Rasch analysis of clinical outcome measures in spinal muscular atrophy

Spinal muscular atrophy functional composite score: A functional measure in spinal muscular atrophy

INTRODUCTION

With clinical trials underway, our objective was to construct a composite score of global function that could discriminate among people with spinal muscular atrophy (SMA).

METHODS

Data were collected from 126 participants with SMA types 2 and 3. Scores from the Hammersmith Functional Motor Scale-Expanded and Upper Limb Module were expressed as a percentage of the maximum score and 6-minute walk test as percent of predicted normal distance. A principal component analysis was performed on the correlation matrix for the 3 percentage scores.

RESULTS

The first principal component yielded a composite score with approximately equal weighting of the 3 components and accounted for 82% of the total variability. The SMA functional composite score, an unweighted average of the 3 individual percentage scores, correlated almost perfectly with the first principal component.

CONCLUSIONS

This combination of measures broadens the spectrum of ability that can be quantified in type 2 and 3 SMA patients.

Upper limb evaluation and one-year follow up of non-ambulant patients with spinal muscular atrophy: an observational multicenter trial

Assessment of the upper limb strength in non-ambulant neuromuscular patients remains challenging. Although potential outcome measures have been reported, longitudinal data demonstrating sensitivity to clinical evolution in spinal muscular atrophy patients are critically lacking. Our study recruited 23 non-ambulant patients, 16 patients (males/females = 6/10; median age 15.4 years with a range from 10.7 to 31.1 years) with spinal muscular atrophy type II and 7 patients (males/females = 2/5; median age 19.9 years with a range from 8.3 to 29.9 years) with type III. The Brooke functional score was on median 3 with a range from 2 to 6. The average total vital capacity was 46%, and seven patients required non-invasive ventilation at night. Patients were assessed at baseline, 6 months, and 1 year using the Motor Function Measure and innovative devices MyoGrip, MyoPinch, and MoviPlate, which assess handgrip strength, key pinch strength, and hand/finger extension-flexion function, respectively. The study demonstrated the feasibility and reliability of these measures for all patients, and sensitivity to negative changes after the age of 14 years. The younger patients showed an increase of the distal force in the follow-up period. The distal force measurements and function were correlated to different functional scales. These data represent an important step in the process of validating these devices as potential outcome measures for future clinical trials.

The Genetics of Spinal Muscular Atrophy: Progress and Challenges

Spinal muscular atrophies (SMAs) are a group of inherited disorders characterized by motor neuron loss in the spinal cord and lower brainstem, muscle weakness, and atrophy. The clinical and genetic phenotypes incorporate a wide spectrum that is differentiated based on age of onset, pattern of muscle involvement, and inheritance pattern. Over the past several years, rapid advances in genetic technology have accelerated the identification of causative genes and provided important advances in understanding the molecular and biological basis of SMA and insights into the selective vulnerability of the motor neuron. Common pathophysiological themes include defects in RNA metabolism and splicing, axonal transport, and motor neuron development and connectivity. Together these have revealed potential novel treatment strategies, and extensive efforts are being undertaken towards expedited therapeutics. While a number of promising therapies for SMA are emerging, defining therapeutic windows and developing sensitive and relevant biomarkers are critical to facilitate potential success in clinical trials. This review incorporates an overview of the clinical manifestations and genetics of SMA, and describes recent advances in the understanding of mechanisms of disease pathogenesis and development of novel treatment strategies.

Upper limb module in non-ambulant patients with spinal muscular atrophy: 12 month changes

Recent studies have suggested that in non-ambulant patients affected by spinal muscular atrophy the Upper Limb Module can increase the range of activities assessed by the Hammersmith Functional Motor Scale Expanded. The aim of this study was to establish 12-month changes in the Upper Limb Module in a cohort of non-ambulant spinal muscular atrophy patients and their correlation with changes on the Hammersmith Functional Motor Scale Expanded. The Upper Limb Module scores ranged between 0 and 17 (mean 10.23, SD 4.81) at baseline and between 1 and 17 at 12 months (mean 10.27, SD 4.74). The Hammersmith Functional Motor Scale Expanded scores ranged between 0 and 34 (mean 12.43, SD 9.13) at baseline and between 0 and 34 at 12 months (mean 12.08, SD 9.21). The correlation betweeen the two scales was 0.65 at baseline and 0.72 on the 12 month changes. Our results confirm that the Upper Limb Module can capture functional changes in non-ambulant spinal muscular atrophy patients not otherwise captured by the other scale and that the combination of the two measures allows to capture changes in different subgroups of patients in whom baseline scores and functional changes may be influenced by several variables such as age.

Emotional vitality in caregivers: application of Rasch Measurement Theory with secondary data to development and test a new measure

OBJECTIVE

To describe the practical steps in identifying items and evaluating scoring strategies for a new measure of emotional vitality in informal caregivers of individuals who have experienced a significant health event.

DESIGN

The psychometric properties of responses to selected items from validated health-related quality of life and other psychosocial questionnaires administered four times over a one-year period were evaluated using Rasch Measurement Theory.

