Leg muscle function and fatigue during walking in spinal muscular atrophy type 3

Beyond Contractures in Spinal Muscular Atrophy: Identifying Lower-Limb Joint Hypermobility

Background: The natural history of spinal muscular atrophy (SMA) is well understood, with progressive muscle weakness resulting in declines in function. The development of contractures is common and negatively impacts function. Clinically, joint hypermobility (JH) is observed but is poorly described, and its relationship with function is unknown. Methods: Lower-limb ROM (range of motion) assessments of extension and flexion at the hip, knee, and ankle were performed. ROMs exceeding the published norms were included in the analysis. The functional assessments performed included the six-minute walk test (6 MWT) and the Hammersmith Functional Motor Scale-Expanded (HFMSE). Results: Of the 143 participants, 86% (n = 123) had at least one ROM measure that was hypermobile, and 22% (n = 32) had three or more. The HFMSE scores were inversely correlated with hip extension JH (r = -0.60, p = 0.21; n = 6) and positively correlated with knee flexion JH (r = 0.24, p = 0.02, n = 89). There was a moderate, inverse relationship between the 6 MWT distance and ankle plantar flexion JH (r = -0.73, p = 0.002; n = 15). Conclusions: JH was identified in nearly all participants in at least one joint in this study. Hip extension, knee flexion and ankle plantar flexion JH was associated with function. A further understanding of the trajectory of lower-limb joint ROM is needed to improve future rehabilitation strategies.

Walking test outcomes in adults with genetic neuromuscular diseases: a systematic literature review of their measurement properties

INTRODUCTION

Neuromuscular diseases (NMDs) include a large group of heterogeneous diseases. NMDs frequently involve gait disorders, which affect quality of life. Several walking tests and tools have been described in the literature, but there is no consensus regarding the use of walking tests and tools in NMDs or of their measurement properties for walking outcomes. The aim of this review is to present an overview of walking tests, including their measurement properties when used in adults with inherited or genetic NMDs. The aim is to help clinicians and researchers choose the most appropriate test for their objective.

EVIDENCE ACQUISITION

A systematic review was conducted after consulting MEDLINE (via PubMed), EMBASE, Science direct, Google Scholar and Cochrane Central Register of Controlled Trials databases for published studies in which walking outcome measurement properties were assessed. The validity, reliability, measurement error and responsiveness properties were evaluated in terms of statistical methods and methodological design qualities using the COnsensus-based Standards for the selection of health Measurement Instruments (COSMIN) guidelines.

EVIDENCE SYNTHESIS

We included 46 studies in NMDs. These studies included 15 different walking tests and a wide variety of walking outcomes, assessed with six types of walking tools. Overall, the 6MWT was the most studied test in terms of measurement properties. The methodological design and statistical methods of most studies evaluating construct validity, reliability and measurement error were "very good." The majority of outcome measurements were valid and reliable. However, studies on responsiveness as minimal important difference or minimal important change were lacking or were found to have inadequate methodological and statistical methods according to the COSMIN guidelines.

CONCLUSIONS

Most walking outcomes were found to be valid and reliable in NMDs. However, in view of the growing number of clinical trials, further studies are needed to clarify additional measurement properties.

Measuring Fatigue and Fatigability in Spinal Muscular Atrophy (SMA): Challenges and Opportunities

Fatigue, a common symptom, together with the characteristic of performance fatigability, are well-documented features of SMA that impact quality of life and function. Importantly, establishing associations between multidimensional self-reported fatigue scales and patient performance has proven difficult. This review was conducted to evaluate the various patient-reported fatigue scales applied in SMA, with the objective of considering the limitations and advantages of each measure. Variable use of fatigue-related nomenclature, including conflicting terminology interpretation, has affected assessment of physical fatigue attributes, specifically perceived fatigability. This review encourages the development of original patient-reported scales to enable perceived fatigability assessment, providing a potential complementary method of evaluating treatment response.

