Pulmonary Endpoints in Duchenne Muscular Dystrophy. A Workshop Summary

Definition of diaphragmatic sleep disordered breathing and clinical meaning in Duchenne muscular dystrophy

BACKGROUND

Diaphragmatic sleep disordered breathing (dSDB) has been recently identified as sleep dysfunction secondary to diaphragmatic weakness in Duchenne muscular dystrophy (DMD). However, scoring criteria for the identification of dSDB are missing.This study aimed to define and validate dSDB scoring criteria and to evaluate whether dSDB severity correlates with respiratory progression in DMD.

METHODS

Scoring criteria for diaphragmatic apnoea (dA) and hypopnoeas (dH) have been defined by the authors considering the pattern observed on cardiorespiratory polygraphy (CR) and the dSDB pathophysiology.10 sleep professionals (physiologists, consultants) blinded to each other were involved in a two-round Delphi survey to rate each item of the proposed dSDB criteria (Likert scale 1-5) and to recognise dSDB among other SDB. The scorers' accuracy was tested against the authors' panel.Finally, CR previously conducted in DMD in clinical setting were rescored and diaphragmatic Apnoea-Hypopnoea Index (dAHI) was derived. Pulmonary function (forced vital capacity per cent of predicted, FVC%pred), overnight oxygen saturation (SpO2) and transcutaneous carbon dioxide (tcCO2) were correlated with dAHI.

RESULTS

After the second round of Delphi, raters deemed each item of dA and dH criteria as relevant as 4 or 5. The agreement with the panel in recognising dSDB was 81%, kappa 0.71, sensitivity 77% and specificity 85%.32 CRs from DMD patients were reviewed. dSDB was previously scored as obstructive. The dAHI negatively correlated with FVC%pred (r=-0.4; p<0.05). The total number of dA correlated with mean overnight tcCO2 (r 0.4; p<0.05).

CONCLUSIONS

dSDB is a newly defined sleep disorder that correlates with DMD progression. A prospective study to evaluate dSDB as a respiratory measure for DMD in clinical and research settings is planned.

Genetic therapies and respiratory outcomes in patients with neuromuscular disease

PURPOSE OF REVIEW

Genetic therapies made a significant impact to the clinical course of patients with spinal muscular atrophy and Duchenne muscular dystrophy. Clinicians and therapists who care for these patients want to know the changes in respiratory sequelae and implications for clinical care for treated patients.

RECENT FINDINGS

Different genetic therapy approaches have been developed to replace the deficient protein product in spinal muscular atrophy and Duchenne muscular dystrophy. The natural history of these conditions needed to be understood in order to design clinical trials. Respiratory parameters were not the primary outcome measures for the clinical trials. The impact of these therapies is described in subsequent clinical trial reports or real-world data.

SUMMARY

Genetic therapies are able to stabilize or improve the respiratory sequelae in patients with spinal muscular atrophy and Duchenne muscular dystrophy. Standardized reporting of these outcomes is needed to help inform the future revisions of clinical standards of care and practice guidelines.

Draft Guidance for Industry Duchenne Muscular Dystrophy, Becker Muscular Dystrophy, and Related Dystrophinopathies - Developing Potential Treatments for the Entire Spectrum of Disease

Background

Duchenne muscular dystrophy (DMD) and related dystrophinopathies are neuromuscular conditions with great unmet medical needs that require the development of effective medical treatments.

Objective

To aid sponsors in clinical development of drugs and therapeutic biological products for treating DMD across the disease spectrum by integrating advancements, patient registries, natural history studies, and more into a comprehensive guidance.

Methods

This guidance emerged from collaboration between the FDA, the Duchenne community, and industry stakeholders. It entailed a structured approach, involving multiple committees and boards. From its inception in 2014, the guidance underwent revisions incorporating insights from gene therapy studies, cardiac function research, and innovative clinical trial designs.

Results

The guidance provides a deeper understanding of DMD and its variants, focusing on patient engagement, diagnostic criteria, natural history, biomarkers, and clinical trials. It underscores patient-focused drug development, the significance of dystrophin as a biomarker, and the pivotal role of magnetic resonance imaging in assessing disease progression. Additionally, the guidance addresses cardiomyopathy's prominence in DMD and the burgeoning field of gene therapy.

Conclusions

The updated guidance offers a comprehensive understanding of DMD, emphasizing patient-centric approaches, innovative trial designs, and the importance of biomarkers. The focus on cardiomyopathy and gene therapy signifies the evolving realm of DMD research. It acts as a crucial roadmap for sponsors, potentially leading to improved treatments for DMD.

Factors Associated with Respiratory Health and Function in Duchenne Muscular Dystrophy: A Systematic Review and Evidence Grading

BACKGROUND

Despite advances in the medical management of the disease, respiratory involvement remains a significant source of morbidity and mortality in children and adults with Duchenne muscular dystrophy (DMD).

OBJECTIVE

The objective of this systematic literature review was to synthesize and grade published evidence of factors associated with respiratory health and function in DMD.

METHODS

We searched MEDLINE, Embase, and the Cochrane Library for records of studies published from January 1, 2000 (to ensure relevance to current care practices), up until and including December 31, 2022, reporting evidence of prognostic indicators and predictors of disease progression in DMD. The quality of evidence (i.e., very low to high) was assessed using the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) framework.

RESULTS

The bibliographic search strategy resulted in the inclusion of 29 articles. In total, evidence of 10 factors associated with respiratory health and function in patients with DMD was identified: glucocorticoid exposure (high- to very low-quality evidence), DMD mutations (low-quality evidence), DMD genetic modifiers (low-quality evidence), other pharmacological interventions (i.e., ataluren, eteplirsen, idebenone, and tamoxifen) (moderate- to very low-quality evidence), body mass index and weight (low-quality evidence), and functional ability (low-quality evidence).

CONCLUSIONS

In conclusion, we identified a total of 10 factors associated with respiratory health in function in DMD, encompassing both pharmacological therapies, genetic mutations and modifiers, and patient clinical characteristics. Yet, more research is needed to further delineate sources of respiratory heterogeneity, in particular the genotype-phenotype association and the impact of novel DMD therapies in a real-world setting. Our synthesis and grading should be helpful to inform clinical practice and future research of this heavily burdened patient population.

