Six-minute walk test versus two-minute walk test in children with Duchenne muscular dystrophy: Is more time more information?

Pig models for translational Duchenne muscular dystrophy research

Duchenne muscular dystrophy (DMD) is caused by mutations in the X-linked DMD gene, resulting in the absence of dystrophin, progressive muscle degeneration, and heart failure. Genetically tailored pig models resembling human DMD mutations recapitulate the biochemical, clinical, and pathological hallmarks of DMD with an accelerated disease progression compared to human patients. DMD pigs have been used to evaluate therapeutic concepts such as gene editing to reframe a disrupted DMD reading frame or the delivery of artificial chromosome vectors carrying the complete DMD gene. Moreover, DMD pigs have been instrumental in validating new diagnostic modalities such as multispectral optoacoustic tomography (MSOT) for non-invasive monitoring of disease progression. DMD pigs may thus help to bridge the gap between proof-of-concept studies in cellular or rodent models and clinical studies in patients.

Feasibility of a Child-Friendly 2-Minute Walk Test: A Crossover Randomized Controlled Trial

AIMS

Most studies that use the NIH Toolbox 2-Minute Walk Test with young children, modify the protocol, compromising the generalizability of outcomes. A standardizable protocol is needed. The purpose of this study was to compare the 2MWT performance of children ages 3-6 years on the standard NIH Toolbox protocol and on a modified protocol designed to support young children.

METHODS

Cross-over randomized controlled trial. Fifteen typically developing children ages 3-6 years were randomly assigned to the performance order of the NIH toolbox 2MWT protocol and the Modified Accessibility Path (MAP) 2MWT protocol. Outcome variables and statistical analyses included test completion (McNemar test), distance walked (Wilcoxon signed-rank test), and accuracy (general estimating equation model with Poisson distribution).

RESULTS

All children completed 2 min of walking with the MAP protocol. Only 40% of children completed the NIH Toolbox protocol, with 83% of these NIH completers bolstered by previous exposure to the MAP protocol. Collapsed across the order, children also had significantly fewer errors per lap with the MAP protocol (p < 0.0001), despite walking a significantly greater distance (p = 0.006).

CONCLUSIONS

These findings lend preliminary support for standardized application of a 2MWT with young children when the protocol is designed to be child-friendly.

Exercise testing to guide safe discharge from hospital in COVID-19: a scoping review to identify candidate tests

OBJECTIVES

We aimed to identify exercise tests that have been validated to support a safe discharge to home in patients with or without COVID-19.

STUDY DESIGN

Scoping review, using PRISMA-ScR reporting standards. Medline, PubMed, AMED, Embase, CINAHL and LitCovid databases were searched between 16 and 22 February 2021, with studies included from any publication date up to and including the search date.

INTERVENTION

Short exercise tests.

PRIMARY OUTCOME MEASURES

Safe discharge from hospital, readmission rate, length of hospital stay, mortality. Secondary outcomes measures: safety, feasibility and reliability.

RESULTS

Of 1612 original records screened, 19 studies were included in the analysis. These used a variety of exercise tests in patients with chronic obstructive pulmonary disease, suspected pulmonary embolism and pneumocystis carinii pneumonia, heart failure or critical illness. Only six studies had examined patients with COVID-19, of these two were still recruiting to evaluate the 1 min sit-to-stand test and the 40-steps test. There was heterogeneity in patient populations, tests used and outcome measures. Few exercise tests have been validated to support discharge decisions. There is currently no support for short exercise tests for triage of care in patients with COVID-19.

CONCLUSIONS

Further research is needed to aid clinical decision-making at discharge from hospital.

