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.

Differential impact on motor unit characteristics across severities of adult spinal muscular atrophy

OBJECTIVE

To test the hypotheses that decomposition electromyography (dEMG) motor unit action potential (MUAP) amplitude and firing rate are altered in SMA; dEMG parameters are associated with strength and function; dEMG parameters are correlated with traditional electrophysiological assessments.

METHODS

Ambulatory and non-ambulatory adults with SMA on nusinersen and healthy controls were enrolled. MUAPs were decomposed from multielectrode surface recordings during 30-s maximum contraction of the abductor digiti minimi (ADM). Isometric strength, upper limb function, patient-reported function, and standard electrophysiologic measures of the ADM (compound muscle action potential [CMAP], single motor unit potential [SMUP], motor unit number estimation [MUNE]) were collected.

RESULTS

dEMG MUAP amplitudes were higher in ambulatory versus control and non-ambulatory groups and were higher in controls versus non-ambulatory SMA. In contrast, dEMG firing rates were higher in ambulatory versus non-ambulatory and control groups but similar between non-ambulatory and control. dEMG parameters showed moderate to strong positive correlation with strength and function whereas CMAP and MUNE better correlated with function than strength. SMUP did not correlate with strength, function, or dEMG MUAP amplitude. dEMG parameters show overall good test-retest reliability.

INTERPRETATION

dEMG provided reliable, noninvasive measure of MUAP amplitude size and firing rate and revealed divergent patterns across disease severity in adults with SMA. Firing rate enhancement, as seen in milder SMA, may provide a therapeutic avenue for improving function in more severe SMA, where firing rates appear preserved. MUAP amplitude size and firing rate, quantified with dEMG, may be promising monitoring biomarker candidates for noninvasive assessment of SMA.

Objective measurement of oral function in adults with spinal muscular atrophy

BACKGROUND

Impairment of bulbar function in adult individuals with spinal muscular atrophy (SMA) usually is not assessed by established motor scores. Measurements of oral function including quantitative muscle and endurance tests are able to detect subtle changes. The aim of this study was to systematically evaluate the measurement of maximum bite force and endurance, maximum tongue pressure and endurance, as well as maximum mouth opening in adult individuals with SMA types 2 and 3.

METHODS

Data from oral function tests in 43 individuals were analyzed. Differences in oral function between individuals with different SMA types and numbers of SMN2 copies were tested. Spearman´s rho correlations among oral function measures themselves as well as with established clinical outcome scales were analyzed.

RESULTS

The absolute maximum measures of oral function (maximum bite force, maximum tongue pressure, maximum mouth opening) were able to discriminate between individuals with different SMA types, individuals with a different number of SMN2 copies and with different walking abilities. The pairwise correlations of the absolute maximum measures of oral function were fair to moderate in size; the same was true for their correlations with the established motor scores. All correlations assessing endurance measures of oral function were weaker and statistically insignificant.

CONCLUSIONS

Among the oral function tests maximum tongue pressure and maximum mouth opening are particulary promising as clinical and sensitive outcome measures for clinical trials. Oral function tests may supplement existing motor scores, in particular concerning specific questions about bulbar function or in severely affected non-ambulatory individuals where mild (treatment-related) changes would otherwise remain undetected. Trial registration DRKS, DRKS00015842. Registered 30 July 2019, https://drks.de/search/de/trial/DRKS00015842.

Psychometric evaluation of modified spinal muscular atrophy functional rating scale (SMAFRS) in adult patients using Rasch analysis

INTRODUCTION/AIMS

The Spinal Muscular Atrophy Functional Rating Scale (SMAFRS) was first developed as a secondary functional outcome measure to detect changes over time in patients with spinal muscular atrophy (SMA) in clinical trials. Its modified version evaluates 10 activities of daily living. The aim of the study was to analyze modified SMAFRS data using item response theory psychometric models.

METHODS

A total of 253 responses from 41 adult patients with ambulatory and non-ambulatory SMA types 2, 3, and 4 were analyzed. Rasch analysis was used to explore item-person targeting, fit statistics, category response functioning, dimensionality, and differential item functioning.

RESULTS

Most items had good fitting with the exception of "toileting" and "respiratory." There were no major floor or ceiling effects, and most items covered a good range of disability with only a negligible breech of uni-dimensionality from eating, dressing, and respiratory items. Differential item function highlighted differences in toileting, turning, transferring, walking, and respiratory items between ambulatory and non-ambulatory populations.

