Abstract
BackgroundMyotonic dystrophy type 1 (DM1) is a multisystem disorder that demonstrates variable symptoms and rates of progression. Muscle weakness is considered one of the main problems with a clinical picture that is characterized by distal weakness of the limbs progressing to proximal weakness. The main objective of this study was to characterize the maximal strength of ankle eversion and dorsiflexion in DM1 patients. Manual and handheld dynamometer (HHD) muscle testing were also compared.MethodsThe maximal strength of 22 patients from Quebec (mean age = 41,1 ± 13,8) and 24 from Lyon (mean age = 41,6 ± 10,2) were compared to 16 matched controls.ResultsWith the use of HHD, an excellent reproducibility of the torque measurements was obtained for both centers in eversion (R2 = 0,94/Quebec; 0,89/Lyon) and dorsiflexion (R2 = 0,96/Quebec; 0,90/Lyon). The differences between 3 groups of DM1 (mild, moderate, severe) and between them and controls were all statistically significant (p < 0,001). No statistical differences between sites were observed (p > 0.05). The degree of muscle strength decline in dorsiflexion (eversion) were 60% (47%), 77% (71%), and 87% (83%) for DM1 with mild, moderate, and severe impairments, respectively. The smallest mean difference between all DM1 patients taking together was 2.3 Nm, a difference about twice than the standard error of measurement. There was a strong relationship between eversion and dorsiflexion strength profiles (R2 = 0,87;Quebec/0,80;Lyon). Using a 10-point scale, manual muscle testing could not discriminate between the 3 groups of DM1 patients.ConclusionsThe HHD protocol showed discriminative properties suitable for multicentre therapeutic trial. The present results confirmed the capacity of quantitative muscle testing to discriminate between healthy and DM1 patients with different levels of impairments. This study is a preliminary step for the implementation of a valid, reliable and responsive clinical outcome for the measurement of muscle impairments with this population.
Highlights
Myotonic dystrophy type 1 (DM1) is a multisystem disorder that demonstrates variable symptoms and rates of progression
Participants Inclusion criteria were limited to DM1 patients older than 18 years old, weakness of the tibialis anterior (TA) as assessed by manual muscle testing, DM1 diagnosis confirmed by molecular testing, and to the patient' ability to take part in manual and quantified muscle strength assessment
The method used to assess muscle strength must be simple, easy to perform for the clinician and it must be sensitive enough to allow the early detection of distal muscle weaknesses
Summary
Myotonic dystrophy type 1 (DM1) is a multisystem disorder that demonstrates variable symptoms and rates of progression. Previous studies with myotrophic dystrophy have characterized muscle strength deficits, established baseline data and compared the rate of change in strength of proximal and distal muscles. Different tools were used to assess the muscular impairments including manual muscle testing, timed functional tests, quantitative motor evaluation, isokinetic systems, Jamar dynamometer, and hand held dynamometers [2,3,4,5,6,7]. From those studies, few consensuses have emerged. Even when using reliable scales, lacks sensitivity to detect subtle changes in muscular impairment and is not appropriate to measure the efficacy in short-term therapeutic trials, and neither suitable for longitudinal studies for which a discriminatory measure is required [8]
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