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Two-Year Longitudinal Changes in Lower Limb Strength and Its Relation to Loss in Function in a Large Cohort of Patients With Duchenne Muscular Dystrophy

Batra, Abhinandan, PT, MA, PhD; Harrington, Ann, PT, DPT, PhD; Lott, Donovan J., PT, PhD, CSCS; Willcocks, Rebecca, PhD; Senesac, Claudia R., PT, PhD; McGehee, William, PT, PhD; Xu, Dandan, PhD; Mathur, Sunita, PT; Daniels, Michael J., ScD; Rooney, William D., PhD; Forbes, Sean C., PhD; Triplett, William, BS; Deol, Jasjit K., PT; Arpan, Ishu, PT, PhD; Bendixen, Roxanne, PhD; Finkel, Richard, MD; Finanger, Erika, MD; Tennekoon, Gihan, MBBS, MRCS, LCRP; Byrne, Barry, MD, PhD; Russman, Barry, MD; Sweeney, H. Lee, PhD; Walter, Glenn, PhD; Vandenborne, Krista, PT, PhD

American Journal of Physical Medicine & Rehabilitation: October 2018 - Volume 97 - Issue 10 - p 734–740
doi: 10.1097/PHM.0000000000000957
Original Research Articles

Objective The main objective of this study was to examine the effect of disease on strength in two functionally important lower limb muscles for a period of 2 yrs in children with Duchene muscular dystrophy.

Design Seventy-seven Duchene muscular dystrophy children participated in this study. Plantar flexors, knee extensors, strength, and performance on timed tests (6-min walk, 4-stairs, 10-m walk, supine-up) were assessed yearly for 2 yrs. Multivariate normal regression was used to assess changes in strength over time in the Duchene muscular dystrophy group. Spearman correlations were computed to examine relationship between strength and function.

Results Normalized plantar flexor and knee extensor strength showed a significant decrease (P < 0.05) over 2 yrs, with larger declines in knee extensor. At baseline, knee extensor strongly correlated with performance on timed tests. However, plantar flexor strength was found to be a stronger predictor of loss in ambulatory function. Modest correlations (r = 0.19–0.34) were found between the decline in strength and functional performance over 2 yrs.

Conclusions This study describes the loss of lower limb strength in a large cohort of Duchene muscular dystrophy children for 2 yrs. The findings support that lower limb strength alone cannot account for the decline in performance on functional tests, and the role of other contributing factors, such as compensatory strategies, should be considered.

From the Department of Physical Therapy, University of Florida, Gainesville, Florida (AB, DJL, RW, CRS, WM, SCF, WT, JKD, KV); Department of Physical Therapy, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania (AH); Department of Statistics, University of Florida, Gainesville, Florida (DX, MJD); Department of Physical Therapy, University of Toronto, Toronto, Ontario, Canada (SM); Advanced Imaging Research Center, Oregon Health and Science University, Portland, Oregon (WDR); Department of Neurology, Oregon Health and Science University, Portland, Oregon (IA); Department of Occupational Therapy, School of Health and Rehabilitation Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania (RB); Department of Pediatrics, Nemours Children's Hospital, Orlando, Florida (RF); Department of Pediatrics, Oregon Health and Science University, Portland, Oregon (EF); Division of Neurology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania (GT); Department of Pediatrics, University of Florida, Gainesville, Florida (BB); Division of Neurology, Oregon Health and Science University, Portland, Oregon (BR); Department of Pharmacology and Therapeutics, University of Florida, Gainesville, Florida (HLS); and Department of Physiology and Functional Genomics, University of Florida, Gainesville, Florida (GW).

All correspondence should be addressed to: Krista Vandenborne, PT, PhD, Department of Physical Therapy, University of Florida, Box 100154, UFHSC, Gainesville, FL 32610.

The study was supported by Magnetic Resonance Imaging and Biomarkers in Muscular Dystrophy (NIAMS, NINDS: R01 AR056973); First author is supported by Wellstone Grant (NIAMS: U54AR052646).

Abhinandan Batra is in training.

Financial disclosure statements have been obtained, and no conflicts of interest have been reported by the authors or by any individuals in control of the content of this article.

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