Clinical and Research Readiness for Spinal Muscular Atrophy: The Time Is Now for Knowledge Translation

Disease-modifying therapies for spinal muscular atrophy (SMA) are rapidly changing the outlook for many individuals by substantially altering the clinical course, phenotypic expression, and functional outcomes. Physical therapists have played critical roles in the effective conduct and execution of clinical trials leading to the approval of these therapies. Given the treatment landscape, educating practicing clinicians to understand best practice is of great importance, and a timely call to action to facilitate knowledge translation from SMA researchers to clinicians is necessary. The SMA Clinical Trial Readiness Program engaged clinical and research centers, identified physical therapy knowledge gaps related to evaluation and outcomes assessment, and provided educational resources, including the development of a SMA Best Practices Clinical Evaluator Toolkit. Toolkit content synthesizes evidence and covers a breadth of issues relevant to practice, including background on SMA and the drug pipeline; therapist roles and responsibilities related to research; clinical and research evaluation; and useful materials and resources for additional education, training, and professional development. Surveys and telephone interviews were conducted with physical therapists managing individuals with SMA to determine their SMA practice experience and educational needs. Their recommendations, along with synthesized SMA research evidence, provided input into toolkit content development and assisted in identifying gaps important to address. Impact was assessed over time via utilization feedback surveys downloaded by clinicians across various settings. Open-ended feedback supported beneficial use of the toolkit for clinicians and researchers working with individuals with SMA. Next steps should include timely dissemination to bring this resource and others into practice in a systematic, efficacious, and engaging manner. As the treatment landscape for SMA evolves, the therapist's role in multidisciplinary care and research is of great importance, and a call to action for the development, implementation, evaluation and reporting of informed knowledge using evidence-based knowledge translation strategies is critical.

IMPACT

Partnership among patient advocacy groups, industry collaborators, and key opinion leaders/experts can optimize essential resource development to address the knowledge gap for best practices in physical therapy. This partnership model can be replicated for other diseases, providing an efficient way to support clinical trial readiness and target early development of evidence-based content and resources related to both research and best practice clinical evaluation for physical therapist researchers, clinicians, and patients. While identifying knowledge gaps and resource development are initial steps toward change in SMA practice, a rapidly changing rehabilitation outlook warrants a call to action for enhanced efforts aimed at improving rehabilitation evaluation, assessment, and care for this population. It is critical to forge a timely path forward for development, implementation, and sustainability of effective knowledge translation to practice for SMA.

Amifampridine safety and efficacy in spinal muscular atrophy ambulatory patients: a randomized, placebo-controlled, crossover phase 2 trial

Background

Spinal muscular atrophy (SMA) is an autosomal recessive disease where a deficient amount of SMN protein leads to progressive lower motor neuron degeneration. SMN-enhancing therapies are now available. Yet, fatigue and signs of impaired neuromuscular junction (NMJ) transmission could contribute to SMA phenotype. Amifampridine prolongs presynaptic NMJ terminal depolarization, enhancing neuromuscular transmission.

Methods

SMA-001 was a phase 2, 1:1 randomized, double-blind, placebo-controlled crossover study. Ambulatory (walking unaided at least 30 m) SMA Type 3 patients, untreated with SMN-enhancing medications, entered a run-in phase where amifampridine was titrated up to an optimized stable dose. Patients achieving at least three points improvement in Hammersmith Functional Motor Score Expanded (HFMSE) were randomized to amifampridine or placebo, alternatively, in the 28-day double-blind crossover phase. Safety was evaluated by adverse events (AE) collection. Primary efficacy measure was the HFMSE change from randomization. Secondary outcomes included timed tests and quality of life assessment. Descriptive analyses and a mixed effects linear model were used for statistics.

Results

From 14 January 2019, 13 patients, mean age 34.5 years (range 18–53), with 5/13 (38.5%) females, were included. No serious AE were reported. Transient paresthesia (33.3%) was the only amifampridine-related AE. Six patients for each treatment sequence were randomized. Amifampridine treatment led to a statistically significant improvement in HFMSE (mean difference 0.792; 95% CI from 0.22 to 1.37; p = 0.0083), compared to placebo, but not in secondary outcomes.

