Muscle and bone health in adult males with muscular dystrophy

Smith, Jonathan (2015) Muscle and bone health in adult males with muscular dystrophy. Masters by Research thesis (MSc), Manchester Metropolitan University.

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Abstract

Muscular Dystrophy (MD) results in muscle atrophy, loss of ambulation and reduced physical activity through chronic inflammation leading to muscle damage and derangement of muscle physiology. Reduced physical activity relating to muscle weakness and reduced muscle anatomical cross-sectional area (ASCA) due to atrophy lead to a reduction in tensile and compression strain required to maintain bone mineral density (BMD), resulting in adverse bone health. Studies have demonstrated reductions in BMD and muscle size, primarily in children with Duchenne Muscular Dystrophy (DMD) – a severe variant – however there is no extant data describing muscle size in adults with MD, and data describing BMD in adults with other variants of MD is sparse (e.g. Becker‟s (BeMD), Limb Girdle (LGMD), and Fascioscapluohumeral dystrophy (FSHD)). The aim of this study was to measure BMD, tibialis anterior (TA) muscle ASCA, grip strength and physical activity in adult male individuals with four distinct variants of MD compared to unaffected adult male controls. TA ASCA was measured via B-mode ultrasound; BMD was measured using speed-of-sound ultrasound of midshaft Tibia (MST) and distal Radius (DR). Grip strength was assessed through isometric dynamometer contraction; and physical activity through use of two questionnaires. 40 adult males with MD and 10 unaffected male controls were measured for demographic information, T- & Z-scores of BMD, TA ASCA, maximum grip strength and physical activity. BMD assessed by Z-score was lower in DMD individuals compared to all other participants in tibia and radius and lower in BeMD and FSHD individuals compared to CTRL (P<0.05). There was no difference in T or Z scores between CTRL and LGMD participants. TA ASCA was smaller in all MD individuals compared to controls (BeMD -39.7%; DMD -59.7%; FSHD -58.9%; LGMD -62.4%) (P<0.05). Physical activity was lower in DMD individuals compared with all other MD individuals (assessed by the Bone-specific Physical Activity Questionnaire) (P<0.05) and all MD groups demonstrated significant reductions in grip strength compared to control (BeMD -51.2%; FSHD -46.3%; LGMD -49.9%) (P<0.05). In conclusion, decreased TA ASCA was observed in all MD individuals and reduced T and Z scores observed in three of four groups compared to controls. MD individuals demonstrated reduced physical activity and grip strength compared to controls. Due to the link between BMD and physical activity it is recommended that efforts be made to encourage weight bearing activity and exercise in individuals with MD and that future research investigate the specific benefits of physical exercise in MD individuals to establish best practice for healthcare professionals.