Insights into bone health in Duchenne muscular dystrophy

Evaluation of bone health in terms of osteoporosis in adult patients with neuromuscular disease

Background/aim

There are no current guidelines to help clinicians decide whether patients with adult neuromuscular disease (NMD) should be screened or treated for osteoporosis (OP). This study was undertaken to investigate the presence of OP in patients with various types of NMD and to examine the relationship between OP evaluation parameters and functional status, daily living activities, balance, and ambulation levels.

Materials and methods

This cross-sectional study included 45 patients with NMDs. The patients were divided into 3 groups, depending on the affected component of the motor unit (neuronopathy group, neuropathy group, and myopathy group). The laboratory and demographic data were recorded from patient files. Functional level, pain, muscular strength, balance, and daily living activity scores were evaluated. The presence of OP was quantified using bone densitometry, fracture history, and biochemical parameters. Clinical findings were correlated with laboratory and dual-energy X-ray absorptiometry (DEXA) findings.

Results

The mean hip T-score was -1.20, and the mean lumbar spine (L1-L4) T-score was -0.95 in all groups. Six patients with T-score values of -2.5 or below were detected. Vitamin D level was found to be low in all patient groups, especially in the myopathy group, but there was no significant difference (p > 0.05). There was a negative correlation between hip T-score and the frequency of falling (r = -0.604, p = 0.022), while a positive correlation was found between hip T-score and the age at which independent walking was no longer possible (r = 0.900, p = 0.037).

Conclusion

OP is often overlooked in NMD patients with neurological problems and a high risk of falling. These patients should be screened for bone health and fragility.

Reduced bone mineral density in adolescents with Duchenne Muscular Dystrophy (DMD) and scoliosis

Duchenne muscular dystrophy is a progressive disease usually associated with loss of ambulation and progressive scoliosis. Immobilisation and glucocorticoid treatment are predisposing factors for reduced bone mineral density (BMD). Analysis of quantitative computed tomography revealed low BMD in thoracic and lumbar vertebrae in comparison to age- and sex-matched healthy controls.

INTRODUCTION

Evaluation of vertebral bone mineral density (BMD) in Duchenne Muscular Dystrophy (DMD) adolescents with untreated advanced scoliosis and comparison with the BMD values of healthy age-matched controls, based on quantitative computer tomography.

METHODS

Thirty-seven DMD adolescents (age 15.6 ± 2.5 years) with spinal deformity were evaluated clinically and radiologically prior to definite spinal fusion and compared to 31 male and age-matched healthy individuals (age 15.7 ± 2.3 years). Data related to previous medical treatment, physiotherapy and ambulatory status was also analysed. Scoliotic curves were measured on plain sitting radiographs of the spine. The BMD Z-scores of the thoracic and lumbar vertebrae were calculated with QCTpro® (Mindways Software Inc., USA), based on data sets of preoperative, phantom pre-calibrated spinal computed tomography scans.

RESULTS

A statistically significant lower BMD could be found in DMD adolescents, when compared to healthy controls, showing an average value for the lumbar spine of 80.5 ± 30.5 mg/cm³. Z-scores deteriorated from the upper thoracic towards the lower lumbar vertebrae. All but the uppermost thoracic vertebrae had reduced BMD values, with the thoracolumbar and lumbar region demonstrating the lowest BMD. No significant correlation was observed between BMD and the severity of the scoliotic curve, previous glucocorticoid treatment, cardiovascular impairment, vitamin D supplementation, non-invasive ventilation or physiotherapy.

CONCLUSION

DMD adolescents with scoliosis have strongly reduced BMD Z-scores, especially in the lumbar spine in comparison to healthy controls. These findings support the implementation of a standardised screening and treatment protocol. Level of evidence/clinical relevance: therapeutic level III.

