The use of muscle strength assessed with handheld dynamometers as a non-invasive biological marker in myotonic dystrophy type 1 patients: a multicenter study
1 Canadian Forces Health Services Headquarter, Directorate Medical Policy, National Defense of Canada, 1745 Alta Vista Dr, Ontario (K1A 0K6), Ottawa, Canada
2 Department of Radiology, Faculty of Medicine, Laval University, Pavillon Vandry (room 3370), Quebec (G1K 7P4), Quebec, Canada
3 Service de neuro-rééducation, 59 boulevard Pinel, 69677 Bron cedex, Lyon, France
4 Institut de réadaptation en déficience physique de Québec, 525, boulevard Wilfrid-Hamel, Quebec, (G1M 2S8), Quebec, Canada
5 Department of Electro-neurophysiology and muscular pathology, Hôpital Pierre Werteimer Groupement Hospitalier Est, 59 boulevard Pinel, 69677 Bron cedex, Lyon, France
6 Human Genetic Research Unit, Centre Hospitalier de l'Université Laval, 2705 boulevard Laurier, Quebec (G1V 4G2), Quebec, Canada
BMC Musculoskeletal Disorders 2010, 11:72 doi:10.1186/1471-2474-11-72Published: 18 April 2010
Myotonic 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.
The 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.
With 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.
The 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.