A 9-year follow-up study of quantitative muscle strength changes in myotonic dystrophy type 1

Abstract

Myotonic dystrophy type 1 (DM1) is a neuromuscular disorder presenting with major muscle impairments. However, few studies have addressed muscle strength progression using quantitative methods. The aims of this study were to document muscle strength changes in eight muscle groups among adults with DM1 over a 9-year period, and to compare this progression between phenotypes (adult and late-onset) and sex. Patients with a genetic diagnosis of DM1 with the late-onset or the adult phenotype were recruited at baseline through the clinical registry of the Saguenay Neuromuscular Clinic. The maximum isometric muscle strength was measured at baseline and 9 years later using a standardized protocol of quantitative muscle testing. Muscle groups included were shoulder abductors, elbow flexors/extensors, wrist extensors, hip flexors, knee flexors/extensors, and ankle dorsiflexors. For the whole group, a mean loss of 24.5-52.8% was observed over the 9-year period for all muscle groups, except for hip flexors which remained stable. Generally, men were stronger and showed a significant greater rate of decline of muscle strength than women. The adult and late-onset phenotypes taken separately also showed a significant and similar decline over the 9-year period, except for the wrist and knee extensors where muscle strength of participants with the adult phenotype decreased faster than in the late-onset phenotype. The similar rate of decline of muscle strength loss observed between phenotypes highlights the need to develop interventions to prevent this decline, even for patients with the late-onset phenotype who are often considered as mildly impaired, and therefore neglected by the rehabilitation services.

Analysis of the functional capacity outcome measures for myotonic dystrophy

“…Differences between adult‐onset and late‐onset phenotypes have been reported before . In addition, functional performance can differ due to age, gender, and body composition as reported not only in DM1 but also in healthy populations and other neurological disorder .…”

“…For example, after performing this model, walking tests (i.e., 6MWT and 10mWT) significance between male and female disappeared and the difference in 30SSS became significant highlighting the relevant influence of BMI and MIRS in these scores. The late‐onset phenotype subgroup differed significantly from the adult phenotype in all outcomes, which proves once more that generalizability of results should be cautious when considering data from mixed‐phenotypic samples and the association with muscular strength as measured by MIRS . However, using five categories of disease severity (i.e., MIRS) as compared to only two (i.e., Phenotype) was shown to be more strongly associated with patient performance.…”

“…The inclusion criteria were: a genetically confirmed diagnosis of DM1; ≥18 years; ability to provide informed consent and walk independently (assistive devices and orthotics allowed) for at least 10 m. The cohort recruited at one of the study sites (Newcastle) was followed up for 1 year as part of the longitudinal analysis. Patients were classified as late onset if they met two of the three following criteria: (1) first symptoms reported at the age of ≥40 years; (2) ≤200 CTG repeats; and (3) a MIRS score of I or II; otherwise they were categorized as adult (classic) phenotype . Participants with an early adult (juvenile) phenotype (i.e., first symptoms reported before 20 years old) were included in the adult phenotype group.…”

“…This study focused on the exploration of the OMMYD FCOM tests: (1) 6MWT; (2) 10mWT; referring walking at comfortable speed (i.e., patient’s selected pace); (3) 10mW/RT, referring to walking at the maximum possible and safe speed, allowing running if possible; (4) 30SSS; and (5) 9HPT . The following outcomes were considered for cross comparisons at baseline: (1) demographic characteristics (i.e., age, sex, age since disease onset, CTG mode at baseline, height, and weight); (2) muscle strength and capacity including: quantitative muscle testing (QMT) of ankle dorsiflexion, knee extension, and hip flexion following standardized procedures and using Microfet2 and including the best out of three attempts for analysis; (3) the MIRS which is a five‐categories classification method for assessing disease progression as measured by muscle weakness manifestations and manual muscle testing; (4) SARA scale which assess movement co‐ordination and has been reported as possible assessment of disease severity in DM1 regardless of the presence of ataxia or not; and (5) disease‐specific patient‐reported outcome measures (PROM) that assess perceived functional performance which included the DM1‐Activ C Rasch built scale and the Myotonic Dystrophy Health Index (MDHI) subscales of ability to perform activities and mobility …”

Intra-Rater Reliability and Concurrent Validity of Quantified Muscle Testing for Maximal Knee Extensors Strength in Men with Myotonic Dystrophy Type 1

“…Skeletal muscles are notably affected and patients with the disease experience slowly progressive muscle atrophy and weakness [4,7]. In the adult form, it has been demonstrated that affected people lose 24.5 to 52.8% of their maximal strength on a 9-year period depending on the muscle group evaluated [8]. Furthermore, it has been reported that the disease affects skeletal muscles differently in men and women [8][9][10].…”