Anabolic actions of PTH in murine models: two decades of insights

Parathyroid hormone (PTH) is produced by the parathyroid glands in response to low serum calcium concentrations where it targets bones, kidneys, and indirectly, intestines. The N-terminus of PTH has been investigated for decades for its ability to stimulate bone formation when administered intermittently (iPTH) and is used clinically as an effective anabolic agent for the treatment of osteoporosis. Despite great interest in iPTH and its clinical use, the mechanisms of PTH action remain complicated and not fully defined. More than 70 gene targets in more than 90 murine models have been utilized to better understand PTH anabolic actions. Because murine studies utilized wild-type mice as positive controls, a variety of variables were analyzed to better understand the optimal conditions under which iPTH functions. The greatest responses to iPTH were in male mice, with treatment starting later than 12 weeks of age, a treatment duration lasting 5-6 weeks, and a PTH dose of 30-60 μg/kg/day. This comprehensive study also evaluated these genetic models relative to the bone formative actions with a primary focus on the trabecular compartment revealing trends in critical genes and gene families relevant for PTH anabolic actions. The summation of these data revealed the gene deletions with the greatest increase in trabecular bone volume in response to iPTH. These included PTH and 1-α-hydroxylase (Pth;1α(OH)ase, 62-fold), amphiregulin (Areg, 15.8-fold), and PTH related protein (Pthrp, 10.2-fold). The deletions with the greatest inhibition of the anabolic response include deletions of: proteoglycan 4 (Prg4, -9.7-fold), low-density lipoprotein receptor-related protein 6 (Lrp6, 1.3-fold), and low-density lipoprotein receptor-related protein 5 (Lrp5, -1.0-fold). Anabolic actions of iPTH were broadly affected via multiple and diverse genes. This data provides critical insight for future research and development, as well as application to human therapeutics. © 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).

Complexity of skeletal muscle degeneration: multi-systems pathophysiology and organ crosstalk in dystrophinopathy

Duchenne muscular dystrophy is a highly progressive muscle wasting disorder due to primary abnormalities in one of the largest genes in the human genome, the DMD gene, which encodes various tissue-specific isoforms of the protein dystrophin. Although dystrophinopathies are classified as primary neuromuscular disorders, the body-wide abnormalities that are associated with this disorder and the occurrence of organ crosstalk suggest that a multi-systems pathophysiological view should be taken for a better overall understanding of the complex aetiology of X-linked muscular dystrophy. This article reviews the molecular and cellular effects of deficiency in dystrophin isoforms in relation to voluntary striated muscles, the cardio-respiratory system, the kidney, the liver, the gastrointestinal tract, the nervous system and the immune system. Based on the establishment of comprehensive biomarker signatures of X-linked muscular dystrophy using large-scale screening of both patient specimens and genetic animal models, this article also discusses the potential usefulness of novel disease markers for more inclusive approaches to differential diagnosis, prognosis and therapy monitoring that also take into account multi-systems aspects of dystrophinopathy. Current therapeutic approaches to combat muscular dystrophy are summarised.

Therapeutic aspects of cell signaling and communication in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a devastating chromosome X-linked disease that manifests predominantly in progressive skeletal muscle wasting and dysfunctions in the heart and diaphragm. Approximately 1/5000 boys and 1/50,000,000 girls suffer from DMD, and to date, the disease is incurable and leads to premature death. This phenotypic severity is due to mutations in the DMD gene, which result in the absence of functional dystrophin protein. Initially, dystrophin was thought to be a force transducer; however, it is now considered an essential component of the dystrophin-associated protein complex (DAPC), viewed as a multicomponent mechanical scaffold and a signal transduction hub. Modulating signal pathway activation or gene expression through epigenetic modifications has emerged at the forefront of therapeutic approaches as either an adjunct or stand-alone strategy. In this review, we propose a broader perspective by considering DMD to be a disease that affects myofibers and muscle stem (satellite) cells, as well as a disorder in which abrogated communication between different cell types occurs. We believe that by taking this systemic view, we can achieve safe and holistic treatments that can restore correct signal transmission and gene expression in diseased DMD tissues.

Bone Geometry Is Altered by Follistatin-Induced Muscle Growth in Young Adult Male Mice

The development of the musculoskeletal system and its maintenance depends on the reciprocal relationship between muscle and bone. The size of skeletal muscles and the forces generated during muscle contraction are potent sources of mechanical stress on the developing skeleton, and they shape bone structure during growth. This is particularly evident in hypermuscular global myostatin (Mstn)‐null mice, where larger muscles during development increase bone mass and alter bone shape. However, whether muscle hypertrophy can similarly influence the shape of bones after the embryonic and prepubertal period is unknown. To address this issue, bone structure was assessed after inducing muscle hypertrophy in the lower hindlimbs of young‐adult C57BL/6J male mice by administering intramuscular injections of recombinant adeno‐associated viral vectors expressing follistatin (FST), a potent antagonist of Mstn. Two FST isoforms were used: the full‐length 315 amino acid isoform (FST‐315) and a truncated 288 amino acid isoform (FST‐288). In both FST‐treated cohorts, muscle hypertrophy was observed, and the anterior crest of the tibia, adjacent to the tibialis anterior muscle, was lengthened. Hypertrophy of the muscles surrounding the tibia caused the adjacent cortical shell to recede inward toward the central axis: an event driven by bone resorption adjacent to the hypertrophic muscle. The findings reveal that inducing muscle hypertrophy in mice can confer changes in bone shape in early adulthood. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Aberrant RhoA activation in macrophages increases senescence-associated secretory phenotypes and ectopic calcification in muscular dystrophic mice