Multidimensional Biomechanics-Based Score to Assess Disease Progression in Duchenne Muscular Dystrophy

(1) Background: Duchenne (DMD) is a rare neuromuscular disease that progressively weakens muscles, which severely impairs gait capacity. The Six Minute-Walk Test (6MWT), which is commonly used to evaluate and monitor the disease's evolution, presents significant variability due to extrinsic factors such as patient motivation, fatigue, and learning effects. Therefore, there is a clear need for the establishment of precise clinical endpoints to measure patient mobility. (2) Methods: A novel score (6M+ and 2M+) is proposed, which is derived from the use of a new portable monitoring system capable of carrying out a complete gait analysis. The system includes several biomechanical sensors: a heart rate band, inertial measurement units, electromyography shorts, and plantar pressure insoles. The scores were obtained by processing the sensor signals and via gaussian-mixture clustering. (3) Results: The 6M+ and 2M+ scores were evaluated against the North Star Ambulatory Assessment (NSAA), the gold-standard for measuring DMD, and six- and two-minute distances. The 6M+ and 2M+ tests led to superior distances when tested against the NSAA. The 6M+ test and the 2M+ test in particular were the most correlated with age, suggesting that these scores better characterize the gait regressions in DMD. Additionally, the 2M+ test demonstrated an accuracy and stability similar to the 6M+ test. (4) Conclusions: The novel monitoring system described herein exhibited good usability with respect to functional testing in a clinical environment and demonstrated an improvement in the objectivity and reliability of monitoring the evolution of neuromuscular diseases.

The impact of genotype on outcomes in individuals with Duchenne muscular dystrophy: A systematic review

Duchenne muscular dystrophy (DMD) is associated with progressive muscle weakness, loss of ambulation (LOA), and early mortality. In this review we have synthesized published data on the clinical course of DMD by genotype. Using a systematic search implemented in Medline and Embase, 53 articles were identified that describe the clinical course of DMD, with pathogenic variants categorizable by exon skip or stop-codon readthrough amenability and outcomes presented by age. Outcomes described included those related to ambulatory, cardiac, pulmonary, or cognitive function. Estimates of the mean (95% confidence interval) age at LOA ranged from 9.1 (8.7-9.6) years among 90 patients amenable to skipping exon 53 to 11.5 (9.5-13.5) years among three patients amenable to skipping exon 8. Although function worsened with age, the impact of genotype was less clear for other outcomes (eg, forced vital capacity and left ventricular ejection fraction). Understanding the distribution of pathogenic variants is important for studies in DMD, as this research suggests major differences in the natural history of disease. In addition, specific details of the use of key medications, including corticosteroids, antisense oligonucleotides, and cardiac medications, should be reported.

Is Exercise-Induced Fatigue a Problem in Children with Duchenne Muscular Dystrophy?

OBJECTIVE

Duchenne muscular dystrophy (DMD) is a devastating X-linked muscular disorder. The number of studies investigating new therapeutic approaches is substantially increasing. This study aims to investigate the impact and diagnostic value of exercise-induced fatigue in DMD, which has been proposed as a suitable outcome parameter in other conditions like spinal muscular atrophy.

PATIENTS AND METHODS

A cohort of 55 DMD patients (49 of them treated with steroids and 9 with ataluren) underwent a total of 241 6MWT (mean 4.4 tests/patient) which were retrospectively analyzed. Exercise-induced fatigue was assessed by the ratio between the distance achieved in the sixth minute and the distance in the second minute of the 6MWT. In previous studies a quotient above 1 was defined as a sign of fatigue.

RESULTS

The average fatigue quotient in the whole cohort of patients was 1.0. In a further analysis no impact of age, steroid therapy, ataluren therapy, overall disability, and distance in the 6-minute walk test (6MWT) on fatigue in DMD patients could be shown.

CONCLUSION

Our data show that fatigue does not play a relevant role in DMD. Analysis of fatigue is not a useful outcome parameter in DMD studies. For this reason we suggest the 2MWT, which is better accepted by the patients, as an alternative to the commonly 6MWT.

