Measurement and prevention of muscle atrophy in acute spinal cord injury

© 2017 Dr. Maya Goudy PanissetTraumatic spinal cord injury (SCI) is a devastating event, resulting in rapid and extensive deterioration of musculoskeletal tissue due to denervation, which further progresses due to lifelong paralysis. Secondary sequelae of muscle atrophy, such as diabetes, heart disease and osteoporosis contribute to a profile of premature aging in this population. The aims of this program of research were to 1) describe changes in musculoskeletal tissue after spinal cord injury, and the manner and mechanisms by which they might be affected by early exercise, 2) analyze the current evidence regarding the effects of early exercise after SCI, 3) compare and contrast different methods of measuring muscle changes, 4) determine the effects on muscles and body composition of exercise commenced within four weeks after traumatic SCI, and 5) examine the validity of bioelectrical impedance methods to assess body composition in acute SCI. Passive Cycling (PC) and Functional Electrical Stimulation Cycling (FESC) have shown benefits in chronic SCI, but it is unknown how early after injury these interventions may be safely applied. A systematic review was undertaken to critically assess the current evidence on the efficacy of exercise initiated early after traumatic SCI. Eleven studies provided level II evidence showing positive effects of early exercise on muscle, possibly related to load intensity of the protocol. A randomised controlled trial (SCIPA Switch-On) was conducted to determine the safety and relative effectiveness of FESC and PC initiated within four weeks. The results were unable to detect a significant benefit on thigh muscle cross-sectional area of one intervention over the other. However, these results were explained in part by a) lack of statistical power to detect between-group differences, b) a concomitant neurological recovery of lower limb motor function in some participants in both groups, and c) and unexpected positive effects on some participants in the PC group. A novel and salient finding of the study was promising, in that thigh muscle atrophy was attenuated in both groups, relative to expectations if the intervention had had no trophic or anti-catabolic effect (2). Three quarters (75%) of the participants in both groups experienced < 30% reduction in thigh muscle CSAmax, signifying an attenuation of muscle atrophy against previous reports (2-4). Exploratory analysis of changes in muscle volumes found that 9-13 weeks of FESC resulted in higher whole thigh volumes than PC for most participants. Furthermore, hypertrophy of hamstrings and quadriceps volume was moderately and significantly correlated with frequency of FESC, and to a lesser extent, frequency of PC. Lastly, a groundbreaking interdisciplinary observational study was undertaken to validate the use of bioelectrical impedance analysis (BIA), a bedside measure of FFM, against the ‘gold standard’ deuterium dilution method, for measurement of body composition in acute SCI. The data showed that although predictive equations from BIA are population-specific and most published equations are not valid in acute SCI, one equation (5) was able to predict FFM in acute SCI with minimal bias (0.6kg) for group means. However, due to a dispersion of ±5.1kg, further study is needed to validate this measure for clinical evaluation of individuals. This finding is clinically relevant because gold-standard measures of FFM were able to predict total energy requirements (TEE) better than currently used clinical dietetic predictive equations. Thus, BIA, a clinically feasible and valid bedside measure of FFM could provide, for the first time, an objective tool to guide dietetic practice, pending replication of the study, ideally with a larger sample size. In conclusion, the findings of this thesis indicate that a) BIA is an accurate, though possibly imprecise, measure of FFM in acute SCI, and b) supervised FESC and PC interventions are not harmful, and are potentially beneficial, and may be utilized in the clinical setting for medically stable patients with acute SCI. Within the field of rehabilitation, is it imperative to explore and document the practical details and effects of exercise interventions initiated early after SCI, as this thesis has endeavoured to do, for this establishes a critical foundation upon which to build evidence-based practice that endeavours to achieve excellent patient outcomes