Discussion

SMA-001 study provided Class II evidence that amifampridine was safe and effective in treating ambulatory SMA type 3 patients. Clinical Trial Registration: NCT03781479; EUDRACT 2017-004,600-22.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00415-022-11231-7.

Systematic Review of Motor Function Scales and Patient-Reported Outcomes in Spinal Muscular Atrophy

ABSTRACT

Spinal muscular atrophy is a heterogeneous disease that results in loss of motor function. In an evolving treatment landscape, establishing the suitability and limitations of existing motor function scales and patient-reported outcomes used to monitor patients with this disease is important. A systematic review was conducted to examine utility of motor function scales and patient-reported outcomes in evaluating patients with spinal muscular atrophy. Published literature was reviewed up to June 2021 with no start date restriction. Of the reports screened, 122 were deemed appropriate for inclusion and are discussed in this review (including 24 validation studies for motor function scales or patient-reported outcomes). Fifteen motor function scales and patient-reported outcomes were identified to be commonly used (≥5 studies), of which 11 had available validation assessments. Each instrument has its strengths and limitations. It is imperative that the patient population (e.g., age, mobility), goals of treatment, and outcomes or endpoints of interest be considered when selecting the appropriate motor function scales and patient-reported outcomes for clinical studies.

Motor Unit and Capillary Recruitment During Fatiguing Arm-Cycling Exercise in Spinal Muscular Atrophy Types 3 and 4

BACKGROUND

Exercise intolerance is an important impairment in patients with SMA, but little is known about the mechanisms underlying this symptom.

OBJECTIVE

To investigate if reduced motor unit- and capillary recruitment capacity in patients with SMA contribute to exercise intolerance.

METHODS

Adolescent and adult patients with SMA types 3 and 4 (n = 15) and age- and gender matched controls (n = 15) performed a maximal upper body exercise test. We applied respiratory gas analyses, non-invasive surface electromyography (sEMG) and continuous wave near-infrared spectroscopy (CW-NIRS) to study oxygen consumption, arm muscle motor unit- and capillary recruitment, respectively.

RESULTS

Maximal exercise duration was twofold lower (p <  0.001) and work of breathing and ventilation was 1.6- and 1.8-fold higher (p <  0.05) in patients compared to controls, respectively. Regarding motor unit recruitment, we found higher normalized RMS amplitude onset values of sEMG signals from all muscles and the increase in normalized RMS amplitudes was similar in the m. triceps brachii, m. brachioradialis and m. flexor digitorum in SMA compared to controls. Median frequency, onset values were similar in patients and controls. We found a similar decrease in median frequencies of sEMG recordings from the m. biceps brachii, a diminished decrease from the m. brachioradialis and m. flexor digitorum, but a larger decrease from the m. triceps brachii. With respect to capillary recruitment, CW-NIRS recordings in m. biceps brachii revealed dynamics that were both qualitatively and quantitatively similar in patients and controls.

CONCLUSION

We found no evidence for the contribution of motor unit- and capillary recruitment capacity of the upper arm muscles in adolescent and adult patients with SMA types 3 and 4 as primary limiting factors to premature fatigue during execution of a maximal arm-cycling task.

Technology-outcome measures in neuromuscular disorders: a systematic review

BACKGROUND

Portable and wearable devices can monitor a number of physical performances and have been lately applied to patients with neuromuscular disorders (NMD).

METHODS

We performed a systematic search of literature databases following PRISMA principles, including all studies reporting the use of technological devices for motor function assessment in NMDs from 2000 to 2021. We also summarized the evidence on measurement properties (validity, reliability, responsiveness) of the analyzed technological outcome measures.

RESULTS

One-hundred studies fulfilled the selection criteria, most of them published in the last ten years. We defined four categories that gathered similar technologies: gait analysis tools, for clinical assessment of pace and posture; continuous monitoring of physical activity with inertial sensors, that allow "unsupervised" activity assessment; upper limb evaluation tools, including Kinect-based outcome measures to assess the reachable workspace; and new muscle strength assessment tools, such as Myotools. Inertial sensors have the evident advantage of being applied in the "in-home" setting, which has become especially appealing with the Covid-19 pandemic, although poor evidence from psychometric property assessment and results of the analyzed studies may limit their research application. Both Kinect-based outcome measures and Myotools have been already validated in multicenter studies and different NMDs, showing excellent characteristics for application in clinical trials.