DISCUSSION

Despite subtle misfitting of certain items, mainly related to respiratory and bulbar function, overall modified SMAFRS remained a psychometrically stable and unidimensional outcome measure. There were some differences in measuring properties of certain functional items between ambulatory and non-ambulatory items that need to be taken into consideration in clinical trial design. Overall, the modified SMAFRS is a psychometrically reliable tool in assessment of adult patients with SMA.

Validation of motor and functional scales for the evaluation of adult patients with 5q spinal muscular atrophy

BACKGROUND AND PURPOSE

Mos scales currently used to evaluate spinal muscular atrophy (SMA) patients have only been validated in children. The aim of this study was to assess the construct validity and responsiveness of several outcome measures in adult SMA patients.

METHODS

Patients older than 15 years and followed up in five referral centres for at least 6 months, between October 2015 and August 2020, with a motor function scale score (Hammersmith Functional Motor Scale Expanded [HFMSE], Revised Upper Limb module [RULM]) were included. Bedside functional scales (Egen Klassification [EK2], Revised Amyotrophic Lateral Sclerosis Functional Rating Scale [ALSFRS-R]) were also collected when available. Spearman's rho correlations (rs) and Bangdiwala's concordance test (B) were used to evaluate the scales' construct validity. Monthly slopes of change were used to calculate their responsiveness of the scales.

RESULTS

The study included 79 SMA patients, followed up for a mean of 16 months. All scales showed strong correlations with each other (rs > 0.70). A floor effect in motor function scales was found in the weakest patients (HFMSE < 5 and RULM < 10), and a ceiling effect was found in stronger patients (HFMSE > 60 and RULM > 35). The ALSFRS-R (B = 0.72) showed a strong ability to discriminate between walkers, sitters and non-sitters, and the HFMSE (B = 0.86) between walkers and sitters. The responsiveness was low overall, although in treated patients a moderate responsiveness was found for the ALSFRS-R and HFMSE in walkers (0.69 and 0.61, respectively) and for EK2 in sitters (0.65) and non-sitters (0.60).

CONCLUSIONS

This study shows the validity and limitations of the scales most frequently used to assess adult SMA patients. Overall, bedside functional scales showed some advantages over motor scales, although all showed limited responsiveness.

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.

Management of Spinal Muscular Atrophy in the Adult Population

Spinal muscular atrophy (SMA) is a group of neurodegenerative disorders resulting from the loss of spinal motor neurons. 95% of patients share a pathogenic mechanism of loss of survival motor neuron (SMN) 1 protein expression due to homozygous deletions or other mutations of the SMN1 gene, with the different phenotypes influenced by variable copy numbers of the SMN2 gene. Advances in supportive care, disease modifying treatment and novel gene therapies have led to an increase in the prevalence of SMA, with a third of SMA patients now represented by adults. Despite the growing number of adult patients, consensus on the management of SMA has focused primarily on the pediatric population. As the disease burden is vastly different in adult SMA, an approach to treatment must be tailored to their unique needs. This review will focus on the management of the adult SMA patient as they age and will discuss proper transition of care from a pediatric to adult center, including the need for continued monitoring for osteoporosis, scoliosis, malnutrition, and declining mobility and functioning. As in the pediatric population, multidisciplinary care remains the best approach to the management of adult SMA. Novel and emerging therapies such as nusinersen and risdiplam provide hope for these patients, though these medications are of uncertain efficacy in this population and require additional study.

Neurofilament Levels in CSF and Serum in an Adult SMA Cohort Treated with Nusinersen

OBJECTIVE

To retrospectively evaluate the utility of serum and cerebrospinal fluid (CSF) levels of neurofilament light chain (NfL) and phosphorylated neurofilament heavy chain (pNfH) as biomarkers for spinal muscular atrophy (SMA) progression and response to nusinersen treatment.

METHODS

NfL and pNfH levels were quantified using single molecular array (SIMOA) in CSF of 33 adult SMA patients (SMN copy number 3-5) before and in response to nusinersen treatment. In 11 of the patients, blood serum samples were also collected. CSF NfL and pNfH from patients were compared to CSF Nfs from age-matched controls without neurological disease (n = 6). For patients, pearson correlation coefficients (r) were calculated to investigate associations between Nf levels and other functional outcome measures.