Duchenne Muscular Dystrophy (DMD) patients often suffer from both muscle wasting and osteoporosis. Our previous studies have revealed reduced regeneration potential in skeletal muscle and bone, concomitant with ectopic calcification of soft tissues in double knockout (dKO, dystrophin-/-; utrophin-/-) mice, a severe murine model for DMD. We found significant involvement of RhoA/ROCK (Rho-Associated Protein Kinase) signaling in mediating ectopic calcification of muscles in dKO mice. However, the cellular identity of these RhoA+ cells, and the role that RhoA plays in the chronic inflammation-associated pathologies has not been elucidated. Here, we report that CD68+ macrophages are highly prevalent at the sites of ectopic calcification of dKO mice, and that these macrophages highly express RhoA. Macrophages from dKO mice feature a shift towards a more pro-inflammatory M1 polarization and an increased expression of various senescence-associated secretory phenotype (SASP) factors that was reduced with the RhoA/ROCK inhibitor Y-27632. Further, systemic inhibition of RhoA activity in dKO mice led to reduced number of RhoA+/CD68+ cells, as well as a reduction in fibrosis and ectopic calcification. Together, these data revealed that RhoA signaling may be a key regulator of imbalanced mineralization in the dystrophic musculoskeletal system and consequently a therapeutic target for the treatment of DMD or other related muscle dystrophies.

Increased Expression of FGF-21 Negatively Affects Bone Homeostasis in Dystrophin/Utrophin Double Knockout Mice

Duchenne muscular dystrophy (DMD) is the most common muscular dystrophy seen in children. In addition to skeletal muscle, DMD also has a significant impact on bone. The pathogenesis of bone abnormalities in DMD is still unknown. Recently, we have identified a novel bone-regulating cytokine, fibroblast growth factor-21 (FGF-21), which is dramatically upregulated in skeletal muscles from DMD animal models. We hypothesize that muscle-derived FGF-21 negatively affects bone homeostasis in DMD. Dystrophin/utrophin double-knockout (dKO) mice were used in this study. We found that the levels of circulating FGF-21 were significantly higher in dKO mice than in age-matched WT controls. Further tests on FGF-21 expressing tissues revealed that both FGF-21 mRNA and protein expression were dramatically upregulated in dystrophic skeletal muscles, whereas FGF-21 mRNA expression was downregulated in liver and white adipose tissue (WAT) compared to WT controls. Neutralization of circulating FGF-21 by i.p. injection of anti-FGF-21 antibody significantly alleviated progressive bone loss in weight-bearing (vertebra, femur, and tibia) and non-weight bearing bones (parietal bones) in dKO mice. We also found that FGF-21 directly promoted RANKL-induced osteoclastogenesis from bone marrow macrophages (BMMs), as well as promoted adipogenesis while concomitantly inhibiting osteogenesis of bone marrow mesenchymal stem cells (BMMSCs). Furthermore, fibroblast growth factor receptors (FGFRs) and co-receptor β-klotho (KLB) were expressed in bone cells (BMM-derived osteoclasts and BMMSCs) and bone tissues. KLB knockdown by small interfering RNAs (siRNAs) significantly inhibited the effects of FGF21 on osteoclast formation of BMMs and on adipogenic differentiation of BMMSCs, indicating that FGF-21 may directly affect dystrophic bone via the FGFRs-β-klotho complex. In conclusion, this study shows that dystrophic skeletal muscles express and secrete significant levels of FGF-21, which negatively regulates bone homeostasis and represents an important pathological factor for the development of bone abnormalities in DMD. The current study highlights the importance of muscle/bone cross-talk via muscle-derived factors (myokines) in the pathogenesis of bone abnormalities in DMD. © 2019 American Society for Bone and Mineral Research.