SETTING

Community.

SUBJECTS

A total of 409 individuals providing informal care at home to older adults who had experienced a recent stroke.

MAIN MEASURES

Rasch Measurement Theory was used to test the ordering of response option thresholds, fit, spread of the item locations, residual correlations, person separation index, and stability across time.

RESULTS

Based on a theoretical framework developed in earlier work, we identified 22 candidate items from a pool of relevant psychosocial measures available. Of these, additional evaluation resulted in 19 items that could be used to assess the five core domains. The overall model fit was reasonable (χ(2) = 202.26, DF = 117, p = 0.06), stable across time, with borderline evidence of multidimensionality (10%). Items and people covered a continuum ranging from -3.7 to +2.7 logits, reflecting coverage of the measurement continuum, with a person separation index of 0.85. Mean fit of caregivers was lower than expected (-1.31 ±1.10 logits).

CONCLUSION

Established methods from the Rasch Measurement Theory were applied to develop a prototype measure of emotional vitality that is acceptable, reliable, and can be used to obtain an interval level score for use in future research and clinical settings.

Rasch analysis of the motor function measure in patients with congenital muscle dystrophy and congenital myopathy

OBJECTIVES

To monitor treatment effects in patients with congenital myopathies and congenital muscular dystrophies, valid outcome measures are necessary. The Motor Function Measure (MFM) was examined for robustness, and changes are proposed for better adequacy.

DESIGN

Observational study based on data previously collected from several cohorts.

SETTING

Nineteen departments of physical medicine or neuromuscular consultation in France, Belgium, and the United States.

PARTICIPANTS

Patients (N=289) aged 5 to 77 years.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

A Rasch analysis examined the robustness of the MFM across the disease spectrum. The 3 domains of the scale (standing position and transfers, axial and proximal motor function, and distal motor function) were independently examined with a partial credit model.

RESULTS

The original 32-item MFM did not sufficiently fit the Rasch model expectations in either of its domains. Switching from a 4- to a 3-category response scale in 18 items restored response order in 16. Various additional checks suggested the removal of 7 items. The resulting Rasch-scaled Motor Function Measure with 25 items for congenital disorders of the muscle (Rs-MFM25(CDM)) demonstrated a good fit to the Rasch model. Domain 1 was well targeted to the whole severity spectrum-close mean locations for items and persons (0 vs 0.316)-whereas domains 2 and 3 were better targeted to severe cases. The reliability coefficients of the Rs-MFM25(CDM) suggested sufficient ability for each summed score to distinguish between patient groups (0.9, 0.8, and 0.7 for domains 1, 2, and 3, respectively). A sufficient agreement was found between results of the Rasch analysis and physical therapists' opinions.

CONCLUSIONS

The Rs-MFM25(CDM) can be considered a clinically relevant linear scale in each of its 3 domains and may be soon reliably used for assessment in congenital disorders of the muscle.

Molecular therapeutic strategies for spinal muscular atrophies: current and future clinical trials

BACKGROUND

Spinal muscular atrophy (SMA) is an autosomal recessive motor neuron disease caused by mutations in the survival motor neuron gene (SMN1) and the leading genetic cause of infant mortality. Currently, there is no effective treatment other than supportive care.

OBJECTIVE

This article provides a general overview of the main aspects that need to be taken into account to design a more efficient clinical trial and to summarize the most promising molecular trials that are currently in development or are being planned for the treatment of SMA.

METHODS

A systematic review of the literature was performed, identifying key clinical trials involving novel molecular therapies in SMA. In addition, abstracts presented at the meetings of the Families of Spinal Muscular Atrophy were searched and the Families of Spinal Muscular Atrophy Web site was carefully analyzed. Finally, a selection of SMA clinical trials registered at clinical-trials.gov has been included in the article.

RESULTS

The past decade has seen a marked advancement in the understanding of both SMA genetics and molecular mechanisms. New molecules targeting SMN have shown promise in preclinical studies, and various clinical trials have started to test the drugs that were discovered through basic research.

CONCLUSIONS

Both preclinical and early clinical trial results involving novel molecular therapies suggest that the clinical care paradigm in SMA will soon change.

Spinal muscular atrophy: development and implementation of potential treatments

In neurodegenerative disorders, effective treatments are urgently needed, along with methods to determine whether treatment worked. In this review, we discuss the rapid progress in the understanding of recessive proximal spinal muscular atrophy and how this is leading to exciting potential treatments of the disease. Spinal muscular atrophy is caused by loss of the survival motor neuron 1 (SMN1) gene and reduced levels of SMN protein. The critical downstream targets of SMN deficiency that result in motor neuron loss are not known. However, increasing SMN levels has a marked impact in mouse models, and these therapeutics are rapidly moving toward clinical trials. Promising preclinical therapies, the varying degree of impact on the mouse models, and potential measures of treatment effect are reviewed. One key issue discussed is the variable outcome of increasing SMN at different stages of disease progression.