RESULTS

Nf levels were similar between SMA and control adults and showed no change in response to nusinersen treatment in CSF or serum. Cross-sectional analyses showed an increase in CSF NfL and pNfH with age in patients (NfL p = 0.0013; pNfH p = 0.0035) and an increase in CSF NfL in controls (p = 0.002). In non-ambulatory patients, baseline serum pNfH showed a negative correlation with multiple strength and functional assessment metrics including Revised Upper Limb Module (r = -0.822, p = 0.04), upper extremity strength (r = -0.828, p = 0.042), lower extremity strength (r = -0.860, p = 0.028), and total strength (r = -0.870, p = 0.024).

CONCLUSIONS

Nf levels did not change in response to nusinersen in adults with SMA and were not different from controls. In patients and controls, we detected an age-related increase in baseline CSF NfL and pNfH levels. Though some associations were identified, our results suggest Nf levels are not preditive or prognostic biomarkers in this population.

Persistent neuromuscular junction transmission defects in adults with spinal muscular atrophy treated with nusinersen

Objective

Spinal muscular atrophy (SMA) is a motor neuron disease caused by low levels of survival motor neuron (SMN) protein. Prior work in models and patients has demonstrated electrophysiological and morphological defects at the neuromuscular junction (NMJ). Therapeutic development has resulted in clinically available therapies to increase SMN protein levels in patients and improve muscle function. Here we aimed to investigate the effect of SMN restoration (via nusinersen) on NMJ transmission in adults with SMA.

Methods

Participants undergoing nusinersen treatment underwent 3 Hz repetitive nerve stimulation (RNS) of the spinal accessory nerve to assess compound muscle action potential amplitude decrement. Maximum voluntary isometric contraction (MVICT), Revised Upper Limb Module (RULM), and 6 min walk test (6MWT) were assessed for correlations with decrement.

Results

Data from 13 ambulatory (7 men/6 women, mean age 40±11 years) and 11 non-ambulatory (3 men/8 women, mean age 38±12 years) participants were analysed. Cross-sectional analyses of RNS decrement were similar at 14 months of nusinersen (−14.2%±11.5%, n=17) vs baseline (−11.9%±8.3%, n=15) (unpaired t-test, p=0.5202). Longitudinal comparison of decrement in eight participants showed no change at 14 months (−13.9%±6.7%) vs baseline (−16.9%±13.4%) (paired t-test, p=0.5863). Decrement showed strong correlations with measures of MVICT, RULM and 6MWT but not age or disease duration.

Conclusion

Adults with SMA had significant NMJ transmission defects that were not corrected with 14 months of nusinersen treatment. NMJ defects were negatively associated with physical function, and thus may represent a promising target for additive or combinatorial treatments.

Measuring Outcomes in Adults with Spinal Muscular Atrophy - Challenges and Future Directions - Meeting Report

Spinal muscular atrophy (SMA) is a progressive autosomal recessive motor neuron disease which affects 1 in 6,000-10,000 live births, caused by loss of the survival motor neuron 1 gene (SMN1). A major focus of therapeutic developments has been on increasing the full-length SMN protein by increasing the inclusion of exon 7 in SMN2 transcripts, enhancing SMN2 gene expression, stabilizing the SMN protein or replacing the SMN1 gene.In June 2017, FDA and EMA have approved the antisense oligonucleotide Nusinersen as the first treatment for all SMA subtypes without age restriction. While prominent treatment effects have been observed in the earlier stages of the disease and in patients up to 15 years of age, there is only limited data from clinical trials in adult SMA patients. First real-world data from neuromuscular clinical centers suggest a therapeutic benefit of nusinersen with a favourable safety profile also in adult SMA patients: in several cases, relevant improvements of motor function is achieved, which might lead to enhanced autonomy in daily life activities and improved quality of life. Systematic follow-up of the motor status with validated instruments is crucial for an adequate monitoring of the therapeutic effects but most of the widely used scales and scores have been developed and evaluated for the pediatric population only. International neuromuscular experts have met in Frankfurt/Main, Germany in May 2019 to discuss relevant aspects of the diagnostic pathway and patient management in adult SMA. The recommendations and challenges in this patient population are discussed.

Safety, Tolerability, and Effect of Nusinersen Treatment in Ambulatory Adults With 5q-SMA

Objective: To determine the safety and tolerability of nusinersen treatment in ambulatory adults with spinal muscular atrophy (SMA) and investigate the treatment effect on muscle strength, physical function, and motor unit physiology.