The role of lung volume recruitment therapy in neuromuscular disease: a narrative review

Respiratory muscle weakness results in substantial discomfort, disability, and ultimately death in many neuromuscular diseases. Respiratory system impairment manifests as shallow breathing, poor cough and associated difficulty clearing mucus, respiratory tract infections, hypoventilation, sleep-disordered breathing, and chronic ventilatory failure. Ventilatory support (i.e., non-invasive ventilation) is an established and key treatment for the latter. As survival outcomes improve for people living with many neuromuscular diseases, there is a shift towards more proactive and preventative chronic disease multidisciplinary care models that aim to manage symptoms, improve morbidity, and reduce mortality. Clinical care guidelines typically recommend therapies to improve cough effectiveness and mobilise mucus, with the aim of averting acute respiratory compromise or respiratory tract infections. Moreover, preventing recurrent infective episodes may prevent secondary parenchymal pathology and further lung function decline. Regular use of techniques that augment lung volume has similarly been recommended (volume recruitment). It has been speculated that enhancing lung inflation in people with respiratory muscle weakness when well may improve respiratory system "flexibility", mitigate restrictive chest wall disease, and slow lung volume decline. Unfortunately, clinical care guidelines are based largely on clinical rationale and consensus opinion rather than level A evidence. This narrative review outlines the physiological changes that occur in people with neuromuscular disease and how these changes impact on breathing, cough, and respiratory tract infections. The biological rationale for lung volume recruitment is provided, and the clinical trials that examine the immediate, short-term, and longer-term outcomes of lung volume recruitment in paediatric and adult neuromuscular diseases are presented and the results synthesised.

Pamrevlumab, a Fully Human Monoclonal Antibody Targeting Connective Tissue Growth Factor, for Non-Ambulatory Patients with Duchenne Muscular Dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) is a neuromuscular disease stemming from dystrophin gene mutations. Lack of dystrophin leads to progressive muscle damage and replacement of muscle with fibrotic and adipose tissue. Pamrevlumab (FG-3019), a fully human monoclonal antibody that binds to connective tissue growth factor (CTGF), is in Phase III development for treatment of DMD and other diseases.

METHODS

MISSION (Study 079; NCT02606136) was an open-label, Phase II, single-arm trial of pamrevlumab in 21 non-ambulatory patients with DMD (aged≥12 years, receiving corticosteroids) who received 35-mg/kg intravenous infusions every 2 weeks for 2 years. The primary endpoint was change from baseline in percent predicted forced vital capacity (ppFVC). Secondary endpoints included other pulmonary function tests, upper limb function and strength assessments, and changes in upper arm fat and fibrosis scores on magnetic resonance imaging.

RESULTS

Fifteen patients completed the trial. Annual change from baseline (SE) in ppFVC was -4.2 (0.7) (95% CI -5.5, -2.8). Rate of decline in ppFVC in pamrevlumab-treated patients was slower than observed in historical published trials of non-ambulatory patients. MISSION participants experienced slower-than-anticipated muscle function declines compared with natural history and historical published trials of non-ambulatory patients with DMD. Pamrevlumab was well-tolerated. Treatment-emergent adverse events were mild to moderate, and none led to study discontinuation.

CONCLUSIONS

nti-CTGF therapy with pamrevlumab represents a potential treatment for DMD. The lack of internal control group limits the results.

Spirometry correlates with physical activity in patients with Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) is associated with progressive muscle weakness and respiratory decline. To date, studies have focused on respiratory decline and loss of ambulation as a metric of loss of skeletal muscle strength. However, new functional measures can assess skeletal muscle disease regardless of ambulatory status. The relationship between these tests and concurrent lung function is currently unexplored.

OBJECTIVE

To assess the correlation between spirometry measurements and functional muscle assessments such as accelerometry and quantitative muscle testing (QMT).

METHODS

Enrolled patients with DMD underwent accelerometry and QMT at study clinic visits. Any pulmonary function testing within 6 months of visit was obtained from the electronic medical record. The Spearman correlation coefficient was used to assess the relationship between spirometry and functional muscle testing.

RESULTS

Forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1 ) demonstrated the strongest correlation with accelerometry. Both FVC and FEV1 showed a similar relationship to accelerometry when activity was divided into intensity categories, with low intensity and moderate-to-vigorous activity categories showing the strongest correlation. Maximal expiratory pressure (MEP) and FVC showed the most robust correlations with total QMT (p < 0.001 and p < 0.01, respectively).

CONCLUSION

Lung function, specifically FVC percent predicted and FEV1 %p, shows a good correlation with upper and lower extremity skeletal muscle functional testing such as accelerometry and QMT.

The Association between the Respiratory System and Upper Limb Strength in Males with Duchenne Muscular Dystrophy: A New Field for Intervention?

Progressive, irreversible muscle weakness is the leading symptom of Duchenne muscular dystrophy (DMD), often resulting in death from respiratory muscle failure. Little is known about the relationship between the functioning of the respiratory system and the hand grip-a function which remains long preserved. This study aimed to investigate the interdependence between muscle strength and the function of both hand grip and the respiratory system in patients with DMD.

MATERIALS AND METHOD

The study included cohort patients, aged 6-17, with DMD, recruited from the Rare Disease Centre, Gdansk, Poland. Clinical status (Vignos scale, Brook scale), pulmonary function (respiratory muscle strength-MIP, MEP); spirometry (FEV1; FVC), as well as upper limb function (performance of the upper limb-PUL 2.0) and hand grip strength (HGS) (hand-held dynamometer) were evaluated in all participants.

RESULTS

Finally, 53 boys (mean age 11.41 ± 3.70 years, 25 non-ambulant) were included. Each of the participants presented a lower %pv of MIP (48.11 ± 27), MEP (38.11 ± 22), PUL (75.64 ± 27), and HGS (33.28 ± 18). There were differences between the ambulatory and non-ambulatory groups in values of MIP, MEP, FVC, PUL, HGS (p < 0.001 for all), and FEV1 (p < 0.013). There were correlations between PUL, HGS, and MIP (R = 0.56; R = 0.61, p < 0.001 both), MEP (R = 0.59; R = 0.62, p < 0.001), FVC (R = 0.77; R = 0.77, p < 0.001), and FEV1 (R = 0.77; R = 0.79; p < 0.001). These correlations were found for all participants, but non-ambulatory patients presented stronger relationships.