CONCLUSION

This overview is intended to raise awareness on the potential of the different TOMs in the neuromuscular field and be an informative source for the design of future clinical trials, particularly in the era of telemedicine.

Magnetic resonance reveals mitochondrial dysfunction and muscle remodelling in spinal muscular atrophy

Genetic therapy has changed the prognosis of hereditary proximal spinal muscular atrophy, although treatment efficacy has been variable. There is a clear need for deeper understanding of underlying causes of muscle weakness and exercise intolerance in patients with this disease to further optimize treatment strategies. Animal models suggest that in addition to motor neuron and associated musculature degeneration, intrinsic abnormalities of muscle itself including mitochondrial dysfunction contribute to the disease aetiology.

To test this hypothesis in patients, we conducted the first in vivo clinical investigation of muscle bioenergetics. We recruited 15 patients and 15 healthy age and gender-matched control subjects in this cross-sectional clinico-radiological study. MRI and ³¹P magnetic resonance spectroscopy, the modality of choice to interrogate muscle energetics and phenotypic fibre-type makeup, was performed of the proximal arm musculature in combination with fatiguing arm-cycling exercise and blood lactate testing. We derived bioenergetic parameter estimates including: blood lactate, intramuscular pH and inorganic phosphate accumulation during exercise, and muscle dynamic recovery constants. A linear correlation was used to test for associations between muscle morphological and bioenergetic parameters and clinico-functional measures of muscle weakness.

MRI showed significant atrophy of triceps but not biceps muscles in patients. Maximal voluntary contraction force normalized to muscle cross-sectional area for both arm muscles was 1.4-fold lower in patients than in controls, indicating altered intrinsic muscle properties other than atrophy contributed to muscle weakness in this cohort. In vivo³¹P magnetic resonance spectroscopy identified white-to-red remodelling of residual proximal arm musculature in patients on the basis of altered intramuscular inorganic phosphate accumulation during arm-cycling in red versus white and intermediate myofibres. Blood lactate rise during arm-cycling was blunted in patients and correlated with muscle weakness and phenotypic muscle makeup. Post-exercise metabolic recovery was slower in residual intramuscular white myofibres in patients demonstrating mitochondrial ATP synthetic dysfunction in this particular fibre type.

This study provides the first in vivo evidence in patients that degeneration of motor neurons and associated musculature causing atrophy and muscle weakness in 5q spinal muscular atrophy type 3 and 4 is aggravated by disproportionate depletion of myofibres that contract fastest and strongest. Our finding of decreased mitochondrial ATP synthetic function selectively in residual white myofibres provides both a possible clue to understanding the apparent vulnerability of this particular fibre type in 5q spinal muscular atrophy types 3 and 4 as well as a new biomarker and target for therapy.

Clinical outcome assessments in Duchenne muscular dystrophy and spinal muscular atrophy: past, present and future

Scores and scales used in pediatric motor development for neuromuscular disorders have evolved greatly since the beginning of their development. In this review we provide a brief history of scales used in pediatric patients with neuromuscular disorders and an update regarding the advancement of the scales commonly used in patients with spinal muscular atrophy and Duchenne muscular dystrophy. We focus on the collaborative effort that has led to the development of outcomes and speak to the possible future of Clinical Outcome Assessments.

Neck and Trunk Muscle Strength in Children With Spinal Muscular Atrophy Is Lower Than in Healthy Controls and Depends on Disease Type

Background: Neck and trunk muscle strength and relationship with motor function in individuals with spinal muscular atrophy (SMA) is not investigated well. Information on maximum muscle strength that children with SMA may develop considerably expands the possibilities of assessing the effectiveness of pharmacological treatment methods and therapeutic procedures. This study sought to assess neck and trunk muscle strength in patients with SMA and to compare it with values noted in healthy children.

