the risk factors, the main outcomes were the time to the first VF after the treatment, the presence of multiple VFs (MVFs), and the number of VFs. The incidence of VF was 16.4% before, 2.2% during, and 10.3% after the treatment with Dmab. The risk of VF after Dmab discontinuation was associated with an increased risk of non-vertebral fractures. The pretreatment predictors of the post-treatment fracture risk were a parental hip fracture and previous VFs. Further risk factors appeared later, such as low total hip bone mineral density (BMD) during and after denosumab, increased bone resorption markers, and the loss of total hip BMD after the denosumab. Treatment with bisphosphonates, especially after Dmab, had a protective effect. Bisphosphonates given before Dmab did not further decrease the risk of VF in cases who got bisphosphonates after Dmab. This study shows that the risk of VF is poorly predictable before the prescription of denosumab. But during and after the treatment, bone resorption markers and BMD have a significant predictive value. Bisphosphonates after the treatment with denosumab are protective against VFs. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Zoledronic Acid after Treatment with Denosumab is Associated with Bone Loss within 1 Year

BACKGROUND

Bone mineral density (BMD) declines when zoledronic acid (ZA) is administered. This case series describes the patterns of change in BMD when 1 or 2 doses of ZA are administered after denosumab.

METHODS

Twelve patients who received at least 2 doses of denosumab followed by at least 1 dose of ZA and who had a dual energy X-ray absorptiometry (DXA) scan at the end of denosumab and 1 year after the first dose of ZA were included. We excluded patients with bone cancer or conditions affecting bone metabolism, including hyperparathyroidism, rickets, osteogenesis imperfecta, rheumatologic disorders, fibrous dysplasia, Paget's disease of bone, untreated hyperthyroidism, chronic kidney disease, liver cirrhosis, malabsorption, ongoing corticosteroid therapy, and aromatase inhibitor use.

RESULTS

There was a significant decline in BMD at the femoral neck within 1 year of the first ZA dose and a non-significant downward trend in the hip and lumbar spine. This trend was more severe in patients with osteoporosis at the time of drug transition. No increase in clinical vertebral fractures was observed. BMD seemed to stabilize in a smaller number of patients who received a second dose of ZA and had a DXA scan 1 year later.

CONCLUSIONS

A single dose of ZA administered approximately 6 months after denosumab leads to some BMD loss, mostly within 1 year of ZA administration, particularly in patients with osteoporosis at the time of denosumab discontinuation.

Denosumab Discontinuation and the Rebound Phenomenon: A Narrative Review

Denosumab is a potent antiresorptive agent that substantially increases bone mineral density and reduces fracture rates at all skeletal sites for as long as it is administered. However, its favorable skeletal effects reverse quickly upon its discontinuation, because of a vast increase of osteoclast number and activity, which leads to a subsequent profound increase of bone turnover above pre-treatment values, a phenomenon commonly described as “rebound phenomenon”. More importantly, most patients experience rapid, profound bone loss due to this burst of bone resorption that may lead in a minority of these patients to occurrence of fractures, especially multiple vertebral fractures. Therefore, subsequent antiresorptive treatment is mandatory, although the optimal regimen is yet to be clarified. In the present review, we outline what is currently known regarding the negative effects of denosumab discontinuation on different aspects of bone status, the factors that may affect them, and strategies to prevent them.

The Effect of Teriparatide for the Treatment of Multiple Spontaneous Clinical Vertebral Fractures after Discontinuation of Denosumab in a Female Patient with Rheumatoid Arthritis: A Case Report

Discontinuation of denosumab is associated with the risk of rebound in bone turnover and rebound-associated spontaneous clinical vertebral fractures. This case report presents an 86-year-old woman with rheumatoid arthritis who experienced rebound-associated spontaneous clinical vertebral fractures at 9 months after denosumab discontinuation. Following 5-year bisphosphonate treatment, the patient had 9 injections of 60-mg denosumab every 6 months. Because of tooth extraction, denosumab treatment was discontinued, and raloxifene was administered. At 9 months after the last denosumab injection, the patient experienced severe low back pain. Magnetic resonance imaging (MRI) and radiograph demonstrated clinical fracture at the fourth lumbar vertebra. MRI performed at 3 months after first fracture showed two additional fractures at the second and third lumbar vertebrae. Teriparatide was administered for management of rebound-associated spontaneous clinical, multiple vertebral fractures. Teriparatide was effective for accelerating the fracture healing and suppressing the occurrence of new fractures. However, 2-year treatment of teriparatide did not have suppressive effect of rebound in bone turnover and general bone loss. This case suggested that teriparatide was effective for suppression of new rebound-associated spontaneous clinical vertebral fractures, but not effective in prevention of general bone loss after denosumab discontinuation.

Zoledronic acid sequential therapy could avoid disadvantages due to the discontinuation of less than 3-year denosumab treatment

INTRODUCTION

Rapid descent in bone mineral density (BMD) and ascent in bone turnover marker (BTM) occur within the short period following denosumab (Dmab) discontinuation. In addition, the incidence of vertebral fracture also rises within the short period. The purpose of this study is to investigate the effects of sequential therapy using zoledronic acid (ZOL) on any adverse events after Dmab discontinuation.

MATERIALS AND METHODS

This study was a multicenter retrospective observational study, and the subjects were osteoporosis patients who visited our institutions between 2013 and 2018. We performed sequential therapy using ZOL for 30 patients who had difficulty continuing Dmab, due to physical or social reasons, and investigated the fracture incidence and BMD/BTM changes at 4 time points (at the start of Dmab, the start of ZOL, 6 months after ZOL and 12 months after ZOL).

