Bisphosphonate use in children with bone disease

Drug-induced osteopetrosis

Osteopetrosis (OPT) denotes the consequences from failure of osteoclasts to resorb bone and chondroclasts to remove calcified physeal cartilage throughout growth. Resulting impairment of skeletal modeling, remodeling, and growth compromises widening of medullary spaces, formation of the skull, and expansion of cranial foramina. Thus, myelophthisic anemia, raised intracranial pressure, and cranial nerve palsies complicate OPT when severe. Osteopetrotic bones fracture due to misshaping, failure of remodeling to weave the collagenous matrix of cortical osteons and trabeculae, persistence of mineralized growth plate cartilage, "hardening" of hydroxyapatite crystals, and delayed healing of skeletal microcracks. Teeth may fail to erupt. Now it is widely appreciated that OPT is caused by germline loss-of-function mutation(s) usually of genes involved in osteoclast function, but especially rarely of genes necessary for osteoclast formation. Additionally, however, in 2003 we published a case report demonstrating that prolonged excessive dosing during childhood of the antiresorptive aminobisphosphonate pamidronate can sufficiently block osteoclast and chondroclast activity to recapitulate the skeletal features of OPT. Herein, we include further evidence of drug-induced OPT by illustrating osteopetrotic skeletal changes from repeated administration of high doses of the aminobisphosphonate zoledronic acid (zoledronate) given to children with osteogenesis imperfecta.

Percutaneous screw fixation of fractured neck of femur in a teenage girl with osteogenesis imperfecta. A case report

INTRODUCTION

Neck of femur fracture in osteogenesis imperfecta is rarely reported. The management is uncertain and always reported as difficult. Clinical outcomes are not well described.

CASE PRESENTATION

A teenage girl, who is known to have osteogenesis imperfecta, sustained neck of femur fracture in the presence of a previously inserted implant. She was treated by percutaneous screw fixation. In both immediate and long term follow up, our patient had satisfactory outcome and return to pre-fracture functional status.

DISCUSSION

Dealing with fragility fracture in small abnormal hips is challenging especially, in the presence of a retained implant in- situ. Intra-operative difficulty were encountered during positioning, reduction, and screw insertion attempt.

CONCLUSION

This rare case illustrates the anticipated difficulties in managing neck of femur fracture in osteogenesis imperfect patients. It also emphasize on the importance of surgical fixation to control pain and allow for healing in anatomically functional position.

Fracture of mandible during yawning in a patient with osteogenesis imperfecta

Osteogenesis imperfecta is a genetic disorder characterised by fragility and multiple fractures of bones. Clinical signs and symptoms vary depending on the type of disease. Fractures of facial bones are rare compared with load-bearing long bones. We report a case of fracture of the mandible during yawning which was managed by open reduction and internal fixation.

The use of bisphosphonates in children: review of the literature and guidelines for dental management

Bisphosphonates are inhibitors of osteoclastic bone resorption with therapeutic benefit in a variety of bone disorders in both adults and children. While these agents have been routinely used in adults for the past three decades, their more recent introduction into paediatric medicine means there is a paucity of data on long-term safety and effects on dental development. There is uncertainty regarding the dental management of children treated with bisphosphonates, particularly when invasive dental procedures, such as extractions and oral surgical procedures, are required. There are limited data with which to make recommendations about the dental management of patients treated with bisphosphonates, and there are no published recommendations that specifically address paediatric patients. This paper aims to outline paediatric uses and adverse effects of bisphosphonates and present recommendations on the dental management of children receiving bisphosphonates.

Near-infrared fluorescent probe traces bisphosphonate delivery and retention in vivo

Bisphosphonate use has expanded beyond traditional applications to include treatment of a variety of low-bone-mass conditions. Complications associated with long-term bisphosphonate treatment have been noted, generating a critical need for information describing the local bisphosphonate-cell interactions responsible for these observations. This study demonstrates that a fluorescent bisphosphonate analogue, far-red fluorescent pamidronate (FRFP), is an accurate biomarker of bisphosphonate deposition and retention in vivo and can be used to monitor site-specific local drug concentration. In vitro, FRFP is competitively inhibited from the surface of homogenized rat cortical bone by traditional bisphosphonates. In vivo, FRFP delivery to the skeleton is rapid, with fluorescence linearly correlated with bone surface area. Limb fluorescence increases linearly with injected dose of FRFP; injected FRFP does not interfere with binding of standard bisphosphonates at the doses used in this study. Long-term FRFP retention studies demonstrated that FRFP fluorescence decreases in conditions of normal bone turnover, whereas fluorescence was retained in conditions of reduced bone turnover, demonstrating preservation of local FRFP concentration. In the mandible, FRFP localized to the alveolar bone and bone surrounding the periodontal ligament and molar roots, consistent with findings of osteonecrosis of the jaw. These findings support a role for FRFP as an effective in vivo marker for bisphosphonate site-specific deposition, turnover, and long-term retention in the skeleton.