CONCLUSIONS

1. The pulmonary and upper limb functions were within the normal range in ambulatory and low in non-ambulatory patients with DMD, but the muscle strength of both systems was low, regardless of the stage of the disease. 2. There seems to be an interdependence between the respiratory system and upper limb strength in terms of muscle strength and function in DMD patients, which is stronger in non-ambulatory patients. This may be the basis for the creation of a new personalized plan in rehabilitation-the simultaneous rehabilitation of the respiratory and upper limb muscles. Further studies on this theory should be conducted.

Prediction of height using ulna length in African-Caribbean children

Standing height is an essential anthropometric measurement in pediatrics. In children unable to stand upright, measurement of ulna to predict standing height is recommended, but height prediction equations based on the ulna have not been established in children of African ancestry. We hypothesized that such equations would result in lower predicted height compared to using equations derived from non-African children. We measured prospectively standing height and both ulna in 358 African-Caribbean children without bone deformity or muscle disease, referred to two pulmonary function test laboratories. Interobserver variability was low for standing height (n = 54) and ulna measurement (n = 51) (mean biases [95%CI]: -0.02 [-0.99; 0.95] and 0.05 [-0.91; 1.01] cm, respectively), as well as inter-ulna variability (n = 352; mean bias 0.03 95%CI [-0.66; 0.73] cm). We used the mean value of 247 bilateral ulna measurements to calculate prediction equations using a generalized linear model including age, sex, ulna length, and geographic origin group, the latter showing no influence on the model. In the validation population of 107 children, the median difference [inter-quartile range] between standing height and ulna-predicted height was -0.4 [-2.7; 1.0] cm. Of 260 reliable baseline spirometry, there was a strong concordance between bronchial obstruction diagnosis established using standing height or ulna-predicted height (kappa coefficient: 0.85 [0.77; 0.94]) with only 11 (4.3%) children misclassified. The ulna predicted height calculated from African-Caribbean prediction equations resulted in a smaller height than the height calculated using equations derived from non-African children.

Respiratory Function and Sleep Disordered Breathing in Pediatric Duchenne Muscular Dystrophy

BACKGROUND

The decline of respiratory function in Duchenne muscular dystrophy (DMD) is associated with sleep disordered breathing (SDB) and alteration of nocturnal gas exchange, first manifesting as nocturnal hypoventilation (NH). However, the correlation between pulmonary function measured by spirometry (PFT) and the onset of SDB with or without NH is unclear.

AIM

To identify the prevalence and features of SDB and to investigate the relationship between lung function determined by forced vital capacity (FVC) and sleep abnormalities in a large paediatric DMD population.

METHODS

Retrospective, single-center cohort study. FVC% predicted (FVC%) was calculated using predicted equations from the Global Lung Function Initiative. NH was defined by transcutaneous (tc) CO2 >50 mmHg for >25% of total sleep time (TST); borderline NH by a mean tcCO2 between 45-50mmHg or tcCO2>50mmHg for ≤25% of TST; Clinically meaningful obstructive sleep apnea (OSA) by obstructive Apnea-Hypopnea Index >5. The sensitivity, specificity, positive and negative predictive value of FVC<50% to indicate presence of nocturnal hypoventilation were calculated.

RESULTS

134 patients underwent 284 sleep studies and 1222 PFT. Mean (SD) age at first and last sleep study was 12.9 (2.7) and 14.3 (2.6) years. Borderline NH (n=31) was detected in both ambulant and early-non ambulant subjects, while 100% of NH cases (n=14) were non-ambulant. NH was detected in 4/14 patients despite an FVC>50%. Seventeen/26 patients with OSA presented with concomitant NH or borderline NH. FVC<50% was associated with NH indicating a sensitivity and specificity of 73% and 86%, respectively. Positive and negative predictive value were 32% and 97% respectively. PFT showed a non-linear, sudden FVC% decline in 18% of cases.

CONCLUSIONS

FVC% <50 was associated with NH in close to a third of patients. CO2 elevation can be associated with obstructive/pseudo-obstructive events and was also observed in early non-ambulant cases or in the presence of FVC>50%. These results are relevant for the clinical management of SDB.

Delays in pulmonary decline in eteplirsen-treated patients with Duchenne muscular dystrophy

INTRODUCTION/AIMS

Pulmonary decline is an important issue in patients with Duchenne muscular dystrophy (DMD). Eteplirsen is a US-approved treatment for patients with DMD and exon 51 skip-amenable mutations. Previous analyses have shown that eteplirsen is associated with statistically significant attenuation of pulmonary decline. This study evaluates the effect of eteplirsen treatment from newly available data sources on pulmonary function over time in patients with DMD.

METHODS

This study uses a post hoc pooled analysis to compare the percentage of predicted forced vital capacity (FVC%p) and projected time to pulmonary function milestones in patients with DMD and exon 51 skip-amenable mutations receiving eteplirsen (Studies 204 and 301) or standard of care (SoC; Cooperative International Neuromuscular Research Group Duchenne Natural History Study). A mixed model for repeated measures framework was applied to evaluate the impact of eteplirsen.

RESULTS

An average annual rate of FVC%p decline for eteplirsen-treated patients was estimated to be 3.47%, which was a statistically significant attenuation from the 5.95% rate of decline estimated in SoC patients (P = 0.0001). Using linear extrapolations of the model-estimated decline in FVC%p, the attenuation in FVC%p decline for eteplirsen-treated patients corresponded to a delay of 5.72 years in time to needing continuous ventilation, 3.31 years in time to needing nighttime ventilation, and 2.11 years in time to needing a cough assist device compared with SoC patients.

DISCUSSION

The attenuation of FVC%p decline suggests that eteplirsen-treated patients experienced statistically significant and clinically meaningful attenuations in pulmonary decline compared with SoC patients. This article is protected by copyright. All rights reserved.

