title: Validation and clinical significance of the Childhood Myositis Assessment Scale for assessment of muscle function in the juvenile idiopathic inflammatory myopathies.
abstract: OBJECTIVE
  To examine the measurement characteristics of the Childhood Myositis Assessment Scale (CMAS) in children with juvenile idiopathic inflammatory myopathy (juvenile IIM), and to obtain preliminary data on the clinical significance of CMAS scores.
  
  
  METHODS
  One hundred eight children with juvenile IIM were evaluated on 2 occasions, 7-9 months apart, using various measures of physical function, strength, and disease activity. Interrater reliability, construct validity, and responsiveness of the CMAS were examined. The minimum clinically important difference (MID) and CMAS scores corresponding to various degrees of physical disability were estimated.
  
  
  RESULTS
  The intraclass correlation coefficient for 26 patients assessed by 2 examiners was 0.89, indicating very good interrater reliability. The CMAS score correlated highly with the Childhood Health Assessment Questionnaire (C-HAQ) score and with findings on manual muscle testing (MMT) (r(s) = -0.73 and 0.73, respectively) and moderately with physician-assessed global disease activity and skin activity, parent-assessed global disease severity, and muscle magnetic resonance imaging (r(s) = -0.44 to -0.61), thereby demonstrating good construct validity. The standardized response mean was 0.81 (95% confidence interval 0.53, 1.09) in patients with at least 0.8 cm improvement on a 10-cm visual analog scale for physician-assessed global disease activity, indicating strong responsiveness. In bivariate regression models predicting physician-assessed global disease activity, MMT remained significant in models containing the CMAS (P = 0.03) while the C-HAQ did not (P = 0.4). Estimates of the MID ranged from 1.5 to 3.0 points on a 0-52-point scale. CMAS scores corresponding to no, mild, mild-to-moderate, and moderate physical disability, respectively, were 48, 45, 39, and 30.
  
  
  CONCLUSIONS
  The CMAS exhibits good reliability, construct validity, and responsiveness, and is therefore a valid instrument for the assessment of physical function, muscle strength, and endurance in children with juvenile IIM. Preliminary data on MID and corresponding levels of disability should aid in the clinical interpretation of CMAS scores when assessing patients with juvenile IIM.
authors.affiliation: IWK Health Centre and Dalhousie University, 5850 University Avenue, Halifax, Nova Scotia B3J 3G9, Canada. adam.huber@iwk.nshealth.ca
authors.forename: Adam M
authors.initials: AM
authors.lastname: Huber
authors.forename: Brian M
authors.initials: BM
authors.lastname: Feldman
authors.forename: Robert M
authors.initials: RM
authors.lastname: Rennebohm
authors.forename: Jeanne E
authors.initials: JE
authors.lastname: Hicks
authors.forename: Carol B
authors.initials: CB
authors.lastname: Lindsley
authors.forename: Maria D
authors.initials: MD
authors.lastname: Perez
authors.forename: Lawrence S
authors.initials: LS
authors.lastname: Zemel
authors.forename: Carol A
authors.initials: CA
authors.lastname: Wallace
authors.forename: Susan H
authors.initials: SH
authors.lastname: Ballinger
authors.forename: Murray H
authors.initials: MH
authors.lastname: Passo
authors.forename: Ann M
authors.initials: AM
authors.lastname: Reed
authors.forename: Ronald M
authors.initials: RM
authors.lastname: Summers
authors.forename: Patience H
authors.initials: PH
authors.lastname: White
authors.forename: Ildy M
authors.initials: IM
authors.lastname: Katona
authors.forename: Frederick W
authors.initials: FW
authors.lastname: Miller
authors.forename: Peter A
authors.initials: PA
authors.lastname: Lachenbruch
authors.forename: Lisa G
authors.initials: LG
authors.lastname: Rider
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D004185:Disability Evaluation; D006801:Humans; D009043:Motor Activity; D009220:Myositis / Q000175:diagnosis* / Q000503:physiopathology; D015588:Observer Variation; D017063:Outcome Assessment, Health Care; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012720:Severity of Illness Index