A Subtrochanteric Femoral Stress Fracture following Bisphosphonate Treatment in an Adolescent Girl

High doses of zoledronic acid induce differential effects on femur and jawbone microstructure

OBJECTIVES

The aim of this study is to investigate the long-term effects on jaw and femur bone induced by oncologic doses of zoledronic acid in a young rat model.

MATERIAL AND METHODS

Six 12-week-old male Wistar rats received zoledronic acid (0.6 mg/kg) and six control rats received saline solution in the same volume. Compounds were administered intraperitoneally in five doses every 28 days. Euthanasia was performed 150 days after therapy onset. After animal sacrifice, their mandibles and femurs were scanned ex vivo using a high-resolution (14 μm) micro-computed tomography. Morphometric bone parameters were calculated using CT-Analyzer (Bruker, Belgium) between the first and second mandibular molars and in the distal femur metaphysis and epiphysis.

RESULTS

The treatment group as compared to the controls showed a significantly (p < .05) increased bone quantity (↑BV/TV, ↓Po[Tot], ↑Tb.Th), bone density (↑TMD, ↑BMD), and osteosclerosis of the trabecular bone (↓Tb.Sp, ↓Conn.Dn, ↓Tb.Pf, ↓SMI) in all anatomical sites. Bone remodeling suppression due to zoledronic acid treatment was more pronounced (p < .05) in the femoral metaphysis relative to the mandible and epiphysis. The exploratory linear discriminant analysis showed that for the mandible, it was mainly the bone quantity-related morphometric indices (BV/TV and Tb.Th), while for the femoral epiphysis and metaphysis, it was bone structure-related (Tb.Pf and Tb.N), which are of primary importance to study the treatment effect.

CONCLUSION

High doses of bisphosphonates can differently affect the bone quantity, density, and structure in long bones and jawbones. In the metaphysis, bone changes were primarily concentrated in the region of the growth plate. Future studies may consider the use of bone morphometric indices to evaluate the effect of bisphosphonates.

Bisphosphonate use in children with cerebral palsy

BACKGROUND

Cerebral palsy (CP) is a heterogeneous group of non-progressive disorders of posture or movement, caused by a lesion of the developing brain. Osteoporosis is common in children with cerebral palsy, particularly in children with reduced gross motor function, and leads to an increased risk of fractures. Gross motor function in children with CP can be categorised using a tool called the Gross Motor Function Classification System (GMFCS). Bisphosphonate increases bone mineral density (BMD) and reduces fracture rates. Bisphosphonate is used widely in the treatment of adult osteoporosis. However, the use of bisphosphonate in children with CP remains controversial, due to a paucity of evidence and a lack of recent trials examining the efficacy and safety of bisphosphonate use in this population.

OBJECTIVES

To examine the efficacy and safety of bisphosphonate therapy in the treatment of low BMD or secondary osteoporosis (or both) in children with cerebral palsy (GMFCS Levels III to V) who are under 18 years of age.

SEARCH METHODS

In September 2020, we searched CENTRAL, MEDLINE, Embase, six other databases, and two trial registers for relevant studies. We also searched the reference lists of relevant systematic reviews, trials, and case studies identified by the search, and contacted the authors of relevant studies in an attempt to identify unpublished literature.

SELECTION CRITERIA

All relevant randomised controlled trials (RCTs), and quasi-RCTs, comparing at least one bisphosphonate (given at any dose, orally or intravenously) with placebo or no drug, for the treatment of low BMD or osteoporosis in children up to 18 years old, with cerebral palsy (GMFCS Levels III to V).

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. We were unable to conduct any meta-analyses due to insufficient data, and therefore provide a narrative assessment of the results.