Methods: The study involved 56 individuals with SMA aged 5–16 not treated pharmacologically, including 9 patients with SMA type 1 (SMA1), 27 with SMA type 2 (SMA2), and 20 with SMA type 3 (SMA3). The control group included 111 healthy individuals aged 5–16. Neck and trunk muscle strength was assessed by means of a maximum voluntary isometric contraction method with the use of a handheld digital muscle tester MICROFET2. Moreover, relative strength was also calculated by standardising the maximum voluntary isometric contraction according to body mass. The Kruskal–Wallis test, Mann–Whitney U-test, and Spearman's rank correlation were used for statistical analysis.

Results: The reliability of the neck and trunk muscle strength measurements with the handheld digital muscle tester was excellent with ICC > 0.9. The values of muscle strength in SMA groups were significantly lower than in the control group. The values of relative torque of the neck muscles expressed in percentage values calculated with regard to the control group were at the level of 47.6–51.6% in SMA1 group, 54.8–58.1% in SMA2 group and 80.6–90.3% in SMA3 group. The percentage values for upper and lower trunk muscle strength were at the level of 42.6–68.4% in SMA1 group, 56.9–75.4% in SMA2 group and 76.7–94.8% in SMA3 group.

Conclusion: Handheld dynamometry provides reliable measures of neck and trunk muscle strength in SMA children. Neck and trunk muscle strength in children with SMA is lower than in healthy controls and depends on disease type, which confirms the theory based on clinical observations. Further, study is needed to investigate the effect of pharmacological treatment on the strength of the neck/trunk muscles, and relationship between neck and trunk muscle strength and motor capabilities.

Motor unit reserve capacity in spinal muscular atrophy during fatiguing endurance performance

OBJECTIVE

To investigate the availability of any motor unit reserve capacity during fatiguing endurance testing in patients with spinal muscular atrophy (SMA).

METHODS

We recorded surface electromyography (sEMG) of various muscles of upper- and lower extremities of 70 patients with SMA types 2-4 and 19 healthy controls performing endurance shuttle tests (ESTs) of arm and legs. We quantitatively evaluated the development of fatigability and motor unit recruitment using time courses of median frequencies and amplitudes of sEMG signals. Linear mixed effect statistical models were used to evaluate group differences in median frequency and normalized amplitude at onset and its time course.

RESULTS

Normalized sEMG amplitudes at onset of upper body ESTs were significantly higher in patients compared to controls, yet submaximal when related to maximal voluntary contractions, and showed an inverse correlation to SMA phenotype. sEMG median frequencies decreased and amplitudes increased in various muscles during execution of ESTs in patients and controls.

CONCLUSIONS

Decreasing median frequencies and increasing amplitudes reveal motor unit reserve capacity in individual SMA patients during ESTs at submaximal performance intensities.

SIGNIFICANCE

Preserving, if not expanding motor unit reserve capacity may present a potential therapeutic target in clinical care to reduce fatigability in individual patients with SMA.

Spinal muscular atrophy - insights and challenges in the treatment era

Spinal muscular atrophy (SMA) is an autosomal recessive motor neuron disease caused by deletion or mutation of SMN1. Four subtypes exist, characterized by different clinical severities. New therapeutic approaches have become available in the past few years, dramatically changing the natural history of all SMA subtypes, including substantial clinical improvement with the severe and advanced SMA type 1 variant. Trials have now demonstrated that phenotypic rescue is even more dramatic when pre-symptomatic patients are treated, and emerging real-world data are demonstrating the benefits of intervention even in the chronic phase of the condition. Here, we critically review how the field is rapidly evolving in response to the new therapies and questions that the new treatments have posed, including the effects of treatment at different ages and stages of disease, new phenotypes and long-term outcomes in patients who would not have survived without treatment, and decisions of who to treat and when. We also discuss how the outcomes associated with different timing of therapeutic intervention are contributing to our understanding of the biology and pathogenesis of SMA.

Neuroanatomical Models of Muscle Strength and Relationship to Ambulatory Function in Spinal Muscular Atrophy

BACKGROUND

Individuals with spinal muscular atrophy (SMA) III walk independently, but experience muscle weakness, gait impairments, and fatigue. Although SMA affects proximal more than distal muscles, the characteristic pattern of selective muscle weakness has not been explained. Two theories have been proposed: 1) location of spinal motor neurons; and 2) differences in segmental innervation.