Leveraging Cardiac Magnetic Resonance Imaging to Assess Skeletal Muscle Progression in Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is characterized by muscle deterioration and progressive weakness. As a result, patients with DMD have significant cardiopulmonary morbidity and mortality that worsens with age and loss of ambulation. Since most validated muscle assessments require ambulation, new functional measures of DMD progression are needed. Despite several evaluation methods available for monitoring disease progression, the relationship between these measures is unknown. We sought to assess the correlation between imaging metrics obtained from cardiac magnetic resonance imaging (CMR) and functional assessments including quantitative muscle testing (QMT), spirometry, and accelerometry. Forty-nine patients with DMD were enrolled and underwent CMR, accelerometry and QMT at baseline, 1-year and 2-year clinic visits with temporally associated pulmonary function testing obtained from the medical record. Imaging of the upper extremity musculature (triceps and biceps) demonstrated the most robust correlations with accelerometry (p<0.03), QMT (p<0.02) and spirometry (p<0.01). T₁-mapping of serratus anterior muscle showed a similar, but slightly weaker relationship with accelerometry and QMT. T₂-mapping of serratus anterior demonstrated weak indirect correlation with aspects of accelerometry. These images are either routinely obtained in standard CMR or can be added to a protocol and may allow for a more comprehensive assessment of a patient's disease progression.

Genotype-related respiratory progression in Duchenne muscular dystrophy-A multicenter international study

INTRODUCTION/AIMS

Mutations amenable to skipping of specific exons have been associated with different motor progression in Duchenne muscular dystrophy (DMD). Less is known about their association with long-term respiratory function. In this study we investigated the features of respiratory progression in four DMD genotypes relevant in ongoing exon-skipping therapeutic strategies.

METHODS

This was a retrospective longitudinal study including DMD children followed by the UK NorthStar Network and international AFM Network centers (May 2003 to October 2020). We included boys amenable to skip exons 44, 45, 51, or 53, who were older than 5 years of age and ambulant at first recorded visit. Subjects who were corticosteroid-naive or enrolled in interventional clinical trials were excluded. The progression of respiratory function (absolute forced vital capacity [FVC] and calculated as percent predicted [FVC%]) was compared across the four subgroups (skip44, skip45, skip51, skip53).

RESULTS

We included 142 boys in the study. Mean (standard deviation) age at first visit was 8.6 (2.5) years. Median follow-up was 3 (range, 0.3-8.3) years. In skip45 and skip51, FVC% declined linearly from the first recorded visit. From the age of 9 years, FVC% declined linearly in all genotypes. Skip44 had the slowest (2.7%/year) and skip51 the fastest (5.9%/year) annual FVC% decline. The absolute FVC increased progressively in skip44, skip45, and skip51. In skip53, FVC started declining from 14 years of age.

DISCUSSION

The progression of respiratory dysfunction follows different patterns for specific genotype categories. This information is valuable for prognosis and for the evaluation of exon-skipping therapies.

The effect of emerging molecular and genetic therapies on cardiopulmonary disease in Duchenne muscular dystrophy

Gene therapy is an attractive approach being intensively studied to prevent muscle deterioration in patients with Duchenne muscular dystrophy. While clinical trials are only in early stages, initial reports are promising for its effects on ambulation. Cardiopulmonary failure, however, is the most common cause of mortality in Duchenne muscular dystrophy (DMD) patients, and little is known regarding the prospects for gene therapy on alleviating DMD-associated cardiomyopathy and respiratory failure. Here we review current knowledge regarding effects of gene therapy on DMD cardiomyopathy and discuss respiratory endpoints that should be considered as outcome measures in future clinical trials.

Suitability of external controls for drug evaluation in Duchenne muscular dystrophy

Objective

To evaluate the suitability of real-world data (RWD) and natural history data (NHD) for use as external controls in drug evaluations for ambulatory Duchenne muscular dystrophy (DMD).

Methods

The consistency of changes in the 6-minute walk distance (Δ6MWD) was assessed across multiple clinical trial placebo arms and sources of NHD/RWD. Six placebo arms reporting 48-week Δ6MWD were identified via literature review and represented 4 sets of inclusion/exclusion criteria (n = 383 patients in total). Five sources of RWD/NHD were contributed by Universitaire Ziekenhuizen Leuven, DMD Italian Group, The Cooperative International Neuromuscular Research Group, ImagingDMD, and the PRO-DMD-01 study (n = 430 patients, in total). Mean Δ6MWD was compared between each placebo arm and RWD/NHD source after subjecting the latter to the inclusion/exclusion criteria of the trial for baseline age, ambulatory function, and steroid use. Baseline covariate adjustment was investigated in a subset of patients with available data.

Results

Analyses included ∼1,200 patient-years of follow-up. Differences in mean Δ6MWD between trial placebo arms and RWD/NHD cohorts ranged from −19.4 m (i.e., better outcomes in RWD/NHD) to 19.5 m (i.e., worse outcomes in RWD/NHD) and were not statistically significant before or after covariate adjustment.

Conclusions

We found that Δ6MWD was consistent between placebo arms and RWD/NHD subjected to equivalent inclusion/exclusion criteria. No evidence for systematic bias was detected. These findings are encouraging for the use of RWD/NHD to augment, or possibly replace, placebo controls in DMD trials. Multi-institution collaboration through the Collaborative Trajectory Analysis Project rendered this study feasible.

Therapies that are available and under development for Duchenne muscular dystrophy: What about lung function?

BACKGROUND

Respiratory failure is the principal source of morbidity and mortality among patients with Duchenne muscular dystrophy exerting a negative influence on their total quality of life. The aim of this review is to provide systematically current literature evidence about the effects of different treatment options (available or under development) for Duchenne muscular dystrophy on the pulmonary function of these patients.

METHODS

A comprehensive search was undertaken using multiple health-related databases, while two independent reviewers assessed the eligibility of studies. A third person addressed any disagreements between reviewers. The quality of the methodology of the included studies was also assessed.