Real-world outcomes of long-term prednisone and deflazacort use in patients with Duchenne muscular dystrophy: experience at a single, large care center

Aim: To assess outcomes among patients with Duchenne muscular dystrophy receiving deflazacort or prednisone in real-world practice. Methods: Clinical data for 435 boys with Duchenne muscular dystrophy from Cincinnati Children’s Hospital Medical Center were studied retrospectively using time-to-event and regression analyses. Results: Median ages at loss of ambulation were 15.6 and 13.5 years among deflazacort- and prednisone-initiated patients, respectively. Deflazacort was also associated with a lower risk of scoliosis and better ambulatory function, greater % lean body mass, shorter stature and lower weight, after adjusting for age and steroid duration. No differences were observed in whole body bone mineral density or left ventricular ejection fraction. Conclusion: This single center study adds to the real-world evidence associating deflazacort with improved clinical outcomes.

The role of delayed bone age in the evaluation of stature and bone health in glucocorticoid treated patients with Duchenne muscular dystrophy

Background

Low bone mineral density and an increased risk of appendicular and vertebral fractures are well-established consequences of Duchenne muscular dystrophy (DMD) and the risk of fractures is exacerbated by long-term glucocorticoid treatment. Monitoring of endocrine and skeletal health and timely intervention in at-risk patients is important in the management of children with DMD.

Methods

As part of the Norwegian Duchenne muscular dystrophy cohort study, we examined the skeletal maturation of 62 boys less than 18 years old, both currently glucocorticoid treated (n = 44), previously treated (n = 6) and naïve (n = 12). The relationship between bone age, height and bone mineral density (BMD) Z-scores was explored.

Results

The participants in the glucocorticoid treated group were short in stature and puberty was delayed. Bone age was significantly delayed, and the delay increased with age and duration of treatment. The difference in height between glucocorticoid treated and naïve boys was no longer significant when height was corrected for delayed skeletal maturation. Mean BMD Z-scores fell below − 2 before 12 years of age in the glucocorticoid treated group, with scores significantly correlated with age, duration of treatment and pubertal development. When BMD Z-scores were corrected for by retarded bone age, the increase in BMD Z-scores was significant for all age groups.

Conclusion

Our results suggest that skeletal maturation should be assessed in the evaluation of short stature and bone health in GC treated boys with DMD, as failing to consider delayed bone age leads to underestimation of BMD Z-scores and potentially overestimation of fracture risk.

The relationship of bone mineral density and vitamin D levels with steroid use and ambulation in patients with Duchenne muscular dystrophy

Objectives

This study aims to assess the bone mineral density (BMD) and serum levels of 25(OH)-vitamin D and their relationship with steroid use and ambulation in patients with Duchenne muscular dystrophy (DMD).

Patients and methods

Between January 2017 and May 2018, medical records of a total of 67 male patients (mean age, 13.9±4.3 years; range, 8 to 25 years) who were diagnosed with definite DMD were retrospectively analyzed. Demographic data, functional activity level, steroid use, fracture history and location, serum levels vitamin D, and lumbar and hip Z-scores in BMD at the time of the initial admission were recorded.

Results

The mean level of vitamin D was 13.4±7.5 ng/mL. In terms of serum levels of vitamin D, 28 patients (41.8%) had severe deficiency, 31 (46.3%) had insufficiency, and five patients (7.5%) had deficiency. Only three (4.5%) of the patients had sufficient levels of vitamin D. The hip Z-scores were significantly lower than lumbar Z scores. There was no significant difference in the lumbar and hip BMD measurements between the patients with and without steroid use. Lumbar Z-scores were significantly lower in non-ambulatory patients than ambulatory patients.

Conclusion

It is of utmost importance to evaluate the initial serum vitamin D levels in terms of bone health and prescribe replacement in case of deficiency/insufficiency in DMD patients. Since the decrease in the BMD is evident in this patient population, maintaining the mobilization as long as possible, providing loading on the bone for a long time, may be beneficial.

