High incidence of falls in patients with myotonic dystrophy type 1 and 2: A prospective study

Impact of restricted access to, and low awareness of, mexiletine on people with myotonia: a real-world European survey

Although mexiletine effectively treats myotonia, supply disruptions affected Europe between 2008-2018. MyoPath was a mixed-methods, cross-sectional, market research survey conducted January-June 2018 to evaluate consequences of limited access to/awareness of mexiletine in people with myotonia. Part A: qualitative structured interviews (clinicians; advocates for adult patients); Part B: quantitative online questionnaire completed by people with self-reported history of myotonia. Part A: Interviews (clinicians, n=12; patient advocates, n=5; 12 countries) indicated poor mexiletine awareness among general neurologists. Patients chose between living with myotonia (other treatments were generally unsatisfactory) or importing mexiletine. Part B: Questionnaire respondents, myotonic dystrophy (DM)1, n=213; DM2, n=128; non-dystrophic myotonia (NDM), n=41; other n=8; (11 countries). Of the respondents, 76/390 (20%) people with awareness of/access to mexiletine described profound improvements in myotonia and health-related quality of life following treatment. Respondents with NDM had greatest mexiletine experience (n=28/41). Mexiletine was associated with fewer falls, less muscle stiffness, increased mobility. Treatment interruptions worsened myotonia and were associated with fatigue, pain, dysphagia, breathing difficulty, impaired digestion, poor sleep. However, 36/54 (67%) of currently treated people expressed anxiety about mexiletine's availability: this finding was expected (MyoPath was undertaken before mexiletine's approval in NDM). MyoPath provides the largest European exploration of patients' views regarding impact of mexiletine on myotonia. Anticipated effects of mexiletine differ between people with different myotonic disorders: myotonia is the main symptom in NDM but one of many potential symptoms affecting those with DM. Nevertheless, findings indicate substantial harm caused to people with myotonia when mexiletine awareness/access is limited.

Explanatory factors of dynamic balance impairment in myotonic dystrophy type 1

INTRODUCTION/AIMS

Myotonic dystrophy type 1 (DM1) is a neuromuscular disease affecting many systems and for which muscle weakness is one of the cardinal symptoms. People with DM1 also present with balance-related impairments and high fall risk. The aim of this study was to explore explanatory factors of dynamic balance impairment in the DM1 population.

METHODS

A secondary analysis of data collected as part of a larger study was performed. The Mini Balance Evaluation System Test (Mini-BESTest) was used to assess dynamic balance. Age, sex, and CTG repeat length in blood were retrieved from medical records and research files. The maximal isometric muscle strength of five lower limb muscle groups (hip flexors and extensors, knee flexors and extensors, and ankle dorsiflexors) was quantitatively assessed as well as fatigue. Standard multiple regression analysis was used.

RESULTS

Fifty-two individuals (31 men) aged between 24 and 81 years were included. The final model explains 65.9% of the balance score; ankle dorsiflexor muscle strength was the strongest explanatory factor, followed by CTG repeat length, age and fatigue to a lesser extent.

DISCUSSION

Dynamic balance is impaired in people with DM1. Results of this study suggest that rehabilitation interventions aimed at improving strength of the ankle dorsiflexors and managing fatigue could help to improve dynamic balance in this specific population.

Assessment of muscular strength and functional capacity in the juvenile and adult myotonic dystrophy type 1 population: a 3-year follow-up study

INTRODUCTION

Myotonic dystrophy type 1 (DM1) is a progressive, multisystemic, and autosomal dominant disease. Muscle wasting and weakness have been associated with impaired functional capacity and restricted social participation in affected individuals. The disease's presentation is very heterogenous and its progression is still under-documented.

OBJECTIVE

The aim of the study was to document the progression of muscular strength and functional capacity in the DM1 population over a 3-year period.

METHODS

Twenty-three individuals with juvenile or adult phenotypes of DM1 were recruited to complete clinical assessments in 2016 and 2019. Maximal isometric muscle strength (MIMS) was evaluated with quantified muscle testing and functional capacity was evaluated with the Mini-BESTest, the 10-m walk test at comfortable and maximal speeds, the Timed Up and Go and the 6-min walk test. Participants also completed three questionnaires: DM1-Activ, Upper Extremity Functional Index and Lower Extremity Functional Scale (LEFS). Subgroup analyses were evaluated for sex, phenotype, and type of physical activity practiced during the 3-year period.

RESULTS

For the whole group, there was a significant decline in the scores of the Mini-BESTest and the LEFS. Also, MIMS significantly declined for prehension, lateral pinch as well as for hip abductors, knee extensors and ankle dorsiflexors muscle groups. Subgroups analyses revealed that men lost more MIMS than women, and that adult phenotype lost more MIMS than juvenile phenotype.

