The 6-minute walk test and other clinical endpoints in duchenne muscular dystrophy: reliability, concurrent validity, and minimal clinically important differences from a multicenter study

Wrist flexion and extension torques measured by highly sensitive dynamometer in healthy subjects from 5 to 80 years

BACKGROUND

Wrist movements become impaired with disease progression in various neuromuscular disorders. With the development of new therapies, thorough measurement of muscle strength is crucial to document natural disease progression and to assess treatment efficacy. We developed a new dynamometer enabling wrist flexion and extension torque measurement with high sensitivity. The aims of the present study were to collect norms for healthy children and adults, to compute predictive equations, to assess the reliability of the measurements and to test the feasibility of using the device in patients with a neuromuscular disease.

METHODS

The peak isometric torque of wrist flexion and extension was measured with the MyoWrist dynamometer in 345 healthy subjects aged between 5 and 80 years old and in 9 patients with limb girdle muscle dystrophy type 2 C (LGMD2C) aged between 16 and 38 years old.

RESULTS

Predictive equations are proposed for the wrist flexion and extension strength in children and adults. Intra-rater and inter-rater reliability was good with ICCs higher than 0.9 for both wrist flexion and extension. However, retest values were significantly higher by 4% than test results. The dynamometer was applied with no difficulty to patients with LGMD2C and was sensitive enough to detect strength as weak as 0.82 N.m. From our models, we quantified the mean strength of wrist extension in LGMD2C patients to 39 ± 17% of their predicted values.

CONCLUSIONS

The MyoWrist dynamometer provides reliable and sensitive measurement of both wrist flexion and extension torques. However, a training session is recommended before starting a study as a small but significant learning effect was observed. Strength deficit can be quantified from predictive equations that were computed from norms of healthy children and adults.

Effects of AFO use on walking in boys with Duchenne muscular dystrophy: a pilot study

PURPOSE

Although bracing in the late ambulatory stage of Duchenne muscular dystrophy (DMD) has been described, the effects of ankle-foot orthoses (AFOs) in earlier stages have not been evaluated. The aim of this pilot study was to describe the effects of dynamic response AFO (DR-AFO) use in boys with DMD who are ambulatory.

METHODS

Using a crossover design, 3 boys were randomly assigned to either a 2-week DR-AFO or a placebo intervention. Phases were separated by a 1-week washout period. Primary outcomes were time to walk 10 m and a 6-Minute Walk Test.

RESULTS

With DR-AFO use, declines in 10-m walk time (median decline = 0.8 s) and 6-Minute Walk Distance (median = 25.0 m) occurred. Parental report suggested that the use of DR-AFOs increased falls in 2 of 3 participants.

CONCLUSION

This pilot study does not support the use of DR-AFOs by boys with DMD who are ambulatory.

Inter-session reliability of electrical impedance myography in children in a clinical trial setting

OBJECTIVE

High reliability is a prerequisite for any test to be useful as a biomarker in a clinical trial. Here we assessed the reproducibility of electrical impedance myography (EIM) in children by comparing data obtained by different evaluators on separate days.

METHODS

Healthy boys and boys with Duchenne muscular dystrophy (DMD) aged 2-14 years underwent EIM of multiple muscles performed by two evaluators on two visits separated by 3-7 days. Single and multifrequency data were analyzed. Reliability was assessed via calculation of the percent relative standard deviation (% RSD), Bland-Altman analysis, and the intraclass correlation coefficient (ICC).

RESULTS

For both individual muscle data and data averaged across muscles, intra-evaluator measurements showed high repeatability for both 50 kHz phase and 50/200 kHz phase ratio values, with ICCs generally above 0.90 and % RSD below 10%. Inter-evaluator results showed very similar ICC and % RSD values as those obtained by the same evaluator.

CONCLUSIONS

Both the 50 kHz phase and 50/200 kHz phase ratio are reliable measures both across time and evaluators and in both health and disease.

SIGNIFICANCE

These results support the concept that EIM can serve as a reliable measure in clinical therapeutic trials in a pediatric population.

Reachable workspace in facioscapulohumeral muscular dystrophy (FSHD) by Kinect

INTRODUCTION

A depth-ranging sensor (Kinect) based upper extremity motion analysis system was applied to determine the spectrum of reachable workspace encountered in facioscapulohumeral muscular dystrophy (FSHD).

METHODS

Reachable workspaces were obtained from 22 individuals with FSHD and 24 age- and height-matched healthy controls. To allow comparison, total and quadrant reachable workspace relative surface areas (RSAs) were obtained by normalizing the acquired reachable workspace by each individual's arm length.

RESULTS

Significantly contracted reachable workspace and reduced RSAs were noted for the FSHD cohort compared with controls (0.473 ± 0.188 vs. 0.747 ± 0.082; P < 0.0001). With worsening upper extremity function as categorized by the FSHD evaluation subscale II + III, the upper quadrant RSAs decreased progressively, while the lower quadrant RSAs were relatively preserved. There were no side-to-side differences in reachable workspace based on hand-dominance.