Pre-treatment with Pamidronate Improves Bone Mechanical Properties in Mdx Mice Treated with Glucocorticoids

Duchenne muscular dystrophy (DMD) is an X-linked disease of progressive muscle deterioration and weakness. Patients with DMD have poor bone health which is partly due to treatment with glucocorticoids, a standard therapy to prolong muscle function that also induces bone loss. Bisphosphonates are used to treat adults at risk of glucocorticoid-induced osteoporosis but are not currently used in DMD patients until after they sustain fractures. In this study, C57BL/10ScSn-mdx mice, a commonly used DMD animal model, received continuous glucocorticoid, prednisone treatment (0.083 mg/day) from 5 to 10 weeks of age. Pre-treatment with the bisphosphonate pamidronate started at 4 weeks of age over a period of 2 weeks or 6 weeks (cumulative dose 8 mg/kg for both) to assess the effectiveness of the two dosing regimens in ameliorating glucocorticoid-induced bone loss. Mdx mice treated with prednisone had improved muscle function that was not changed by pamidronate treatment. Glucocorticoid treatment caused cortical bone loss and decreased cortical bone strength. Both 2 and 6 week pamidronate treatment increased cortical thickness and bone area compared to prednisone-treated Mdx mice, however, only 2 week pamidronate treatment improved the strength of cortical bone compared to that of glucocorticoid-treated Mdx mice. In the trabecular bone, both pamidronate treatments significantly increased the amount of bone, and increased the ultimate load but not the energy to fail. These results highlight the importance of when and how much bisphosphonate is administered prior to glucocorticoid exposure.

Altered bone-regulating myokine expression in skeletal muscle Of Duchenne muscular dystrophy mouse models

INTRODUCTION

Duchenne muscular dystrophy (DMD) has been well characterized as a disease that affects both skeletal muscle and bone. The pathophysiology responsible for the deficits in bone tissue is still unclear.

METHODS

Quantitative reverse-transcription polymerase chain reaction and Western blot analyses of known myokines from skeletal muscle were performed on dystrophic mouse models and wild-type (WT) controls to identify differentially expressed bone-regulating myokines.

RESULTS

Twenty-four of 43 myokine genes demonstrated significantly different mRNA expression in the skeletal muscles of dystrophic mice when compared with muscles of WT mice. Several differently expressed bone-regulating myokine genes were identified, and their protein levels were also verified by Western blot.

CONCLUSIONS

Dystrophic skeletal muscle demonstrated a significantly altered myokine gene expression profile. mRNA and protein levels of several bone-regulating myokines were significantly altered in dystrophic skeletal muscle, which suggests pathological role of bone-regulating myokines on bone homeostasis in DMD. Muscle Nerve 58: 573-582, 2018.

An Overview of Recent Therapeutics Advances for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is the most common form of muscular dystrophy in childhood. Mutations of the DMD gene destabilize the dystrophin associated glycoprotein complex in the sarcolemma. Ongoing mechanical stress leads to unregulated influx of calcium ions into the sarcoplasm, with activation of proteases, release of proinflammatory cytokines, and mitochondrial dysfunction. Cumulative damage and reparative failure leads to progressive muscle necrosis, fibrosis, and fatty replacement. Although there is presently no cure for DMD, scientific advances have led to many potential disease-modifying treatments, including dystrophin replacement therapies, upregulation of compensatory proteins, anti-inflammatory agents, and other cellular targets. Recently approved therapies include ataluren for stop codon read-through and eteplirsen for exon 51 skipping of eligible individuals. The purpose of this chapter is to summarize the clinical features of DMD, to describe current outcome measures used in clinical studies, and to highlight new emerging therapies for affected individuals.

Fat Embolism Syndrome in Duchenne Muscular Dystrophy Patients: Early Recognition and Aggressive Therapy

We describe two pediatric patients with Duchenne muscular dystrophy that presented with acute neurologic deterioration and hypoxic respiratory failure requiring mechanical ventilation. These cases fulfill the clinical criteria for Fat Embolism Syndrome. Early recognition and aggressive supportive therapy with mechanical ventilation, right ventricular afterload reduction, and blood transfusion led to survival without any residual effects from the event. Fat Embolism Syndrome needs to be considered early in the course of patients with Duchenne muscular dystrophy who present with respiratory and neurological symptoms.

