title: The use of muscle strength assessed with handheld dynamometers as a non-invasive biological marker in myotonic dystrophy type 1 patients: a multicenter study.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Canadian Forces Health Services Headquarter, Directorate Medical Policy, National Defense of Canada, 1745 Alta Vista Dr, Ontario (K1A 0K6), Ottawa, Canada. ljhebert@videotron.ca
authors.forename: Luc J
authors.initials: LJ
authors.lastname: Hébert
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Remec
authors.forename: Joanne
authors.initials: J
authors.lastname: Saulnier
authors.forename: Christophe
authors.initials: C
authors.lastname: Vial
authors.forename: Jack
authors.initials: J
authors.lastname: Puymirat
mesh_terms: D000328:Adult; D000843:Ankle Joint / Q000502:physiology; D015415:Biomarkers; D003937:Diagnosis, Differential; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology; D053580:Muscle Strength / Q000502:physiology; D053581:Muscle Strength Dynamometer / Q000592:standards*; D018908:Muscle Weakness / Q000175:diagnosis* / Q000503:physiopathology; D018482:Muscle, Skeletal / Q000503:physiopathology*; D009223:Myotonic Dystrophy / Q000175:diagnosis* / Q000503:physiopathology; D011237:Predictive Value of Tests; D016059:Range of Motion, Articular / Q000502:physiology
chemical_list: D015415:Biomarkers
references.citation: Scand J Rehabil Med. 1995 Jun;27(2):109-17
references.pmid: 7569820
references.citation: Am J Sports Med. 1996 Nov-Dec;24(6):800-9
references.pmid: 8947403
references.citation: Dev Med Child Neurol. 2005 Jul;47(7):478-85
references.pmid: 15991869
references.citation: Clin Rehabil. 2008 Oct-Nov;22(10-11):902-10
references.pmid: 18955422
references.citation: Arch Phys Med Rehabil. 2007 Oct;88(10):1289-97
references.pmid: 17908571
references.citation: Muscle Nerve. 2007 Jan;35(1):36-42
references.pmid: 16969838
references.citation: J Neurol Neurosurg Psychiatry. 2006 Nov;77(11):1282-3
references.pmid: 17043296
references.citation: Arch Phys Med Rehabil. 1987 Jul;68(7):454-8
references.pmid: 3606371
references.citation: Am J Phys Med Rehabil. 1995 Sep-Oct;74(5 Suppl):S104-16
references.pmid: 7576418
references.citation: Neuromuscul Disord. 2001 Jul;11(5):441-6
references.pmid: 11404114
references.citation: Arch Phys Med Rehabil. 2004 Jan;85(1):77-80
references.pmid: 14970972
references.citation: Clin Rehabil. 1999 Feb;13(1):64-73
references.pmid: 10327099
references.citation: Arch Phys Med Rehabil. 1995 Jul;76(7):612-20
references.pmid: 7605179
references.citation: Neurology. 2001 Feb 13;56(3):336-40
references.pmid: 11171898
references.citation: Can J Neurol Sci. 2003 May;30(2):129-36
references.pmid: 12774952
references.citation: Percept Mot Skills. 1999 Jun;88(3 Pt 1):899-902
references.pmid: 10407897