CONCLUSIONS

This study demonstrates the feasibility and potential of using an innovative Kinect-based reachable workspace outcome measure in FSHD.

Gene therapy for muscular dystrophy: moving the field forward

Gene therapy for the muscular dystrophies has evolved as a promising treatment for this progressive group of disorders. Although corticosteroids and/or supportive treatments remain the standard of care for Duchenne muscular dystrophy, loss of ambulation, respiratory failure, and compromised cardiac function is the inevitable outcome. Recent developments in genetically mediated therapies have allowed for personalized treatments that strategically target individual muscular dystrophy subtypes based on disease pathomechanism and phenotype. In this review, we highlight the therapeutic progress with emphasis on evolving preclinical data and our own experience in completed clinical trials and others currently underway. We also discuss the lessons we have learned along the way and the strategies developed to overcome limitations and obstacles in this field.

The 6 minute walk test and performance of upper limb in ambulant duchenne muscular dystrophy boys

The Performance of Upper Limb (PUL) test was specifically developed for the assessment of upper limbs in Duchenne muscular dystrophy (DMD). The first published data have shown that early signs of involvement can also be found in ambulant DMD boys. The aim of this longitudinal Italian multicentric study was to evaluate the correlation between the 6 Minute Walk Test (6MWT) and the PUL in ambulant DMD boys. Both 6MWT and PUL were administered to 164 ambulant DMD boys of age between 5.0 and 16.17 years (mean 8.82). The 6 minute walk distance (6MWD) ranged between 118 and 557 (mean: 376.38, SD: 90.59). The PUL total scores ranged between 52 and 74 (mean: 70.74, SD: 4.66). The correlation between the two measures was 0.499. The scores on the PUL largely reflect the overall impairment observed on the 6MWT but the correlation was not linear. The use of the PUL appeared to be less relevant in the very strong patients with 6MWD above 400 meters, who, with few exceptions had near full scores. In patients with lower 6MWD the severity of upper limb involvement was more variable and could not always be predicted by the 6MWD value or by the use of steroids. Our results confirm that upper limb involvement can already be found in DMD boys even in the ambulant phase.

Safety and efficacy of drisapersen for the treatment of Duchenne muscular dystrophy (DEMAND II): an exploratory, randomised, placebo-controlled phase 2 study

BACKGROUND

Duchenne muscular dystrophy is caused by dystrophin deficiency and muscle deterioration and preferentially affects boys. Antisense-oligonucleotide-induced exon skipping allows synthesis of partially functional dystrophin. We investigated the efficacy and safety of drisapersen, a 2'-O-methyl-phosphorothioate antisense oligonucleotide, given for 48 weeks.

METHODS

In this exploratory, double-blind, placebo-controlled study we recruited male patients (≥5 years of age; time to rise from floor ≤7 s) with Duchenne muscular dystrophy from 13 specialist centres in nine countries between Sept 1, 2010, and Sept 12, 2012. By use of a computer-generated randomisation sequence, we randomly allocated patients (2:2:1:1; block size of six; no stratification) to drisapersen 6 mg/kg or placebo, each given subcutaneously and either continuously (once weekly) or intermittently (nine doses over 10 weeks). The primary endpoint was change in 6-min walk distance (6MWD) at week 25 in patients in the intention-to-treat population for whom data were available. Safety assessments included renal, hepatic, and haematological monitoring and recording of adverse events. This trial is registered with ClinicalTrials.gov, number NCT01153932.

FINDINGS

We recruited 53 patients: 18 were given continuous drisapersen, 17 were given intermittent drisapersen, and 18 were given placebo (continuous and intermittent groups combined). At week 25, mean 6MWD had increased by 31·5 m (SE 9·8) from baseline for continuous drisapersen, with a mean difference in change from baseline of 35·09 m (95% CI 7·59 to 62·60; p=0·014) versus placebo. We recorded no difference in 6MWD changes from baseline between intermittent drisapersen (mean change -0·1 [SE 10·3]) and placebo (mean difference 3·51 m [-24·34 to 31·35]) at week 25. The most common adverse events in drisapersen-treated patients were injection-site reactions (14 patients given continuous drisapersen, 15 patients given intermittent drisapersen, and six given placebo) and renal events (13 for continuous drisapersen, 12 for intermittent drisapersen, and seven for placebo), most of which were subclinical proteinuria. None of the serious adverse events reported (one for continuous, two for intermittent, and two for placebo) resulted in withdrawal from the study.

INTERPRETATION

Continuous drisapersen resulted in some benefit in 6MWD versus placebo at week 25. The safety findings are similar to those from previous studies. Ambulation improvements in this young population with early-stage Duchenne muscular dystrophy are encouraging but need to be confirmed in larger studies.

FUNDING

GlaxoSmithKline, Prosensa Therapeutics BV (a subsidiary of Prosensa Holding NV).