Longitudinal functional and imaging outcome measures in FKRP limb-girdle muscular dystrophy

Background

Pathogenic variants in the FKRP gene cause impaired glycosylation of α-dystroglycan in muscle, producing a limb-girdle muscular dystrophy with cardiomyopathy. Despite advances in understanding the pathophysiology of FKRP-associated myopathies, clinical research in the limb-girdle muscular dystrophies has been limited by the lack of normative biomarker data to gauge disease progression.

Methods

Participants in a phase 2 clinical trial were evaluated over a 4-month, untreated lead-in period to evaluate repeatability and to obtain normative data for timed function tests, strength tests, pulmonary function, and body composition using DEXA and whole-body MRI. Novel deep learning algorithms were used to analyze MRI scans and quantify muscle, fat, and intramuscular fat infiltration in the thighs. T-tests and signed rank tests were used to assess changes in these outcome measures.

Results

Nineteen participants were observed during the lead-in period for this trial. No significant changes were noted in the strength, pulmonary function, or body composition outcome measures over the 4-month observation period. One timed function measure, the 4-stair climb, showed a statistically significant difference over the observation period. Quantitative estimates of muscle, fat, and intramuscular fat infiltration from whole-body MRI corresponded significantly with DEXA estimates of body composition, strength, and timed function measures.

Conclusions

We describe normative data and repeatability performance for multiple physical function measures in an adult FKRP muscular dystrophy population. Our analysis indicates that deep learning algorithms can be used to quantify healthy and dystrophic muscle seen on whole-body imaging.

Trial registration

This study was retrospectively registered in clinicaltrials.gov (NCT02841267) on July 22, 2016 and data supporting this study has been submitted to this registry.

Assessing manual dexterity: Comparing the WorkAbility Rate of Manipulation Test with the Minnesota Manual Dexterity Test

STUDY DESIGN

Cross-sectional study.

INTRODUCTION

The WorkAbility Rate of Manipulation Test (WRMT), an adaptation of the Minnesota Manual Dexterity Test (MMDT), contains a revised board and protocols to improve its utility for therapy or fitness assessment.

PURPOSE OF THE STUDY

To describe the development and preliminary psychometric properties of WRMT.

METHODS

Sixty-six healthy participants completed MMDT and WRMT in a random order followed by a user experience survey. We compared tests using repeated-measures analysis of variance, test-retest reliability, and examined agreement between tests.

RESULTS

Despite the similarities of these 2 instruments, the different administration protocols resulted in statistically different score distributions (P < .001). Results supported good test-retest reliability of WRMT (placing test ICC = 0.88-0.90 and turning test ICC = 0.68-0.82). The WRMT correlated moderately with MMDT (r = 0.81 in placing test and r = 0.44-0.57 in turning test). Bland-Altman plot showed that the differences in completion time were 3.8 seconds between placing tests and 19.6 (both hands), 0.3 (right hand), and 3.9 (left hand) seconds between turning tests. Overall, participants felt that the instruction of WRMT was easier to follow (44%) and preferred its setup, color, and depth of the test board (49%). Time required to complete 1 panel of 20 disks correlated highly with the time needed to finish a complete trial of 60 disks in both MMDT (r = 0.91-0.97) and WRMT (r = 0.88-0.95).

CONCLUSIONS

Caution is warranted in comparing scores from these 2 test variants.

LEVEL OF EVIDENCE

3b.

Two-minute versus 6-minute walk distances during 6-minute walk test in neuromuscular disease: Is the 2-minute walk test an effective alternative to a 6-minute walk test?

