Sarcopenia in very old persons : a study of the relationship between muscle mass, muscle strength, physical performance and adverse events

Sarcopenia is defined by a loss of muscle mass and strength with aging. Many factors have been reported to intervene in this process including physical activity, nutritional status, hormonal status and higher levels of serum inflammatory markers. The main consequences of sarcopenia are limitations of physical performance in older people which increases the risk of falls, fractures, hospitalizations, dependency and mortality. The prevalence of sarcopenia varies widely between studies especially in people older than 80 years (range 10-50%). This large variability results from the different criteria that are used in these studies to define Sarcopenia. Recently, the International Working Group on Sarcopenia suggested that firstly the presence of sarcopenia should be evaluated in all patients with observed declines in physical functional, strength or health status. Secondly, the diagnosis of sarcopenia should be based on gait speed and muscle mass (12). However, it has been suggested that in subjects aged 80 years and older, muscle strength and physical performance capacity may be more relevant indicators of sarcopenia than the muscle mass index (15, 16, 21). The aim of this thesis is to investigate Sarcopenia in very old persons throughout following questions: ”What is the prevalence in community-dwelling very older persons in Belgium?”, “What is the relationship between muscle mass, muscle strength, inflammatory markers and physical performance?”, “What are the predictive values of muscles strength and physical performance for all-cause mortality, hospitalization and the onset of disability, independent of muscle mass, inflammation and comorbidity?” and “What are relevant cut-off points of grip strength and physical performance to detect a clinically significant risk in this population?”. Our results showed that 12.5% of the participants in the study were regarded as sarcopenic, according to the European consensus. The strong discrepancy between the prevalence of low muscle mass and the prevalence of low grip strength or poor physical performance was confirmed in our study. The prevalence of sarcopenia according to single criteria was estimated for men and woman respectively to be 14.6 and 12.4% according to skeletal muscle index, 49.5 and 59.5% according to grip strength criterion, 44.7 and 70.8% according to Short physical performance battery (SPPB) and 81.6 and 96.2% according to gait speed. In addition, this study showed that the European consensus does not provide much additional value to determine the prevalence of sarcopenia compared to the use of a single measurement of muscle mass. This study showed that the grip strength is associated with low physical performance in very old people and support the hypothesis that low physical performance levels are associated with low grip strength levels rather than with low muscle mass. Low physical performance was only associated with low grip strength in both sexes and in women with age and comorbidities. No association with inflammatory markers was observed. In people aged 80 and over, physical performance is a strong predictor of mortality, hospitalization and disability. Muscle strength, on the other hand, is as a strong predictor of mortality and hospitalization. Moreover, all these relationships were independent of muscle mass, inflammatory markers and comorbidity. The current study could not find a significant association between the activities of daily living scale decline and muscle strength. In contrast physical performance showed a significant relationship with activities of daily living scale decline, even after adjusting for potential confounders. Cut-off values to identify an early risk of poor mobility or an onset of disability were estimated for women as 20.3 kg for grip strength and 8 for SPPB and for men as 31.5 kg for grip strength and 8 for SPPB. Cut-off values 20.4 kg for grip strength and 4 for SPPB test have been identified as a strong predictor of mortality in very older women. For men, cut-off values of 26.5 for grip strength and 6 for SPPB were identified as a strong predictor of mortality. Moreover, all these relationships were independent of muscle mass, the activities of daily living capacity, the 15-item Geriatric Depression Scale, the cognitive status and comorbidities. In conclusion, ours results shown that use of easily available tools in clinical practice like grip strength and physical performance test are good risk predictors; better than the muscle mass to predict adverse outcomes such as mortality and hospitalization in subjects aged 80 and older. A new approach diagnosis of sarcopenia could be developed based on muscle strength and function and adapted for very old persons in community-dwelling and clinical practice. In addition, our findings confirmed that the current cut-off values permit to predict a risk of poor mobility in community-dwelling population.