RESULTS

No new vertebral/nonvertebral fractures were observed at each time point after switching from Dmab to ZOL in any of the 30 patients. The BMD/BTM changes were evaluated in 18 of the 30 cases, since all data of lumbar/femoral neck BMDs and TRACP-5b at 4 time points was only available in 18 cases. BMDs significantly increased at each time point compared with that at the start of Dmab. Serum TRACP-5b significantly decreased at each time point compared with that at the start of Dmab.

CONCLUSION

It was suggested that sequential therapy using ZOL could suppress the decrease of BMD, and increase of BTM, if the period of Dmab administration was less than 3 years.

Fracture risk and management of discontinuation of denosumab therapy: a systematic review and position statement by ECTS

CONTEXT

Denosumab discontinuation is characterized by an increase in bone turnover overriding pre-treatment status, a rapid bone loss in the majority and multiple vertebral fractures (VFx) in some patients.

METHODS

A working group of the European Calcified Tissue Society (ECTS) performed an updated systematic review of existing literature on changes of bone turnover, bone mineral density (BMD), and fracture risk after denosumab discontinuation and provided advice on management based on expert opinion.

RESULTS

Important risk factors for multiple VFx following denosumab cessation are prevalent VFx, longer duration off therapy, greater gain in hip BMD during therapy, and greater loss of hip BMD after therapy according to a retrospective analysis of the FREEDOM Extension Study. Case series indicate that prior bisphosphonate therapy mitigates the biochemical rebound phenomenon after denosumab discontinuation, but it is uncertain whether this attenuation prevents BMD loss and fractures. Current evidence indicates partial efficacy of subsequent antiresorptive treatment with results seemingly dependent on duration of denosumab treatment.

CONCLUSIONS

A careful assessment of indications to start denosumab treatment is advised, especially for younger patients. A case for long-term treatment with denosumab can be made for patients at high fracture risk already on denosumab treatment given the favorable efficacy and safety profile. In case of denosumab discontinuation, alternative antiresorptive treatment should be initiated 6 months after the final denosumab injection. Assessment of bone turnover markers may help define the optimal regimen, pending results of ongoing RCTs. Patients having sustained VFx should be offered prompt treatment to reduce high bone turnover.

Bone Health and Osteoporosis Prevention and Treatment

Postmenopausal osteoporosis is a common condition and is associated with increased risk of fracture, including hip and vertebral fractures that in turn can have devastating consequences on morbidity and mortality. In this article, we review the pathogenesis and diagnostic approach to postmenopausal osteoporosis. We review available nonpharmacologic and pharmacologic therapies and we discuss their clinical efficacy and complications, with a detailed discussion of atypical femur fractures and osteonecrosis of the jaw.

Long-term follow up after denosumab treatment for osteoporosis - rebound associated with hypercalcemia, parathyroid hyperplasia, severe bone mineral density loss, and multiple fractures: a case report

BACKGROUND

The rebound effect after stopping treatment with denosumab may be associated with rapid loss of the gains in bone mineral density achieved with treatment, high levels of bone remodeling markers, the occurrence of vertebral fractures, and even hypercalcemia.

CASE PRESENTATION

A 64-year-old osteoporotic Caucasian woman suffered from a fracture of her second lumbar vertebra in 2004. From January 2005, she was treated with denosumab for 9 years, with good densitometry results for her hip and lumbar areas, and no fractures over the last 6 years of treatment. Ten months after the treatment with denosumab was stopped, a cascade of vertebral fractures, including some in unusual locations (third thoracic vertebra), and multiple rib fractures in a context of hypercalcemia, suggested possible malignancy. A complete evaluation, including systemic, biological, and biopsy analyses, ruled out this hypothesis. The hypercalcemia was associated with normal plasma phosphate and vitamin D concentrations, and a high parathyroid hormone level, with an abnormal fixation of the lower lobe of the thyroid on sesta-methoxy-isobutyl-isonitrile scintigraphy. Histological analysis of the excised parathyroid tissue revealed hyperplasia. The associated thyroidectomy (goiter) led to the discovery of a thyroid papillary microcarcinoma.

CONCLUSIONS

We consider the consequences of this rebound effect, not only in terms of the major loss of bone density (return to basal values within 3 years) and the multiple disabling fracture episodes, but also in terms of the hypercalcemia observed in association with apparently autonomous tertiary hyperparathyroidism. Several cases of spontaneous reversion have been reported in children, but the intervention in our patient precluded any assessment of the possible natural course. The discovery of an associated thyroid neoplasm appears to be fortuitous. Better understanding of the various presentations of the rebound effect after stopping treatment with denosumab would improve diagnostic management of misleading forms, as in this case. Bisphosphonates could partially prevent this rebound effect.

Current and Emerging Therapeutic Options for the Management of Rare Skeletal Diseases

Increasing knowledge in the field of rare diseases has led to new therapeutic approaches in the last decade. Treatment strategies have been developed after elucidation of the underlying genetic alterations and pathophysiology of certain diseases (e.g., in osteogenesis imperfecta, achondroplasia, hypophosphatemic rickets, hypophosphatasia and fibrodysplasia ossificans progressiva). Most of the drugs developed are specifically designed agents interacting with the disease-specific cascade of enzymes and proteins involved. While some are approved (asfotase alfa, burosumab), others are currently being investigated in phase III trials (denosumab, vosoritide, palovarotene). To offer a multi-disciplinary therapeutic approach, it is recommended that patients with rare skeletal disorders are treated and monitored in highly specialized centers. This guarantees the greatest safety for the individual patient and offers the possibility of collecting data to further improve treatment strategies for these rare conditions. Additionally, new therapeutic options could be achieved through increased awareness, not only in the field of pediatrics but also in prenatal and obstetric specialties. Presenting new therapeutic options might influence families in their decision of whether or not to terminate a pregnancy with a child with a skeletal disease.