MAIN RESULTS

We found two relevant RCTs (34 participants). Both studies included participants with non-ambulatory CP or CP and osteoporosis. Participants in both studies were similar in severity of CP, age distribution, and sex distribution. The two trials used different bisphosphonate medications and different intervention durations, but further comparison of the interventions was not possible due to a lack of published data from one trial. One trial received funding and support from research, academic, and hospital foundations, with pharmaceutical companies providing components of the calcium and vitamin supplement; the other trial did not report sources of funding. We judged one study at an overall high risk of bias; the other as overall unclear risk of bias.

PRIMARY OUTCOME

Compared to placebo or no treatment, both studies provided very low certainty evidence of improved BMD at least four months post-intervention in children treated with bisphosphonate. Only one study (12 participants) provided sufficient detail to assess a measure of the effect, and reported an improvement at six months post-intervention in lumbar spine z-score (mean difference (MD) 18%, 95% confidence interval (CI) 6.57 to 29.43; very low certainty evidence).

SECONDARY OUTCOMES

Very low certainty evidence from one study found that bisphosphonate reduced serum N-telopeptides (NTX) more than placebo; the other study reported that both bisphosphonate plus alfacalcidol and alfacalcidol alone reduced NTX, but did not compare groups. One study reported inconclusive results between groups for serum bone-specific alkaline phosphatase (BAP). The other study reported that both bisphosphonate plus alfacalcidol and alfacalcidol alone reduced BAP, but did not compare groups. Neither study reported data for the effect of bisphosphonate treatment on changes in volumetric BMD in the distal radius or tibia, changes in fracture frequency, bone pain, or quality of life. One study reported that two participants had febrile events noted during their first dosing schedule, but no further adverse events were reported in either relevant study.

AUTHORS' CONCLUSIONS

Based on the available evidence, there is very low certainty evidence that bisphosphonate treatment may improve bone health in children with cerebral palsy. We could only include one study with 14 participants in the assessment of the effect size; therefore, the precision of the effect estimate is low. We could only evaluate one planned primary outcome, as there was insufficient detail reported in the relevant studies. Further research from RCTs on the effect and safety of bisphosphonate to improve bone health in children with cerebral palsy is required. These studies should clarify the optimal standard treatment regarding weight-bearing exercises, vitamin D and calcium supplementation, and should include fracture frequency as a primary outcome.

Intravenous bisphosphonate therapy in children with spinal muscular atrophy

This is the first report on safety and efficacy of intravenous bisphosphonates (IV BP) for treatment of disuse osteoporosis and low bone mineral density (BMD) in children with spinal muscular atrophy (SMA). IV BP appears to be safe and effective in fracture rate reduction. However, caution is necessary given the occurrence of an atypical femur fracture.

INTRODUCTION

Children with SMA are at high risk for fragility fractures and low BMD. IV BP have been used for treatment of disuse osteoporosis in pediatrics. However, safety and efficacy of IV BP in the SMA population has not been reported.

METHODS

Retrospective chart review of IV BP for treatment of disuse osteoporosis and low BMD in children with SMA at a tertiary pediatric center from 2010 to 2018 RESULTS: Eight patients (50% female; 75% SMA type 1; median age at first infusion 6.7 years) receiving a total of 39 infusions (54% pamidronate, 46% zoledronic acid) were included in this report. Acute phase reactions occurred following 38% and 3% of initial and subsequent infusions, respectively. BMD trended toward improvement at 1 year post-treatment. Among six patients who had > 2 years of follow-up, fracture rate decreased from 1.4 to 0.1 fracture/year. An atypical femur fracture was observed in one patient.

CONCLUSION

These findings suggest that in children with SMA, IV BP therapy appears to be safe with minimal acute side effects and effective to reduce fracture rate. Caution is still needed given the occurrence of an atypical femur fracture in SMA population.