OBJECTIVE

To identify neuroanatomical models that explain the selective muscle weakness in individuals with SMA and assess the relationship of these models to ambulatory function.

METHODS

Data from 23 ambulatory SMA participants (78.2% male), ages 10-56 years, enrolled in two clinical studies (NCT01166022, NCT02895789) were included. Strength was assessed using the Medical Research Council (MRC) score; ambulatory function was measured by distance walked on the 6-minute walk test (6 MWT). Three models were identified, and relationships assessed using Pearson correlation coefficients and linear regression.

RESULTS

All models demonstrated a positive association between strength and function, (p < 0.02). Linear regression revealed that Model 3B, consisting of muscles innervated by lower lumbar and sacral segments, explained 67% of the variability observed in 6 MWT performance (β= 0.670, p = 0.003).

CONCLUSIONS

Muscles innervated by lower lumbar and sacral segments, i.e. hip extensors, hip abductors, knee flexors and ankle dorsiflexors, correlated with and predicted greater ambulatory function. The neuroanatomical patterns of muscle weakness may contribute to a better understanding of disease mechanisms and enable delivery of targeted therapies.

Walking and weakness in children: a narrative review of gait and functional ambulation in paediatric neuromuscular disease

Background

Weakness is the primary impairment in paediatric neuromuscular diseases, impacting gait and gait-related functional activities in ambulant children affected by these rare and often degenerative diseases. Gait speed is an indicator of health and disability, yet gait is a complex, multi-faceted activity. Using the International Classification of Function, Health and Disability (ICF) model, assessment of gait and functional ambulation should consider the impairments, activity limitations and participation restrictions due to disease, and factors related to the environment and the individual person.

Methods

This narrative review involved a literature search of databases including Medline, Embase and Pubmed from 1946 to October 2019. Inclusion criteria included assessments of gait, endurance and ambulatory function in paediatric (0–18 years) neuromuscular diseases.

Results

Fifty-two papers were identified reporting assessments of gait speed, timed function, endurance and ambulatory capacity, gait-related balance and qualitative descriptive assessments of gait function and effect of disease on gait and gait-related activities. Gait speed is an indicator of disability and children with neuromuscular disease walk slower than typically developing peers. Increasing disease severity and age were associated with slower walking in children with Duchenne muscular dystrophy and Charcot-Marie-Tooth disease. The six-minute walk test is used widely as a test of endurance and ambulatory capacity; six-minute walk distance was substantially reduced across all paediatric neuromuscular diseases. Endurance and ambulatory capacity was more limited in children with spinal muscular atrophy type 3, congenital muscular dystrophy and older boys with Duchenne muscular dystrophy. Only a few papers considered normalisation of gait parameters accounting for the effect on gait of height in heterogeneous groups of children and linear growth in longitudinal studies. Balance related to gait was considered in five papers, mainly in children with Charcot-Marie-Tooth disease. There was limited investigation of factors including distance requirements and terrain in children’s typical environments and personal factors related to self-perception of disease effect on gait and gait-related function.

Conclusion

Assessments of gait and functional ambulation are important considerations in documenting disease progression and treatment efficacy in the clinical setting; and in clinical trials of disease-modifying agents and physiotherapeutic interventions in paediatric neuromuscular diseases. There is a need for expert consensus on core gait and functional ambulation assessments for use in clinical and research settings.

Nusinersen improves walking distance and reduces fatigue in later-onset spinal muscular atrophy

Introduction

Ambulatory individuals with spinal muscular atrophy (SMA) experience muscle weakness, gait impairments, and fatigue that affect their walking ability. Improvements have been observed in motor function in children treated with nusinersen, but its impact on fatigue has not been studied.

Methods

Post hoc analyses were used to examine changes in 6‐minute walk test (6MWT) distance and fatigue in children and adolescents with SMA type II and III who received their first dose of nusinersen in the phase Ib/IIa, open‐label CS2 study and were ambulatory during CS2 or the extension study, CS12.