RESULTS

A total of 19 original research papers (nine evaluating the role of steroids, six idebenone, three eteplirsen, one stem-cell therapy, and one ataluren) were found to fulfill our selection criteria with the majority of them (14 of 19) being prospective studies, not always including a control group. Endpoints mainly used in these studies were values of pulmonary function tests. Current and under development treatments proved to be safe and no significant adverse events were reported. A beneficial impact on pulmonary function was described by authors in the majority of these studies. The principal effect was slowing of lung disease progress, as expressed by spirometric values. However, the risk of bias was introduced in many of the above studies, while high heterogeneity in terms of treatment protocols and outcome measures limits the comparability of the results.

CONCLUSION

Glucocorticoids remain the best-studied pharmacologic therapy for Duchenne muscular dystrophy and very likely delay the expected decline in lung function. With regard to new therapeutic agents, initial study results are encouraging. However, larger clinical trials are needed that minimize the risk of study bias, optimize the comparability of treatment groups, examine clinically meaningful pulmonary outcome measures, and include long-term follow up.

Management of Adrenal Insufficiency Risk After Long-term Systemic Glucocorticoid Therapy in Duchenne Muscular Dystrophy: Clinical Practice Recommendations

Long-term glucocorticoid therapy has improved outcomes in patients with Duchenne muscular dystrophy. However, the recommended glucocorticoid dosage suppresses the hypothalamic-pituitary-adrenal axis, leading to adrenal insufficiency that may develop during severe illness, trauma or surgery, and after discontinuation of glucocorticoid therapy. The purpose of this review is to highlight the risk of adrenal insufficiency in this patient population, and provide practical recommendations for management of adrenal insufficiency, glucocorticoid withdrawal, and adrenal function testing. Strategies to increase awareness among patients, families, and health care providers are also discussed.

Echographic Assessment of Diaphragmatic Function in Duchenne Muscular Dystrophy from Childhood to Adulthood

BACKGROUND

Duchenne muscular dystrophy (DMD) is an X-linked recessive genetic muscle disorder. Respiratory muscle function is classically affected in this disease. Ultrasound recently emerged as a non-invasive tool to assess diaphragm function. However, there are only a few studies using diaphragm ultrasound (US) in DMD.

PURPOSE

We aimed to assess diaphragm ultrasound patterns in DMD, their relationship with age and their association with home mechanical ventilation (HMV).

METHODS

We included DMD patients followed at Raymond Poincaré Hospital who benefited from diaphragm ultrasound and pulmonary function tests.

RESULTS

There were 110 DMD patients and 17 male sex-matched healthy subjects included. In all, 94% of patients were permanent wheelchair users. Median body mass index (BMI) was 18 kg/m2. DMD patients disclosed a reduced forced vital capacity (VC) (12% of predicted value), and 78% of patients were on HMV. In patients, right and left diaphragmatic motions on deep inspiration were reduced and end expiratory diaphragm thickness was borderline normal. In patients, right and left diaphragmatic thickening fractions (TF) were reduced 12.7% and 15.5%, respectively. Age and end expiratory thickness were significantly inversely associated (p = 0.005 for the right diaphragm, p = 0.018 for the left diaphragm). Diaphragm TF was significantly inversely associated with age (p = 0.001 for the right side, p < 0.0001 for the left side). Right and left inspiratory diaphragm motions were significantly inversely associated with age (p < 0.0001).

CONCLUSION

This study describes the severity of diaphragm dysfunction in patients with DMD. Diaphragm US may be a non-invasive outcome measure for DMD.

Long-term data with idebenone on respiratory function outcomes in patients with Duchenne muscular dystrophy

Decline in respiratory function in patients with DMD starts during early teenage years and leads to early morbidity and mortality. Published evidence of efficacy for idebenone on respiratory function outcomes is currently limited to 12 months of follow-up time. Here we report data collected as retrospective cohort study (SYROS) from 18 DMD patients not using glucocorticoids who were treated with idebenone (900 mg/day) under Expanded Access Programs (EAPs). The objective was to assess the long-term respiratory function evolution for periods On-Idebenone compared to periods Off-Idebenone in the same patients. The mean idebenone exposure in the EAPs was 4.2 (range 2.4-6.1) years. The primary endpoint was the annual change in forced vital capacity percent of predicted (FVC%p) compared between Off-Idebenone and On-Idebenone periods. The annual rate of decline in FVC%p was reduced by approximately 50% from -7.4% (95% CI: -9.1, -5.8) for the Off-Idebenone periods to -3.8% (95% CI: -4.8, -2.8) for the On-Idebenone periods (N = 11). Similarly, annual change in peak expiratory flow percent of predicted (PEF%p) was -5.9% (95% CI: -8.0, -3.9) for the Off-Idebenone periods (N = 9) and reduced to -1.9% (95% CI: -3.2, -0.7) for the On-Idebenone periods during the EAPs. The reduced rates of decline in FVC%p and PEF%p were maintained for several years with possible beneficial effects on the rate of bronchopulmonary adverse events, time to 10% decline in FVC%p and risk of hospitalization due to respiratory cause. These long-term data provide Class IV evidence to further support the disease modifying treatment effect of idebenone previously observed in randomized, controlled trials.

Sarcolipin overexpression impairs myogenic differentiation in Duchenne muscular dystrophy

Reduction in the expression of sarcolipin (SLN), an inhibitor of sarco(endo)plasmic reticulum (SR) Ca²⁺-ATPase (SERCA), ameliorates severe muscular dystrophy in mice. However, the mechanism by which SLN inhibition improves muscle structure remains unclear. Here, we describe the previously unknown function of SLN in muscle differentiation in Duchenne muscular dystrophy (DMD). Overexpression of SLN in C₂C₁₂ resulted in decreased SERCA pump activity, reduced SR Ca²⁺ load, and increased intracellular Ca²⁺ (Cai2+) concentration. In addition, SLN overexpression resulted in altered expression of myogenic markers and poor myogenic differentiation. In dystrophin-deficient dog myoblasts and myotubes, SLN expression was significantly high and associated with defective Cai2+ cycling. The dystrophic dog myotubes were less branched and associated with decreased autophagy and increased expression of mitochondrial fusion and fission proteins. Reduction in SLN expression restored these changes and enhanced dystrophic dog myoblast fusion during differentiation. In summary, our data suggest that SLN upregulation is an intrinsic secondary change in dystrophin-deficient myoblasts and could account for the Cai2+ mishandling, which subsequently contributes to poor myogenic differentiation. Accordingly, reducing SLN expression can improve the Cai2+ cycling and differentiation of dystrophic myoblasts. These findings provide cellular-level supports for targeting SLN expression as a therapeutic strategy for DMD.