The Relationship Between Bone Mineral Density and Cardiovascular Function in Duchenne Muscular Dystrophy: A Retrospective Cohort Study

INTRODUCTION:

Duchenne muscular dystrophy (DMD) is an X-linked genetic disorder that causes progressive skeletal and cardiac muscle weakness in boys. Cardiac dysfunction is a frequent cause of death in DMD. Glucocorticoids are the standard of care in DMD. The long-term use of oral glucocorticoids in DMD is complicated by poor bone health. Epidemiological studies suggest a biological link between the loss of bone mineral density (BMD) and cardiovascular disease, including coronary artery and cerebrovascular diseases. Whether an association between low BMD and cardiac dysfunction occurs in DMD boys has not yet been studied. The objective of this retrospective cohort study was to examine the relationship between BMD and cardiovascular health in DMD.

METHODS:

Retrospective data analyses was performed from de-identified medical records from a tertiary academic medical center. Whole body BMD was measured using dual-energy xray absorptiometry (DEXA) scan and left ventricular ejection fraction (LVEF) was measured using echocardiogram. Linear regression was used to evaluate the relationship between BMD and LVEF.

RESULTS:

Data was analyzed from a total of 32 boys with DMD. The mean age at which baseline BMD measurements was obtained of 11±3 (SD) years. The worst LVEF was measured at a mean of 23.7±21.8 (SD) months after the baseline BMD measurement. The final adjusted linear regression of the relationship between baseline BMD z-score and worst LVEF was not statistically significant (ß=0.41, p‑value=0.6455).

DISCUSSION:

In this cohort of boys with DMD, BMD was not associated with LVEF dysfunction up to 79 months later. Future research with a longer longitudinal follow-up period is warranted to evaluate the relationship between BMD and cardiovascular disease in DMD.

Bone Mineral Density and Bone Metabolism in Patients with Duchenne Muscular Dystrophy

OBJECTIVE

Poor bone health with related morbidity is a major problem with Duchene Muscular Dystrophy (DMD). Decreased mobility and long-term corticosteroid therapy are involved in poor bone health in DMD. We investigated bone mineral density and bone metabolism in 30 steroid treated DMD patients and also compared mentioned factors between ambulated and non-ambulated patients.

MATERIALS & METHODS

In this cross-sectional study, 30 boys (21 patients ambulate and 9 non-ambulate) with documented DMD, according to genetic analysis, were enrolled in 2015. Demographic characteristics, neurologic exam findings, muscle function score, corticosteroid dose and duration and food frequency questionnaire were recorded. Bone mineral density was measured with dual- energy X-ray absorptiometry (DEXA) on lumbar spine and left proximal femur. Serum 25-hydroxyvitamin D, calcium, phosphorus and parathyroid hormone (PTH) levels were measured.

RESULTS

Osteoporosis was found in 86.7% patients. Mean bone density in the lumbar spine was -1.5±0.24 and -1.4±0.27 in ambulates and non-ambulates respectively (P=0.7). Mean bone density at proximal femur was -3.4±0.2 in ambulates and -3.4±0.3 in non-ambulates (P =0.48). Intra-groups statistical analysis showed significant difference between bone mineral density at lumbar spine and proximal femur in both mentioned groups (P<0.05). Vitamin D deficiency was detected in 13 patients (43.3%) and its serum level was significantly lower in non-ambulates compared with ambulates.

CONCLUSION

Considering high prevalence of vitamin D deficiency and osteoporosis in DMD patients, it seems vitamin D supplementation can improve vitamin D status and osteoporosis in these patients, especially in non-ambulates.

Fat embolism after fractures in Duchenne muscular dystrophy: an underdiagnosed complication? A systematic review

Duchenne muscular dystrophy is the most frequent lethal genetic disease. Several clinical trials have established both the beneficial effect of steroids in Duchenne muscular dystrophy and the well-known risk of side effects associated with their daily use. For many years it has been known that steroids associated with ambulation loss lead to obesity and also damage the bone structure resulting in the bone density reduction and increased incidence of bone fractures and fat embolism syndrome, an underdiagnosed complication after fractures. Fat embolism syndrome is characterized by consciousness disturbance, respiratory failure and skin rashes. The use of steroids in Duchenne muscular dystrophy may result in vertebral fractures, even without previous trauma. Approximately 25% of patients with Duchenne muscular dystrophy have a long bone fracture, and 1% to 22% of fractures have a chance to develop fat embolism syndrome. As the patients with Duchenne muscular dystrophy have progressive cardiac and respiratory muscle dysfunction, the fat embolism may be unnoticed clinically and may result in increased risk of death and major complications. Different treatments and prevention measures of fat embolism have been proposed; however, so far, there is no efficient therapy. The prevention, early diagnosis and adequate symptomatic treatment are of paramount importance. The fat embolism syndrome should always be considered in patients with Duchenne muscular dystrophy presenting with fractures, or an unexplained and sudden worsening of respiratory and cardiac symptoms.