Results

Fourteen children performed the 6MWT. Median (25th, 75th percentile) distance walked increased over time by 98.0 (62.0, 135.0) meters at day 1050, whereas median fatigue changed by −3.8% (−19.7%, 1.4%).

Discussion

These results support previous studies demonstrating clinically meaningful effects of nusinersen on motor function in children and adolescents with later‐onset SMA.

Assessment of fatigability in patients with spinal muscular atrophy: development and content validity of a set of endurance tests

BACKGROUND

Fatigability has emerged as an important dimension of physical impairment in patients with Spinal Muscular Atrophy (SMA). At present reliable and valid outcome measures for both mildly and severely affected patients are lacking. Therefore the primary aim of this study is the development of clinical outcome measures for fatigability in patients with SMA across the range of severity.

METHODS

We developed a set of endurance tests using five methodological steps as recommended by the 'COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN). In this iterative process, data from multiple sources were triangulated including a scoping review of scientific literature, input from a scientific and clinical multidisciplinary expert panel and three pilot studies including healthy persons (N = 9), paediatric patients with chronic disorders (N = 10) and patients with SMA (N = 15).

RESULTS

Fatigability in SMA was operationalised as the decline in physical performance. The following test criteria were established; one method of testing for patients with SMA type 2-4, a set of outcome measures that mimic daily life activities, a submaximal test protocol of repetitive activities over a longer period; external regulation of pace. The scoping review did not generate suitable outcome measures. We therefore adapted the Endurance Shuttle Walk Test for ambulatory patients and developed the Endurance Shuttle Box and Block Test and the - Nine Hole Peg Test for fatigability testing of proximal and distal arm function. Content validity was established through input from experts and patients. Pilot testing showed that the set of endurance tests are comprehensible, feasible and meet all predefined test criteria.

CONCLUSIONS

The development of this comprehensive set of endurance tests is a pivotal step to address fatigability in patients with SMA.

Ambulatory function in spinal muscular atrophy: Age-related patterns of progression

Individuals with spinal muscular atrophy (SMA) type 3 are able to walk but they have weakness, gait impairments and fatigue. Our primary study objective was to examine longitudinal changes in the six-minute walk test (6MWT) and to evaluate whether age and SMA type 3 subtype are associated with decline in ambulatory function. Data from three prospective natural history studies were used. Seventy-three participants who performed the 6MWT more than once, at least 6 months apart, were included; follow-up ranged from 0.5-9 years. Only data from patients who completed the 6MWT were included. The mean age of the participants was 13.5 years (range 2.6-49.1), with 52 having disease onset before age 3 years (type 3A). At baseline, type 3A participants walked a shorter distance on average (257.1 m) than type 3B participants (390.2 m) (difference = 133.1 m, 95% confidence interval [CI] 71.8-194.3, p < 0.001). Distance walked was weakly associated with age (r = 0.25, p = 0.04). Linear mixed effects models were used to estimate the mean annual rate of change. The overall mean rate of change was -7.8 m/year (95% CI -13.6 --2.0, p = 0.009) and this did not differ by subtype (type 3A: -8.5 m/year, type 3B: -6.6 m/year, p = 0.78), but it did differ by age group (< 6: 9.8 m/year; 6-10: -7.9 m/year; 11-19: -20.8 m/year; ≥ 20: -9.7 m/year; p = 0.005). Our results showed an overall decline on the 6MWT over time, but different trajectories were observed depending on age. Young ambulant SMA patients gain function but in adolescence, patients lose function. Future clinical trials in ambulant SMA patients should consider in their design the different trajectories of ambulatory function over time, based on age.

Feasibility of Using Microsoft Kinect to Assess Upper Limb Movement in Type III Spinal Muscular Atrophy Patients

Although functional rating scales are being used increasingly as primary outcome measures in spinal muscular atrophy (SMA), sensitive and objective assessment of early-stage disease progression and drug efficacy remains challenging. We have developed a game based on the Microsoft Kinect sensor, specifically designed to measure active upper limb movement. An explorative study was conducted to determine the feasibility of this new tool in 18 ambulant SMA type III patients and 19 age- and gender-matched healthy controls. Upper limb movement was analysed elaborately through derived features such as elbow flexion and extension angles, arm lifting angle, velocity and acceleration. No significant differences were found in the active range of motion between ambulant SMA type III patients and controls. Hand velocity was found to be different but further validation is necessary. This study presents an important step in the process of designing and handling digital biomarkers as complementary outcome measures for clinical trials.