Consensus guidelines on the use of bisphosphonate therapy in children and adolescents

Bisphosphonate therapy is the mainstay of pharmacological intervention in young people with skeletal fragility. The evidence of its use in a variety of conditions remains limited despite over three decades of clinical experience. On behalf of the Australasian Paediatric Endocrine Group, this evidence-based consensus guideline presents recommendations and discusses the graded evidence (using the GRADE system) for these recommendations. Primary bone fragility disorders such as osteogenesis imperfecta are considered separately from osteoporosis secondary to other clinical conditions (such as cerebral palsy, Duchenne muscular dystrophy). The use of bisphosphonates in non-fragility conditions, such as fibrous dysplasia, avascular necrosis, bone cysts and hypercalcaemia, is also discussed. While these guidelines provide an evidence-based approach where possible, further research is required in all clinical applications in order to strengthen the recommendations made.

Osteonecrosis of the Jaw and Rebound Hypercalcemia in Young People Treated With Denosumab for Giant Cell Tumor of Bone

CONTEXT

Denosumab, an inhibitor of receptor activator of nuclear factor κ-B ligand, is an approved treatment of giant cell tumor of bone (GCTB) in adults and "skeletally mature" adolescents. Safety concerns include oversuppression of bone remodelling, with risk of osteonecrosis of the jaw (ONJ) and atypical femur fractures during treatment in adults and rebound hypercalcemia after treatment cessation in children. To date, ONJ has never been reported in children or adolescents.

OBJECTIVES

To describe serious adverse effects during and following high-dose denosumab therapy in GCTB patients.

PATIENTS

Two adolescents (14 and 15 years) and a young adult (40 years) received fixed-dose denosumab for GCTB for 1.3 to 4 years (cumulative dose, 47 to 98 mg/kg), which was stopped because of development of ONJ in one adolescent and bilateral femoral cortical stress reactions in the young adult. All three patients developed rebound hypercalcemia with acute kidney injury 5.5 to 7 months after denosumab cessation.

RESULTS

The ONJ necessitated surgical debridement. Rebound hypercalcemia (serum calcium, 3.1 to 4.3 mmol/L) was unresponsive to hyperhydration alone, requiring repeated doses of calcitonin or intravenous bisphosphonate treatment. Hypercalcemia recurred in two patients within 4 weeks, with normal serum calcium profiles thereafter. All patients were naive to chemotherapy, radiotherapy, bisphosphonates, and corticosteroids and were metastases free, confirming the causative role of denosumab in these complications.

CONCLUSION

These suppression-release effects of high-dose denosumab on bone remodeling raise questions about safety of fixed dosing and treatment duration. In young people, weight-adjusted dosing and safety monitoring during and after antiresorptive therapy is required.

Bisphosphonate Withdrawal: Effects on Bone Formation and Bone Resorption in Maturing Male Mice

Bisphosphonates are being increasingly used to treat pediatric patients with skeletal disorders. However, the effects of long-term bisphosphonate therapy and cessation of therapy during growth are unclear. Thus, studies were undertaken to determine the effects of alendronate discontinuation after treatment of C57Bl/6 mice during the period of rapid skeletal growth. Compared with vehicle-treated mice, 16 weeks of alendronate treatment starting at age 18 days resulted in a 3.7-fold increase in trabecular bone in the setting of suppressed bone formation. Alendronate therapy for 8 weeks followed by 8 weeks of vehicle treatment resulted in a more pronounced increase in trabecular bone compared with mice treated with alendronate for 16 weeks (1.7-fold) and to vehicle-treated controls (6.5-fold). Mice that received alendronate for 8 weeks followed by 8 weeks of vehicle exhibited increased osteoblast surface (2.5-fold), mineralizing surface (5.7-fold), and bone formation rate (5.1-fold) compared with mice treated continuously with alendronate. However, these parameters were not restored to the levels observed in the vehicle-treated mice. Thus, partial resumption of bone formation upon cessation of bisphosphonate therapy leads to a greater increase in trabecular bone than that found when bisphosphonates are administered continuously to growing mice. These data suggest that intermittent administration of bisphosphonates may optimize their beneficial effects on the growing skeleton. © 2017 American Society for Bone and Mineral Research.