Cyclic pamidronate therapy in children with osteogenesis imperfecta

BACKGROUND

Severe osteogenesis imperfecta (OI) is a disorder characterized by osteopenia, frequent fractures, progressive deformity, loss of mobility, and chronic bone pain. There has been no effective therapy for the disorder until recently. The main objective of this study was to determine the efficacy and safety of pamidronate in improving bone mineralization and reducing fracture incidence in osteogenesis imperfecta.

METHODS

Intravenous pamidronate was administered to 64 children (from 21 months to 10 years old) with severe OI, in a 1 mg/kg single daily dose for 3 sequential days at 4-month intervals, over 24-48 months duration. Clinical status, biochemical characteristics including bone turnover markers, bone mineral density of the lumbar spine and femoral neck, and radiological changes were assessed regularly during treatment.

RESULTS

The number of fractures decreased from a median of 8 (range 4-11) to 0 fractures/year (range 0-4) (p <0.05). After 16 months of treatment, there was significant improvement in bone mineral density (BMD-DEXA) z-score of the lumbar spine from a median of -5.90 (range -7.01 to -4.76) to -2.70 (range -4.46 to -1.98) (p <0.001). Serum alkaline phosphatase (ALP) (bone formation marker) decreased from a median of 731.0 U/l (range 438-998 U/l) to 183 U/l (range 95-286 U/l) (p <0.001), implying a significant reduction in bone turnover and resorption and increase in bone mineralization. There was no improvement in growth velocity or height SDS. Mobility and ambulation improved in all but five children (all five had taken the drug for less than 2.5 years). There was a significant relief of chronic pain and fatigue but no adverse effects in all children using the drug.

CONCLUSION

Cyclic pamidronate administration is effective in improving bone mineralization and reducing fracture incidence in childhood osteogenesis imperfecta.

Bisphosphonate-induced osteopetrosis: novel bone modeling defects, metaphyseal osteopenia, and osteosclerosis fractures after drug exposure ceases

In 2003, we reported on a 12-yr-old boy who had developed osteopetrosis (OPT) while receiving pamidronate (PMD) for idiopathic bone pain and enigmatic elevation in circulating bone alkaline phosphatase. Now 17 yr of age, he was re-evaluated 6.5 yr after PMD exposure stopped. Our patient described less bone pain but further limb fractures. His growth plates were fused, yet hyperphosphatasemia persisted. Radiographs documented interval fractures of a metacarpal, an osteosclerotic distal radius, and a dense diaphyseal segment of an ulna where a "chalkstick" break remained incompletely healed after 2 yr. There was new L(4) spondylolysis, and previous L(5) spondylolysis had caused spondylolisthesis. Modeling disturbances of OPT persisted, but partial recovery was shown by metaphyseal surfaces with a unique concave shape. Metaphyseal osteosclerosis had remodeled imperfectly to become focal areas of dense, diaphyseal bone. Newer metaphyseal bone was unexpectedly osteopenic, especially in his distal femurs where cortices were thin and a paucity of trabeculae was documented by CT. Femoral necks had become short and wide with an abnormal contour. A "bone-within-bone" configuration was now present throughout his skeleton. In vertebrae, endplates were thin, and trabecular osteopenia was present central and peripheral to the bands of osteosclerosis. BMD Z-scores assessed by DXA had decreased into the normal range in his spine, hip, and whole body. Iliac crest biopsy showed active bone formation, with much less accumulated primary spongiosa than during the PMD infusions. Osteoclasts that had been dysmorphic, round cells without polarization and off of bone surfaces were now unremarkable in number, location, and appearance. In conclusion, bisphosphonate toxicity during childhood can impair skeletal modeling and remodeling with structural changes that evolve and carry into adult life.

Osteogenesis imperfecta: diagnosis and treatment

Osteogenesis imperfecta is a heritable disorder characterized by extremely fragile bones, blue sclerae, dentinogenesis imperfecta, hearing loss, and scoliosis. In 1979, Sillence classified the condition into four types based on genetic and clinical criteria. Three more classifications have subsequently been added. Diagnosis of osteogenesis imperfecta may be done prenatally (in severe cases), clinically, radiographically, or via biochemical or genetic examination. Medical treatment consists of bisphosphonate use, even in patients younger than age 2 years. Surgical treatment consists of internal splinting of long bones. Research is currently being done on the use of smart intramedullary rods (ie, composed of nitinol shape-memory alloy) for correction of bone deformity and on the use of bone marrow transplantation to increase osteoblast density, thereby reducing fracture frequency.