Functional tests such as Motor Function Measure-32 (MFM-32), supine to stand, ascend/descend stairs permit the assessment of task-specific motor function in neuromuscular disease (NMD). The 6-min walk test (6MWT), though functional, is primarily used to assess endurance and disease progression in children with neuromuscular disorders. Barriers to 6MWT administration, in this population, can include reduced attention span due to age and inability to tolerate test length due to weakness. We propose task-specific functional deficits are related to endurance. Additionally, the 2-min walk test (2MWT) could effectively replace the 6MWT in this population. Seventy-seven participants, ages 5-18, with a variety of neuromuscular disorders performed the 6MWT, timed functional tests (TFT), and the MFM-32. Correlation and paired t-test analyses were used to compare the distance walked in the first 2 min (2MWD) to the distance walked in the entire 6 min (6MWD) and to the functional outcome measures above. The 2MWD strongly correlated with 6MWD and the other outcome measures. Paired t-test analysis also showed that the 2MWD did not differ from the distance walked in the last 2 min of the 6MWT. Although equivalence testing could not reject the claim that this difference exceeded the upper practical limit of 9.5 m, it only showed a modest overestimation of the 4-6MWD compared with the 2MWD. Together, our results support the ability of the 2MWD to predict the 6MWD, specifically in the pediatric neuromuscular disease population.

The Use of a Wheelchair Propulsion Field Test to Determine Peak Heart Rate in Children and Adolescents With Myelomeningocele

PURPOSE

We analyzed the evolution and pattern of heart rate (HR) during the 12-minute wheelchair propulsion field test (WPFT) and compared the peak HR (HR_peak) from the WPFT to the HR_peak obtained in the progressive cardiopulmonary exercise test on arm cranking ergometer (ACT). We aimed to determine if the field test detects the HR_peak consistently and could be used in clinical practice.

METHODS

Eleven wheelchair-using children and adolescents with myelomeningocele (aged 8-15 y) performed a maximal ACT and a 12-minute WPFT. HR was recorded continuously at rest, during each minute of the tests, and at recovery. Mixed analysis of variance was used to compare the variables at rest and peak. Bland-Altman plot and Lin's concordance correlation coefficient were used to show agreement between the tests.

RESULTS

During minute 2 of the WPFT, participants reached 73%-96% of the HR_peak values recorded in the ACT. From minutes 4 to 12, participants reached HR_peak values ranging 86%-109% of the values recorded in the ACT. There is agreement between the ACT and the WPFT tests.

CONCLUSION

WPFT with minimal duration of 4 minutes may be an alternative tool to obtain HR_peak in children and adolescents with myelomeningocele.

Ankle-Foot Orthosis in Duchenne Muscular Dystrophy: A 4 year Experience in a Multidisciplinary Neuromuscular Disorders Clinic

OBJECTIVE

To assess Ankle-Foot-Orthosis (AFO) requirement and ambulation in Duchenne Muscular Dystrophy (DMD) patients seen over a period of 4 y at a multi-disciplinary Neuromuscular disorders clinic (NMD).

METHODS

A study was conducted in university quaternary research hospital with DMD patients confirmed by MLPA (multiplex ligation - dependent probe amplification) method and were evaluated between January 2012 and December 2015. Their ambulatory status, detailed neurological and functional status were recorded. Requirement of AFOs was determined and provided.

RESULTS

In total 126 DMD children reported to the NMD clinic. Mean age at presentation was 7.6 y (range 2 to12 y, SD 2.1). Mean duration of illness at first evaluation was 3.4 y (range 0.5 to 10 y, SD 2.0). AFO's were advised at a mean age of 8.5 y (range 7 to 12 y, SD 1.8). Fifty-nine patients were advised AFO as resting or walking splint. At last follow-up 113 patients were still ambulatory whereas 13 had become wheel chair bound. Out of 59 patients, 48 were still wearing AFOs and the remaining discontinued AFOs for various reasons.

CONCLUSIONS

Children with DMD require wearing of AFOs as resting or walking splint, mostly in first or early second decade of life. As there is some gap between onset of clinical signs and requirement of orthosis, follow-up preferably at a multidisciplinary clinic at regular intervals is desirable for timely intervention in the form of AFOs or other splints to prolong ambulatory status in these patients.