CONCLUSION

Quantified muscle testing is a better indicator of disease progression over a 3-year period than functional tests. Phenotype and sex are important factors that influence the progression of DM1.

How to capture activities of daily living in myotonic dystrophy type 2?

Myotonic dystrophy type 2 (DM2) lacks validated patients´ reported outcomes (PROs). This represents a limit for monitoring disease progression and perceived efficacy of symptomatic treatments. Our aim was to investigate whether PROs for activities of daily living designed for other neuromuscular diseases could be used in DM2. Sixty-six DM2 patients completed the following PROs: DM1-Activ-c, Rasch-built Pompe-specific activity (R-PAct) scale, McGill-pain questionnaire, fatigue and daytime sleepiness scale and Beck depression inventory (BDI-II). Clinical data and motor outcome measures (6-minutes walking test - 6MWT, manual muscle testing, quick motor function test and myotonia behavior scale) were collected as well. Patients underwent one visit at baseline and one after 10 months. Ceiling/flooring effects, criterion validity and discriminant validity were calculated. DM1-activ-c and R-PAct showed acceptable ceiling effects despite being built for myotonic dystrophy type 1 and Pompe disease, respectively. The difficulty hierarchy of the single items was better preserved in R-PAct than in DM1-Activ-c. Both tests showed excellent criterion validity highly correlating with 6MWT, quick motor function test, myalgia and disease duration. They could partially discriminate patients with different disability grades. These results suggest that DM1-Activ-c, slightly better than R-PAct, might be adopted for monitoring activities of daily living also in DM2, at least until disease-specific PROs will be available.

Validity of the Mini-BESTest in adults with myotonic dystrophy type 1

INTRODUCTION

Myotonic dystrophy type 1 (DM1) is a multisystemic neuromuscular disease that causes balance problems. The objective of this study was to assess the construct validity of the Mini-BESTest among adults with DM1.

METHODS

Fifty-nine individuals with late-onset or adult phenotypes of DM1 were recruited. Participants performed the Mini-BESTest, 10-Meter Walk Test (10mWT), 6-Minute Walk Test (6MWT), and Timed Up & Go (TUG) and were questioned on their tendency to lose balance and whether they fell in the past month.

RESULTS

Scores on the Mini-BESTest were significantly different between phenotypes and CTG repeat numbers (P < .02). Significant correlations were found with the 10mWT, 6MWT, and the TUG (r = 0.77-0.84; P < .001). A cutoff score of 21.5 was found to identify fallers with 90% posttest accuracy.

DISCUSSION

The Mini-BESTest demonstrates evidence of construct validity when assessing balance in the DM1 population.

Validation of Motor Outcome Measures in Myotonic Dystrophy Type 2

Introduction: Myotonic dystrophy type 2 (DM2) lacks disease-specific, validated, motor outcome measures (OMs), and patients' reported outcomes (PROs). This represents a limit for the monitoring of disease progression and treatment response. Our aim was to identify the most appropriate OMs to be translated in clinical practice and clinical trials on DM2. This study has been registered on clinicaltrials.gov NCT03603171 (https://clinicaltrials.gov/ct2/show/NCT03603171). Methods: Sixty-six patients with genetically confirmed DM2 underwent a baseline and a follow-up visit after 1 year. The tested OMs included: hand opening time, pressure pain threshold (PPT), manual muscle testing (MMT), hand held dynamometry (HHD), scale for the assessment and rating of ataxia (SARA), quantitative motor function test (QMFT), gait stairs Gowers chair (GSGC), 30-s sit to stand test, functional index 2 (FI-2) and 6MWT. The PROs included DM1-Active-C, Rasch-built Pompe-specific activity scale (R-Pact), fatigue and daytime sleepiness (FDSS), brief pain inventory short form (BPI-sf), myotonia behavior scale (MBS), and the McGill pain questionnaire. Results: All patients completed the MBS and the results correlated well with the hand-opening time. The PPT showed a low reliability, no correlation with pain questionnaires, and did not differentiate patients with or without myalgia. Both muscle strength assessments, MMT and HHD, showed good construct validity. The QMFT showed an acceptable ceiling effect (14.5%), good convergent and differential validity and performed overall better than GSGC. The SARA score showed high flooring effect and is not useful in DM2. 6MWT proved a valid outcome measure in DM2. The 30-s sit to stand is a feasible test with good convergent validity, showing a flooring effect of 20% as it cannot be used in more severely affected patients. The FI-2 is time-consuming and has a high ceiling effect. At the 1-year visit the only assessments able to detect a worsening of DM2 were HHD, QMFT, and 6MWT, which are the most sensitive to change, and therefore clinically meaningful OMs in DM2. Conclusion: The clinical meaningful motor outcome measures that best depict the multifaceted phenotype of DM2 and its slow progression are MBS, MMT, or HHD (depending on the clinical setting), QMFT, and the 6MWT.