Affiliations: [a] Department of Rehabilitation, Faculty of Medicine, Laval University, QC, Canada | [b] Department of Radiology-Nuclear Medicine, Faculty of Medicine, Laval University, QC, Canada | [c] Centre for Interdisciplinary Research in Rehabilitation and Social Integration (CIRRIS), QC, Canada | [d] Neuro-rehabilitation Service, Hôpital Pierre Werteimer (Groupement HospitalierEst), Lyon, France | [e] Department of Electro-neurophysiology and Muscular Pathology, HôpitalPierre Werteimer (Groupement Hospitalier Est), Lyon, France | [f] Neuromuscular Physiology and Evaluation Laboratory, Neuromuscular Investigation Center, Institute of Myology, Paris, France | [g] Unit of Human Genetics, Hôpital de l’Enfant-Jésus, CHU Research Center, QC, Canada
Abstract: Background:In Myotonic Dystrophy type 1 (DM1) patients, ankle muscles are affected early and this impairment is reported to be a good biological marker for longitudinal studies. Objective:To characterize the ankle dorsiflexion (DF) and eversion (EV) maximal isometric muscle strength changes in adult DM1 patients over 5 years using a standardized handheld dynamometer protocol and the Myoankle method, compare the changes measured with both methods and to the standard error of measurement, and verify the relationship between ankle muscle strength and gait performance. Methods:The maximal isometric muscle strength of ankle DF and EV in DM1 patients from Quebec and Lyon was assessed at baseline, 18, 36 and 60 months using a handheld dynamometer (HHD) protocol and the MyoAnkle method. Results:There was a decrease of torque in DF/EV of 36.0% /31.3% and 27.7% /35.5% for the Quebec and Lyon cohorts respectively (p≤0.01), but not in a linear way. In most cases (82.5% ), the changes observed were greater than the standard error of measurement. DF torque measures taken by the two methods (HHD and MyoAnkle) were highly correlated (rp = 0.97– 0.98, p < 0.001). Conclusion:Muscle strength ankle impairments are clinically meaningful in DM1 and can be accurately monitored using quantitative testing to measure the efficacy of therapeutic trials.