WHOLE-BODY VIBRATION EXERCISE IS WELL TOLERATED IN PATIENTS WITH DUCHENNE MUSCULAR DYSTROPHY: A SYSTEMATIC REVIEW

BACKGROUND

Duchenne muscular dystrophy (DMD) is caused by a defective gene located on the X-chromosome, responsible for the production of the dystrophin protein. Complications in the musculoskeletal system have been previously described in DMD patients. Whole body vibration exercise (WBVE) is a treatment that improves musculoskeletal function in movement disorders. The aim of this study was to review the effects of WBVE on functional mobility, bone and muscle in DMD patients.

MATERIALS AND METHODS

Four databases were searched. Three eligible studies were found; all three conclude the management of DMD patients with WBV was clinically well tolerated. The studies used a side-alternating WBV system, frequencies 7 - 24 Hz; and amplitudes 2 - 4 mm.

RESULTS

A work indicates that a temporary increase in creatine kinase in DMD during the first days of WBV was observed, but other authors did not find changes. No significant changes in bone mass, muscle strength or bone markers. Some patients reported subjective functional improvement during training. Interpretation.

CONCLUSION

It is concluded that WBV seems to be a feasible and well tolerated exercise modality in DMD patients.

Prophylactic pamidronate partially protects from glucocorticoid-induced bone loss in the mdx mouse model of Duchenne muscular dystrophy

Glucocorticoids are extensively used to treat patients with Duchenne muscular dystrophy because of their ability to delay muscle damage, prolong ambulation and extend life. However, use of glucocorticoids significantly increases bone loss, fragility and fractures. To determine if antiresorptive bisphosphonates could prevent the effects of glucocorticoids on bone quality, we used dystrophic mdx mice treated with the glucocorticoid prednisone during 8weeks of rapid bone growth from 5 to 13weeks of age and treated some mice with the bisphosphonate pamidronate during the first two weeks of prednisone administration. Prednisone reduced long bone growth, decreased cortical bone thickness and area and decreased the strength of the femurs. Pamidronate treatment protected mice from cortical bone loss but did not increase bone strength. The combination of prednisone and pamidronate inhibited remodeling of metaphyseal trabecular bone with large numbers of trabeculae containing remnants of calcified cartilage. Prednisone improved muscle strength in the mdx mice and decreased serum creatine kinase with evidence of improved muscle histology and these effects were maintained in mice treated with pamidronate.

Bone health measures in glucocorticoid-treated ambulatory boys with Duchenne muscular dystrophy

Osteoporosis is a major problem in boys with Duchenne Muscular Dystrophy (DMD), attributable to muscle weakness and glucocorticoid therapy. Consensus regarding bone health assessment and management is lacking. Lumbar spine areal bone mineral density (defined as bone mass per area of bone) by dual-energy X-ray absorptiometry (DXA) is frequently the primary measure used, but has limitations for boys with DMD. We retrospectively studied 292 ambulant glucocorticoid-treated boys with DMD categorized by functional mobility score, FMS 1, 2 or 3. We assessed DXA whole body and lumbar spine areal bone mineral density and content Z-scores adjusted for age and height, lateral distal femur areal bone mineral density Z-scores, frequency of fractures, and osteoporosis by International Society for Clinical Densitometry 2013 criteria. Whole body and femoral DXA indices decreased, while spine fractures increased, with declining motor function. Lumbar spine areal bone mineral density Z-scores appeared to improve with declining motor function. Bone mineral content Z-scores were consistently lower than corresponding bone mineral density Z-scores. Our findings highlight the complexity of assessing bone health in boys with DMD. Bone health indices worsened with declining motor function in ambulant boys, but interpretation was affected by measure and skeletal site examined. Whole body bone mineral content may be a valuable measure in boys with DMD. Lumbar spine areal bone mineral density Z-score as an isolated measure could be misleading. Comprehensive management of osteoporosis in boys with DMD should include vertebral fracture assessment.