Imaging respiratory muscle quality and function in Duchenne muscular dystrophy

OBJECTIVE

Duchenne muscular dystrophy (DMD) is characterized by damage to muscles including the muscles involved in respiration. Dystrophic muscles become weak and infiltrated with fatty tissue, resulting in progressive respiratory impairment. The objective of this study was to assess respiratory muscle quality and function in DMD using magnetic resonance imaging and to determine the relationship to clinical respiratory function.

METHODS

Individuals with DMD (n = 36) and unaffected controls (n = 12) participated in this cross sectional magnetic resonance imaging study. Participants underwent dynamic imaging of the thorax to assess diaphragm and chest wall mobility and chemical shift-encoded imaging of the chest and abdomen to determine fatty infiltration of the accessory respiratory muscles. Additionally, clinical pulmonary function measures were obtained.

RESULTS

Thoracic cavity area was decreased in individuals with DMD compared to controls during tidal and maximal breathing. Individuals with DMD had reduced chest wall movement in the anterior-posterior direction during maximal inspirations and expirations, but diaphragm descent during maximal inspirations (normalized to height) was only decreased in a subset of individuals with maximal inspiratory pressures less than 60% predicted. Muscle fat fraction was elevated in all three expiratory muscles assessed (p < 0.001), and the degree of fatty infiltration correlated with percent predicted maximal expiratory pressures (r =  - 0.70, p < 0.001). The intercostal muscles demonstrated minimal visible fatty infiltration; however, this analysis was qualitative and resolution limited.

INTERPRETATION

This magnetic resonance imaging investigation of diaphragm movement, chest wall movement, and accessory respiratory muscle fatty infiltration provides new insights into the relationship between disease progression and clinical respiratory function.

Comparison of Pulmonary Function Decline in Steroid-Treated and Steroid-Naïve Patients with Duchenne Muscular Dystrophy

OBJECTIVE

To describe and compare the lung function decline in patients with Duchenne muscular dystrophy on glucocorticoid therapy in contrast with glucocorticoid-naïve patients, and to define the deciles of pulmonary decline in glucocorticoid-treated patients.

STUDY DESIGN

This retrospective study examined lung function of patients with Duchenne muscular dystrophy over 6 years of age followed between 2001 and 2015 at 2 centers-glucocorticoid-treated patients in Cincinnati, Ohio, and glucocorticoid-naïve patients in Paris, France. Forced vital capacity (FVC, FVC%), forced expiratory volume in 1 second, maximal inspiratory pressure, maximal expiratory pressure, and peak expiratory flow data were analyzed. Only FVC data were available for the French cohort.

RESULTS

There were 170 glucocorticoid-treated patients (92%), 5 patients (2.7%) with past glucocorticoid use, and 50 French glucocorticoid-naïve patients. The peak absolute FVC was higher and was achieved at earlier ages in glucocorticoid-treated compared with glucocorticoid-naïve patients (peak FVC, 2.4 ± 0.6 L vs 1.9 ± 0.7 L; P < .0001; ages 13.5 ± 3.0 years vs 14.3 ± 2.8 years; P = .03). The peak FVC% was also higher and was achieved at earlier ages in glucocorticoid-treated patients (peak FVC%, 105.1 ± 25.1% vs 56 ± 20.9%; P < .0001; ages 11.9 ± 2.9 years vs 13.6 ± 3.2 years; P = .002). Rates of decline for both groups varied with age. Maximal rates of decline were 5.0 ± 0.26% per year (12-20 years) for glucocorticoid-treated and 5.1 ± 0.39% per year for glucocorticoid-naïve patients (11-20 years; P = .2). Deciles of FVC% decline in glucocorticoid-treated patients show that patients experience accelerated decline at variable ages.

CONCLUSIONS

These data describe nonlinear rates of decline of pulmonary function in patients with Duchenne muscular dystrophy, with improved function in glucocorticoid-treated patients. FVC% deciles may be a useful tool for clinical and research use.

Long-term treatment with eteplirsen in nonambulatory patients with Duchenne muscular dystrophy

This analysis aims to describe the outcomes of two nonambulatory patients with Duchenne muscular dystrophy (DMD) who participated in two clinical studies. The two consecutive trials of eteplirsen (studies 201 and 202) were conducted in patients with DMD (N = 12) and confirmed genetic mutations amenable to exon 51 skipping.In study 201, 12 patients were randomized to receive once-weekly, double-blind intravenous infusions of eteplirsen 30 or 50 mg/kg or placebo for 24 weeks; patients then received open-label eteplirsen during weeks 25 through 28. All 12 patients continued onto open-label extension study 202 and received long-term treatment with eteplirsen. We compared cardiac, pulmonary, and upper limb function and dystrophin production in the nonambulatory twin patients versus the 10 ambulatory patients through 240 combined treatment weeks.Ten study patients remained ambulatory through both studies, while the identical twin patients both experienced early, rapid loss of ambulation. The twin patients had greater disease severity at baseline (6-minute walk test [6MWT], 330 and 256 m) versus the other patients (n = 10; 6MWT range, 341-418 m). They maintained cardiac and upper limb function through combined week 240, with outcomes similar to those of the patients who remained ambulatory. Dystrophin production was confirmed following eteplirsen treatment.Despite the loss of ambulation, other markers of disease progression remained relatively stable in the eteplirsen-treated twin patients and were similar to those of the ambulatory patients.

Pulmonary function and clinical correlation in DMD

Duchenne muscular dystrophy [DMD] is the most common inherited myopathy and is caused by a defect in the dystrophin gene on the X chromosome causing production of a dysfunctional dystrophin protein. Over the last decade there have been advances in disease modifying pharmacotherapy beyond the widely used strategy of corticosteroids into products to impact both dystrophin production itself and also some of the downstream effects of absent of dysfunctional dystrophin. This manuscript will explore the respiratory progression of DMD including some proposed functional and clinical correlations and the overlap between loss of function in different muscle groups. Options for symptomatic treatment and support are presented and direction as to when the different options should be considered is provided. The manuscript will also review the currently available and late phase developmental pharmacotherapies for DMD.

