Lower limb muscle strength impairment in late‐onset and adult myotonic dystrophy type 1 phenotypes

• Published in: Muscle & nerve 2017-07, Vol.56 (1), p.57-63
• Main Authors: Petitclerc, Émilie, Hébert, Luc J., Mathieu, Jean, Desrosiers, Johanne, Gagnon, Cynthia
• Format: Article
• Language: English
• Subjects: Adult; Aged; Clinical trials; Dystrophy; Electromyography; Female; Genotype & phenotype; Humans; Impairment; Isometric Contraction - physiology; Lower Extremity - innervation; lower limb; Male; Medical research; Middle Aged; Muscle strength; Muscle Strength - physiology; Muscle Weakness - etiology; Muscle, Skeletal - physiopathology; Myotonic dystrophy; Myotonic Dystrophy - complications; myotonic dystrophy type 1 (DM1); outcome measures; phenotype comparison; Physical activity; quantitative muscle testing; Severity of Illness Index; strength; Yield strength; Young Adult
• ISSN: 0148-639X; 1097-4598
• DOI: 10.1002/mus.25451

ABSTRACT Introduction Lower limb strength has never been characterized separately for late‐onset and adult myotonic dystrophy type 1 (DM1) phenotypes. Methods The purpose of this study was to: (1) describe and compare lower limb strength between the 2 DM1 phenotypes; and (2) compare the impairment profiles obtained from 2 assessment methods [manual (MMT) and quantitative (QMT) muscle testing] among 107 patients. Results Both MMT and QMT showed more pronounced weakness in the adult phenotype. In the late‐onset phenotype, although MMT showed normal strength, QMT revealed a loss of 11.7%–20.4%. Participants with grade 1 or 2 on the Muscle Impairment Rating Scale had weakness detected using QMT, which suggests earlier muscle impairment than MMT alone would suggest. Conclusions To avoid muscle wasting, physical activity recommendations should be made for the late‐onset phenotype and in the early stages of the disease for the adult phenotype. MMT is not recommended for use in clinical trials. Muscle Nerve 56: 57–63, 2017.