Effect of the 6-minute walk test on plantar loading and capability to produce ankle plantar flexion forces

The six-minute walk test (6MWT) is used to evaluate the ambulatory capacity of patients suffering from respiratory disorders, obesity or neuromuscular diseases. Our primary aim was to evaluate the effects of the 6MWT on the postural sway and the ankle plantar flexion forces in healthy subjects. We measured the ankle plantar flexion forces and the plantar contact area before and after a 6MWT in normal weight and overweight subjects with no history of respiratory, cardiac, and neuromuscular disorders. A post-6MWT sensation of bodily fatigue was evaluated by Multidimensional Fatigue Inventory (MFI) and Pichot fatigue scales. A computerized pedobarographic platform was used to collect the mean plantar contact area, the changes of the center of pressure (CoP) surface and its medial and lateral deviations. In a limited number of subjects, the reproducibility of all the measurements was explored. In both groups, the 6MWT elicited a sensation of bodily fatigue. It also significantly reduced the ankle plantar flexion forces, and increased both the mean plantar contact area and the CoP surface, the changes being not apparent after 10min. The post-6MWT lateral CoP deviations were accentuated in normal weight subjects, while an increase in medial CoP deviations occurred in overweight ones. The 6MWT-induced changes in the plantar flexion force and pedobarographic variables were reproducible. Because this study clearly showed some post-6MWT alterations of the subjects' posture sway of our subjects, we questioned the possible mechanisms occurring that could explain the altered muscle force and the transient destabilization of posture after the 6MWT.

Six-minute walk test is reliable and valid in spinal muscular atrophy

INTRODUCTION

The Six-Minute Walk Test (6MWT) was adopted as a clinical outcome measure for ambulatory spinal muscular atrophy (SMA). However, a systematic review of measurement properties reported significant variation among chronic pediatric conditions. Our purpose was to assess the reliability/validity of the 6MWT in SMA.

METHODS

Thirty participants performed assessments, including the 6MWT, strength, and function. Reproducibility was evaluated by intraclass correlation coefficients. Criterion/convergent validity were determined using Pearson correlation coefficients.

RESULTS

Test-retest reliability was excellent. The 6MWT was associated positively with peak oxygen uptake, Hammersmith Functional Motor Scale Expanded (HFMSE), lower extremity manual muscle testing, knee flexion hand-held dynamometry, and inversely with 10-m walk/run. The 6MWT discriminates between disease severity, unlike the HFMSE.

CONCLUSIONS

This study documents measurement properties of reproducibility, positive criterion validity, and convergent validity with established clinical assessments and reaffirms the value of the 6MWT as a pivotal outcome measure in SMA clinical trials. Muscle Nerve 54: 836-842, 2016.

Resistance strength training exercise in children with spinal muscular atrophy

INTRODUCTION

Preliminary evidence in adults with spinal muscular atrophy (SMA) and in SMA animal models suggests exercise has potential benefits in improving or stabilizing muscle strength and motor function.

METHODS

We evaluated feasibility, safety, and effects on strength and motor function of a home-based, supervised progressive resistance strength training exercise program in children with SMA types II and III. Up to 14 bilateral proximal muscles were exercised 3 times weekly for 12 weeks.

RESULTS

Nine children with SMA, aged 10.4 ± 3.8 years, completed the resistance training exercise program. Ninety percent of visits occurred per protocol. Training sessions were pain-free (99.8%), and no study-related adverse events occurred. Trends in improved strength and motor function were observed.

CONCLUSIONS

A 12-week supervised, home-based, 3-day/week progressive resistance training exercise program is feasible, safe, and well tolerated in children with SMA. These findings can inform future studies of exercise in SMA.