Histomorphometry and Bone Matrix Mineralization Before and After Bisphosphonate Treatment in Boys With Duchenne Muscular Dystrophy: A Paired Transiliac Biopsy Study

Duchenne muscular dystrophy (DMD) is a genetic disorder causing progressive muscle weakness. To prolong independent ambulation, DMD patients are treated with glucocorticoids, which, in turn, can increase bone fragility. In a cohort with vertebral fractures, intravenous bisphosphonate (iv BP) therapy stabilized vertebrae and reduced back pain. To characterize the effects of glucocorticoid therapy and bisphosphonate treatment on bone tissue and material properties, paired transiliac biopsy samples (before and after on average 2.4 years of iv BP) from 9 boys with DMD were studied for histomorphometry and bone mineralization density distribution (BMDD) and compared to reference values. Before iv BP, the boys had low cancellous bone volume (BV/TV) and cortical thickness (Ct.Wi) (both on average 56% of the healthy average, p < 0.001 versus reference), and mineralizing surface (MS/BS) in the lower normal range (on average 74% of the healthy average). The average degree of mineralization of cancellous (Cn.CaMean) and cortical compartments (Ct.CaMean) was 21.48 (20.70, 21.90) wt% and 20.42 (19.32, 21.64) wt%, respectively (median [25th, 75th percentiles]), which was not different from reference. After iv BP, BV/TV and Ct.Wi were, on average, unchanged. However, at the individual patient level, BV/TV Z-scores increased in 2, remained unchanged in 4, and declined in 3 patients. Additionally, on average, MS/BS decreased (-85%, p < 0.001), Cn.CaMean (+2.7%) increased, whereas the heterogeneity of cancellous (Cn.CaWidth -19%) and cortical bone mineralization (Ct.CaWidth -8%, all p < 0.05) decreased versus baseline. The changes in bone mineralization are consistent with the antiresorptive action of iv BP. At the same time, our observations point to the need for novel therapies with less or absent bone turnover suppression, including the fact that bone turnover was low even before bisphosphonate therapy, that bone turnover declined further (as expected) with treatment, and that declines in trabecular bone volume were observed in some boys despite bisphosphonate therapy. © 2015 American Society for Bone and Mineral Research.

Positive effects of bisphosphonates on bone and muscle in a mouse model of Duchenne muscular dystrophy

Patients with Duchenne muscular dystrophy are at increased risk of decreased bone mineral density and bone fracture as a result of inactivity. To determine if antiresorptive bisphosphonates could improve bone quality and their effects on muscle we studied the Mdx mouse, treated with pamidronate during peak bone growth at 5 and 6 weeks of age, and examined the outcome at 13 weeks of age. Pamidronate increased cortical bone architecture and strength in femurs with increased resistance to fracture. While overall long bone growth was not affected by pamidronate, there was significant inhibition of remodeling in metaphyseal trabecular bone with evidence of residual calcified cartilage. Pamidronate treatment had positive effects on skeletal muscle in the Mdx mice with decreased serum and muscle creatine kinase and evidence of improved muscle histology and grip strength.

Pharmacological therapies for muscular dystrophies

PURPOSE OF REVIEW

The study reviews recent advances in pharmacological management of muscular dystrophies. Similarities and differences among the pathophysiology of different forms of muscular dystrophy lead to a broad array of approaches to provide new treatments.

RECENT FINDINGS

In this review, we include only those muscular dystrophies for which advances have been published in the past year. This represents the 'advancing edge' of a large body of research over more than 20 years. This runs the gamut of new discoveries in symptomatic management to mutation-specific strategies that attempt to correct the root cause of the disorder.

SUMMARY

The field of pharmacological therapies for the muscular dystrophies continues to steadily advance. It is encouraging that research into new therapies is increasingly exploring pharmacological strategies with the potential to ameliorate disease pathology to a clinically significant degree.

Bone health and associated metabolic complications in neuromuscular diseases

This article reviews the recent literature regarding bone health as it relates to the patient living with neuromuscular disease (NMD). Studies defining the scope of bone-related disease in NMD are scant. The available evidence is discussed, focusing on abnormal calcium metabolism, increased fracture risk, and the prevalence of both scoliosis and hypovitaminosis D in Duchenne muscular dystrophy, amyotrophic lateral sclerosis, and spinal muscular atrophy. Future directions are discussed, including the urgent need for studies both to determine the nature and extent of poor bone health, and to evaluate the therapeutic effect of available osteoporosis treatments in patients with NMD.