A New Functional Scale and Ambulatory Functional Classification of Duchenne Muscular Dystrophy: Scale Development and Preliminary Analyses of Reliability and Validity

OBJECTIVE: To develop a simplified functional scale and classification system to evaluate the functional abilities of patients with Duchenne muscular dystrophy (DMD). METHODS: A Comprehensive Functional Scale for DMD (CFSD) was developed using the modified Delphi method. The accompanying Ambulatory Functional Classification System for DMD (AFCSD) was developed based on previously published classification systems. RESULTS: The CFSD consists of 21 items and 78 sub-items, assessing body structure and function, activities, and participation. Inter-rater intraclass correlation coefficient values were above 0.7 for 17 items. The overall limits of agreement between the two examiners ranged from -6.21 to 3.11. The Spearman correlation coefficient between the total score on the AFCSD and the Vignos Functional Scale was 0.833, and 0.714 between the total score of the AFCSD and the Brooke scale. Significant negative correlations existed between the total score for each functional level of the AFCSD and each functional grade of the Vignos and Brooke scales. The total scores of the CFSD varied significantly between the functional grades of the Vignos scale, and specific grades of the Brooke scale. For the AFCSD, total scores of the CFSD varied significantly between the functional levels. CONCLUSION: We have developed a new scale and the associated classification system, to assess the functional ability of children diagnosed with DMD. Preliminary evaluation of the psychometric properties of the functional scale and classification systems indicate sufficient reliability and concurrent validity.