Muscular Dystrophies

Muscular dystrophies represent a complex, varied, and important subset of neuromuscular disorders likely to require the care of a pulmonologist. The spectrum of conditions encapsulated by this subset ranges from severe and fatal congenital muscular dystrophies with onset in infancy to mild forms of limb and girdle weakness with onset in adulthood and minimal respiratory compromise. The list and classification of muscular dystrophies are undergoing near-constant revision, based largely on new insights from genetics and molecular medicine. The authors present an overview of the muscular dystrophies, including their basic features, common clinical phenotypes, and important facets of management.

Respiratory and upper limb function as outcome measures in ambulant and non-ambulant subjects with Duchenne muscular dystrophy: A prospective multicentre study

The field of translational research in Duchenne muscular dystrophy (DMD) has been transformed in the last decade by a number of therapeutic targets, mostly studied in ambulant patients. A paucity of studies focus on measures that capture the non-ambulant stage of the disease, and the transition between the ambulant and non-ambulant phase. In this prospective natural history study, we report the results of a comprehensive assessment of respiratory, upper limb function and upper limb muscle strength in a group of 89 DMD boys followed in 3 European countries, 81 receiving corticosteroids, spanning a wide age range (5-18 years) and functional abilities, from ambulant (n = 60) to non-ambulant (n = 29). Respiratory decline could be detected in the early ambulatory phase using Peak Expiratory Flow percentage predicted (PEF%), despite glucocorticoid use (mean annual decline: 4.08, 95% CI [-7.44,-0.72], p = 0.02 in ambulant; 4.81, 95% CI [-6.79,-2.82], p < 0.001 in non-ambulant). FVC% captured disease progression in non-ambulant DMD subjects, with an annual loss of 5.47% (95% CI [-6.48,-4.45], p < 0.001). Upper limb function measured with the Performance of Upper Limb (PUL 1.2) showed an annual loss of 4.13 points (95% CI [-4.79,3.47], p < 0.001) in the non-ambulant cohort. Measures of upper limb strength (MyoGrip and MyoPinch) showed a continuous decline independent of the ambulatory status, when reported as percentage predicted (grip force -5.51%, 95% CI [-6.54,-4.48], p < 0.001 in ambulant and a slower decline -2.86%; 95% CI -3.29,-2.43, p < 0.001, in non-ambulant; pinch force: -2.66%, 95% CI [-3.82,-1.51], p < 0.001 in ambulant and -2.23%, 95% CI [-2.92,-1.53], p < 0.001 in non-ambulant). Furthermore, we also explored the novel concept of a composite endpoint by combining respiratory, upper limb function and force domains: we were able to identify clear clinical progression in patients in whom an isolated measurement of only one of these domains failed to appreciate the yearly change. Our study contributes to the field of natural history of DMD, linking the ambulant and non-ambulant phases of the disease, and suggests that composite scores should be explored further.

Home-Based Monitoring of Pulmonary Function in Patients with Duchenne Muscular Dystroph

Background:

Loss of pulmonary function is a main cause of early morbidity and mortality in patients with Duchenne muscular dystrophy (DMD). Standard of care guidelines recommend regular assessment of pulmonary function by hospital-based spirometry to detect onset and monitor progression of pulmonary function decline.

Objective:

To assess the feasibility of home-based monitoring of pulmonary function by a hand-held device (HHD) in adolescent and adult patients with DMD over a period of 12 months.

Methods:

In the phase III randomized placebo-controlled DELOS trial in 10–18 year old DMD patients, peak expiratory flow (PEF) measurements were collected weekly at home by the patient (assisted by parent/caregiver) using a peak flow meter HHD. Adherence to the use of the HHD was assessed and 12-month changes in PEF as percent of predicted (PEF% p) for the idebenone (N = 31) and the placebo treatment groups (N = 33) from HHD-derived data were compared to results from hospital-based spirometry.

Results:

A total of 2689 individual HHD assessments were analysed. Overall adherence to the use of the HHD over the course of the 12-month study duration was good (75.9%, SD 21.5%) and PEF% p data obtained at the same day by HHD and standard spirometry correlated well (Spearman’s rho 0.80; p < 0.001). Several analysis methods of HHD-derived data for PEF% p consistently demonstrate that idebenone treatment slowed the decline in PEF% p compared to placebo, which supports the statistically significant difference in favour of idebenone for PEF% p measured by standard spirometry.

Conclusions:

This study demonstrates that home-based monitoring of pulmonary function in adolescent patients with DMD using a HHD is feasible, provides reliable data compared to hospital-based spirometry and is therefore suitable for use in clinical practice and for clinical trials.

Risk factors for falls among boys under 18 years with muscular dystrophy

PURPOSE

Studies have shown that children with muscular dystrophy are at increased risk for falls, however there is insufficient information about what predicts the first and subsequent events. The purpose of this study was to describe the experience of injury with emphasis on identifying risk factors for fall-related injuries.

METHODS

We studied 269 boys with muscular dystrophy describing their injury experience and identifying risk and protective factors associated with 281 non-simultaneous injuries and 127 falls that resulted in Emergency Department visits and/or inpatient hospitalization during the period 1998-2014. We used a Cox model to estimate the predictors of an initial fall and a zero-inflated Poisson model to identify the predictors for the number of falls.

RESULTS

Falls accounted for the greatest number of injury occurrences; The most frequent injury type was contusion. The factors that were protective for falls were steroid use, wheelchair use, or having a heart condition. Baseline age was negatively associated with the risk of having any fall, but not significantly related to subsequent falls.

CONCLUSION

Wheelchair use and heart conditions associated with reduced risk of falls likely reflects decreased mobility. Clinicians should help families identify factors associated with falls among those who remain ambulatory.

