P.33Quantified muscle testing: the right way to assess muscle strength impairments in DM1

Abstract

Myotonic dystrophy type 1 (DM1) is a degenerative neuromuscular disease in which maximal muscle strength (MMS) loss is a strong indicator of physical limitations. As standardized protocols with high quality hand held dynamometers (HHD) are now available, it is possible to use precise, valid, reliable, and responsive MMS evaluation in DM1. In previous studies, we assessed, in various healthy populations, the intra and inter-rater reliability, standard error of measurement (SEM), minimal detectable change (MDC), and the concurrent validity (CVal) with the BIODEX as gold standard, of QMT using a HHD for 12 muscle groups of both lower (hip abductors, flexors and extensors; knee flexors and extensors (KE); ankle evertors, dorsiflexors and plantarflexors) and upper limbs (shoulder abductors and lateral rotators; elbow flexors and extensors). In healthy participants, using intraclass correlation coefficient (ICC), we have shown that the intra- and inter-rater reliability was varying from 0.84 to 0.98 and 0.75 to 0.97, respectively. The SEM was varying across muscle groups from 0.5 Nm (ankle dorsiflexors) to 6.1 Nm (hip flexors) while the MDC was also relatively low but only assessed for the ankle plantarflexors (12.7 Nm). In 19 men with the adult form of DM1 and specifically for the KE, the intra-rater reliability was excellent with an ICC of 0.98 (0.96-0.99: 95% confidence interval) while the SEM and MDC values were 1.05 Nm and 2.92 Nm, respectively. Concurrent validity of QMT of KE muscle group with the Biodex was also excellent with a Spearman's correlation of ρ = 0.98. The good to excellent metrological qualities of QMT using HHD protocols make of QMT a method of choice, in a clinical or research setting, to precisely evaluate muscle strength impairments in DM1. QMT should be considered the most appropriate method for monitoring muscular changes for such a slow progressive disease. So, let's talk about what is required for you to adopt such a protocol, and why not?