Muscle Strength and Function Measures in a Multicenter Study of Myotonic Dystrophy Type 1 (DM1): Baseline Impairment and Test-Retest Agreement over 3 Months (P5.455)

Objective: To examine the feasibility and reliability of assessing muscle function in a multicenter study of individuals with DM1. Background: Few studies of DM1 have examined test-retest agreement of motor function outcomes in a multicenter context. Design/Methods: Clinical evaluators from 6 sites participated in training sessions to standardize procedures for strength and function assessments. Ambulatory adults with non-congenital DM1 were enrolled in a 1 year natural history study. Evaluations included assessments of strength (quantitative muscle testing (QMT) and manual muscle testing (MMT)) and function (6 Minute Walk Test (6MWT), 30 foot go, and time to ascend 4 stairs) at baseline, 3 months and 12 months. Here we report mean values and variance at baseline, and test-retest agreement over 3 months (intraclass correlations, ICCs). Results: Primary evaluators completed training prior to enrollment of patients. The primary evaluators were responsible for training additional evaluators (6) at their site. 113 individuals with DM1 completed the baseline visit and 106 individuals completed the baseline and 3 month visits. The mean overall strength score was 4.29 on the MRC scale (MMT) and 60.1 percent predicted (QMT). Individuals walked a mean of 396 (standard deviation [sd] = 117) meters on 6MWT, performed the 30 foot go in 6.1 (sd=2.8) seconds, and ascended the stairs in 3.4 (sd=2.0) seconds. The 3 month ICCs (range across sites) were: overall QMT 0.93 (0.80 to 0.97), overall MMT (0.95), 6MWT 0.92 (0.82–.99), 30 foot go 0.92 (0.78–0.98), time to ascend 4 stairs 0.90 (0.85–0.97). Lower extremity strength moderately correlated with mobility tests (MMT: 0.62–0.75; p Conclusions: We demonstrated feasibility of an evaluator training program to produce excellent test-retest reliability across multiple sites, and showed cross-sectional associations between strength and functional outcomes. Study Supported by: NIH NS048843 (Wellstone Center), Muscular Dystrophy Association, Myotonic Dystrophy Foundation, Marigold Foundation, Biogen Disclosure: Dr. Eichinger has nothing to disclose. Dr. Currence has nothing to disclose. Dr. Capron has nothing to disclose. Dr. Duong has nothing to disclose. Dr. Gee has received personal compensation for consulting, serving on a scientific advisory board, speaking, or other activities with Biogen, Ionis. Dr. Gee has received research support from Biogen, Ionis. Dr. Herbelin has nothing to disclose. Dr. Joe has nothing to disclose. Dr. King has nothing to disclose. Dr. Lott has received personal compensation for consulting, serving on a scientific advisory board, speaking, or other activities with PTC Therapeutics. Dr. Myotonic Dystrophy Clinical Re has nothing to disclose.