Methods: Individuals aged 18 years or older with genetically confirmed 5q SMA, three or more copies of the SMN2 gene, and the ability to ambulate 30 feet were enrolled. Safety outcomes included the number of adverse events and serious adverse events, clinically significant vital sign or laboratory parameter abnormalities. Outcome assessments occurred at baseline (prior to the first dose of nusinersen) and then 2, 6, 10, and 14 months post-treatment.

Results: Six women, seven men (mean age: 37 ± 11, range: 18–59 years) were included for analyses. The most common side effects were headache and back pain, but overall procedures and treatments were well-tolerated. No serious adverse events were reported. Maximal Voluntary Isometric Muscle Contraction Testing (MVICT) and 6-min walk test (6MWT) both showed overall stability with significant increases at 2, 6, and 10 months for the 6MWT. More consistent significant treatment effects were noted on the Hammersmith Functional Motor Scale Expanded, SMA-Functional Rating Scale, and forced vital capacity. Treatment resulted in progressively increased ulnar compound muscle action potential and average single motor unit potential amplitudes, but motor unit number estimation remained stable.

Conclusions: Nusinersen treatment is safe and well-tolerated in ambulatory adults with SMA. Treatment resulted in improved motor function and electrophysiological findings suggest that this improvement may be occurring via improved motor unit reinnervation capacity.

Safety, Tolerability, and Effect of Nusinersen in Non-ambulatory Adults With Spinal Muscular Atrophy

Objective: Investigation of the safety, tolerability, and treatment effect of nusinersen treatment in non-ambulatory adults with spinal muscular atrophy (SMA).

Methods: Non-ambulatory individuals, aged 18 years or older with genetically confirmed 5q SMA were enrolled. In participants with spinal fusion, fluoroscopy guided cervical C1–C2 lateral approach was used. Outcomes at 2, 6, 10, and 14 months post-treatment were compared with baseline assessment. Forced vital capacity (FVC) was the primary outcome, and RULM, HFMSE, the modified SMA-FRS, and ulnar nerve electrophysiology [compound muscle action potential (CMAP), single motor unit size, and motor unit number] were secondary. Adverse and serious adverse events and clinically significant vital sign or lab abnormalities were recorded.

Results: Results from 12 women and 7 men (mean age: 39.7 ± 13.9, range: 21–64 years) were analyzed. No clinically significant changes of vital signs or laboratory parameters were observed. Five participants were hospitalized for pneumonia. Other adverse events included headache, back pain, cervical injection site pain, and upper respiratory and urinary tract infections. High baseline protein/creatinine ratio without significant change on treatment noted in 4 participants. FVC was feasible in all participants. HFMSE and RULM were not feasible in the majority of participants. FVC and functional outcomes were stable without improvement. CMAP and single motor unit potential sizes showed enlargement while motor unit numbers were stable.

Conclusions: Nusinersen, including C1/C2 delivery, was safe overall and well-tolerated. Several outcome measures were limited by floor effect. Overall, treatment resulted in stability of motor outcomes, but motor unit and CMAP size were increased.

Sometimes they come back: New and old spinal muscular atrophy adults in the era of nusinersen

BACKGROUND AND PURPOSE

Following the commercial availability of nusinersen, there have been a number of new referrals of adults with spinal muscular atrophy (SMA) not regularly followed in tertiary-care centers or enrolled in any disease registry.

METHODS

We compared demographics and disease characteristics, including assessment of motor and respiratory function, in regularly followed patients and newcomers subdivided according to the SMA type.

RESULTS

The cohort included 166 adult patients (mean age: 37.09 years): one type I, 65 type II, 99 type III, and one type IV. Of these 166, there were 67 newcomers. There was no significant difference between newcomers and regularly followed patients in relation to age and disease duration. The Hammersmith Functional Motor Scale Expanded and Revised Upper Limb Module scores were higher in the regularly followed patients compared to newcomers in the whole cohort and in both SMA II and II. A difference was also found on ventilatory status (p = 0.013) and Cobb's angle >50° (p = 0.039) between the two subgroups. No difference was found in scoliosis surgery prevalence (p > 0.05).

CONCLUSIONS

Our results showed differences between the two subgroups, even if less marked in the type III patients. In the type II patients, there was a higher proportion of newcomers who were in the severe end of the spectrum. Of the newcomers, only approximately a third initiated treatment, as opposed to the 51% in the regularly followed patients. The identification of patients who were not part of the registries will help to redefine the overall prevalence of SMA and the occurrence of different phenotypes.