Gait energy expenditure in children with Duchenne muscular dystrophy: case study

This case study aimed to verify the model of Rose et al.1 as a feasible to assess energy expenditure in gait of children with Duchenne muscular dystrophy (DMD). Three DMD patients aged 6, 7 and 8 years old participated of this study. It was obtained weight, height, leg length measurement (LLM), resting and gait heart rate (HR) held on as 55-meter oval circuit performed during a two-minute test at each speed. Energy expenditure was calculated using the HR. It was performed a descriptive analysis (average) and these were compared, individually, to normative data. The average gait speed of these three patients was similar to the normative data for slow speed and lower considering comfortable and fast speed. The energy expenditure to slow speed of the patients 2 and 3 was similar to the normality, and lowest for patient 1; at comfortable speed, the energy expenditure obtained for all patients was similar; at fast speed, the patients 1 and 2 presented similar to normal values, but the patient 3 presented higher energy expenditure. It was concluded that the energy expenditure evaluation using HR was easily executed in the clinical practice and it can help therapeutic choices. For patient 3, an aerobic training could be indicated and for the others, they could keep the routine assessments.

Therapy of Genetic Disorders-Novel Therapies for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is an inherited, progressive muscle wasting disorder caused by mutations in the dystrophin gene. An increasing variety of approaches are moving towards clinical testing that all aim to restore dystrophin production and to enhance or preserve muscle mass. Gene therapy methods are being developed to replace the defective dystrophin gene or induce dystrophin production from mutant genes. Stem cell approaches are being developed to replace lost muscle cells while also bringing in new dystrophin genes. This review summarizes recent progress in the field with an emphasis on clinical applications.

The 6-Minute Walk Test and Person-Reported Outcomes in Boys with Duchenne Muscular Dystrophy and Typically Developing Controls: Longitudinal Comparisons and Clinically-Meaningful Changes Over One Year

Introduction: Data is currently lacking anchoring a 30-meter longitudinal change in walking ability by 6-minute walk test (6MWT) in Duchenne muscular dystrophy as a minimal clinically important difference and “clinically meaningful” person-reported outcomes (PROs) at differing levels of ambulatory ability. Methods: We describe correlation between measures, 1-year change in measures, and correlation of 1-year changes between measures for the six-minute walk test (6MWT), 10-meter run/walk velocity, PedsQL and POSNA Pediatric Outcomes Data Collection Instrument (PODCI) in 24 4-12 year old. ambulatory DMD and 36 typical controls, and determine if minimal clinically important differences (MCID) of PROs contribute to different estimates of 6-minute walk distance (6MWD) change at differing levels of ability. Results: PedsQL total and physical function and PODCI global, transfer/mobility and sports/physical function PROs demonstrated significant differences between DMD and controls (p<0.00001). In DMD, 6MWD and 10-meter run/walk velocity were correlated with PODCI domain scores, with the transfer/mobility scale showing the strongest relationship (r=0.79 and r=0.76). In DMD, 6MWD distance and 10-meter run/walk velocity weakly correlated with PedsQL domain scores. In DMD, 6MWD, 10-meter run/walk velocity, and PODCI global and transfer and basic mobility demonstrated significant one-year change and exceeded the amount of change representing MCID. In DMD, 6MWD change highly correlated with change in PODCI global and PODCI transfer/mobility scores (r=0.76 and r=0.93). PODCI global and PODCI transfer/mobility scales provided the best estimates of 6MWT performance. A “meaningful” 4.5 point change in a low PODCI transfer / basic mobility score of 30 to 34.5 was associated with a 5.6m 6MWD change from 150.3 to 155.9m. At PODCI levels closer to normative levels for healthy controls, the change in 6MWD distance associated with a “meaningful” change in PODCI scores was almost 46m. Discussion: At lower levels of function, smaller increases in 6MWD result in meaningful change in quality of life (QoL) instrument scores. At higher levels of function, larger increases may be necessary to achieve the same QoL change score.

The 6-minute walk test and other endpoints in Duchenne muscular dystrophy: longitudinal natural history observations over 48 weeks from a multicenter study

Introduction: Duchenne muscular dystrophy (DMD) subjects ≥5 years with nonsense mutations were followed for 48 weeks in a multicenter, randomized, double-blind, placebo-controlled trial of ataluren. Placebo arm data (N = 57) provided insight into the natural history of the 6-minute walk test (6MWT) and other endpoints. Methods: Evaluations performed every 6 weeks included the 6-minute walk distance (6MWD), timed function tests (TFTs), and quantitative strength using hand-held myometry. Results: Baseline age (≥7 years), 6MWD, and selected TFT performance are strong predictors of decline in ambulation (Δ6MWD) and time to 10% worsening in 6MWD. A baseline 6MWD of <350 meters was associated with greater functional decline, and loss of ambulation was only seen in those with baseline 6MWD <325 meters. Only 1 of 42 (2.3%) subjects able to stand from supine lost ambulation. Conclusion: Findings confirm the clinical meaningfulness of the 6MWD as the most accepted primary clinical endpoint in ambulatory DMD trials.