Respiratory Management of the Patient With Duchenne Muscular Dystrophy

In 2010, Care Considerations for Duchenne Muscular Dystrophy, sponsored by the Centers for Disease Control and Prevention, was published in Lancet Neurology, and in 2018, these guidelines were updated. Since the publication of the first set of guidelines, survival of individuals with Duchenne muscular dystrophy has increased. With contemporary medical management, survival often extends into the fourth decade of life and beyond. Effective transition of respiratory care from pediatric to adult medicine is vital to optimize patient safety, prognosis, and quality of life. With genetic and other emerging drug therapies in development, standardization of care is necessary to accurately assess treatment effects in clinical trials. This revision of respiratory recommendations preserves a fundamental strength of the original guidelines: namely, reliance on a limited number of respiratory tests to guide patient assessment and management. A progressive therapeutic strategy is presented that includes lung volume recruitment, assisted coughing, and assisted ventilation (initially nocturnally, with the subsequent addition of daytime ventilation for progressive respiratory failure). This revision also stresses the need for serial monitoring of respiratory muscle strength to characterize an individual's respiratory phenotype of severity as well as provide baseline assessments for clinical trials. Clinical controversies and emerging areas are included.

Measures of respiratory inductance plethysmography (RIP) in children with neuromuscular disease

BACKGROUND

Pulmonary function testing (PFT) is essential for the clinical assessment of respiratory problems. Respiratory inductance plethysmography (RIP) is a non-invasive method of PFT requiring minimal patient cooperation. RIP measures the volumetric change in the ribcage and abdomen, from which work of breathing (WOB) indices are derived. WOB indices include: phase angle (Ф), percent ribcage (RC%), respiratory rate (RR), and labored breathing index (LBI). Heart rate (HR) is collected separately.

AIM

The goal of this study was to assess the utility of a newly developed RIP system, the pneuRIP, in an outpatient clinic setting in children with neuromuscular (NM) disease.

METHOD

The pneuRIP system measures and displays the WOB indices in real-time on an iPad display. Forty-three subjects, 22 NM patients and 21 healthy children (ages: 5-18 years) were enrolled.

RESULTS

Patients' means showed an increase of 119.8% for Ф, 15.7% for LBI, and 19.9% for HR compared with healthy subjects, when adjusted for age and gender. The study found significant differences between the mean values of the healthy subjects and patients in Ф (P = 0.000), LBI (P = 0.001), and HR (P = 0.001). No differences were noted for RC% and RR between groups. Data for Ф in NM patients were diffusely distributed as compared with healthy subjects based on analysis of histograms.

CONCLUSION

Non-invasive pneuRIP testing provided instantaneous PFT results. As compared to healthy subjects, NM patients showed abnormal results with increased markers of thoracoabdominal asynchrony, WOB indices, and biphasic breathing patterns likely resulting from NM weakness.

Long-Term Pulmonary Function in Duchenne Muscular Dystrophy: Comparison of Eteplirsen-Treated Patients to Natural History

Background:

Duchenne muscular dystrophy (DMD) is a rare, degenerative, X-linked genetic disease that results in progressive muscle loss and premature death, most commonly from respiratory or cardiac failure. DMD is primarily caused by whole exon deletions, resulting in a shift of the dystrophin mRNA reading frame that prevents production of functional dystrophin protein. Eteplirsen, a phosphorodiamidate morpholino oligomer (PMO), is designed to skip exon 51, restore the reading frame, and induce production of internally shortened dystrophin in patients with mutations amenable to such treatment.

Objective:

Describe lung function assessed throughout eteplirsen studies 201/202.

Methods:

Studies 201/202 included 12 patients treated with eteplirsen over 5 years. Pulmonary function tests included forced vital capacity (FVC), maximum expiratory pressure (MEP), and maximum inspiratory pressure (MIP). With no long-term placebo control, FVC results were compared with data from the United Dystrophinopathy Project (UDP). MIP and MEP were compared to published natural history.

Results:

Age-adjusted mixed-model repeated-measures analysis showed decreases of 2.3% and 2.6% annually for FVC% p and MEP% p, and an annual increase of 0.6% for MIP% p for the eteplirsen-treated cohort. Data from the UDP demonstrated a 4.1% decline in FVC% p. The published natural history reports annual declines of at least 2.7% and 3.8% for MEP% p and MIP% p, respectively, in patients with DMD.

Conclusions:

With eteplirsen treatment, deterioration of respiratory muscle function based on FVC% p was half of that seen in the UDP; MEP% p and MIP% p compared favorably with natural history.

Efficacy of Idebenone to Preserve Respiratory Function above Clinically Meaningful Thresholds for Forced Vital Capacity (FVC) in Patients with Duchenne Muscular Dystrophy

BACKGROUND

Patients with DMD experience progressive restrictive respiratory disease and eventual respiratory failure. Standard of care guidelines command changes in disease management when forced vital capacity percent of predicted (FVC% p) falls below clinically relevant thresholds. The Phase 3 DELOS trial in patients with DMD demonstrated that idebenone reduces the loss of peak expiratory flow and FVC compared to placebo (Buyse GM, et al.; Lancet 2015; 385 : 1748-57).

OBJECTIVE

Post-hoc analyses were conducted to assess whether treatment with idebenone could reduce the risk of patients dropping below clinically meaningful thresholds of FVC% p.

METHODS

The DELOS trial enrolled DMD patients 10-18 years of age not using glucocorticoids to receive idebenone (N = 31) or placebo (N = 33) for 12 months. Change from baseline in FVC and FVC% p was assessed by hospital spirometry and analyzed by mixed model of repeated measures and slope analysis and proportions of patients falling below clinically meaningful thresholds of FVC% p were compared.

RESULTS

The change over 1 year in FVC and FVC% p showed a consistent pattern in favor of idebenone treatment across multiple analysis methods and fewer patients in the idebenone group declined by a margin of 10% or more in FVC and FVC% p compared to placebo. There were also fewer patients in the idebenone group (15%) with a decline below FVC% p of 50% compared to the placebo group (25%) and fewer patients in the idebenone group (28%) showed a decline below FVC% p of 50% or 40% or 30% compared to the placebo group (43%).

CONCLUSIONS

These data added to the consistency and clinical meaningfulness of findings from the DELOS trial showing that idebenone can slow the loss of pulmonary function in patients with DMD.