Skeletal muscle abnormalities and outcomes after liver transplantation

Muscle depletion or sarcopenia in cirrhosis is part of the frailty complex present in these patients, and it is characterized by a decreased reserve and resistance to stressors resulting from cumulative declines across multiple physiologic systems and a predisposition to poor outcomes. In addition, muscle depletion is characterized by both a reduction in muscle size and an increased proportion of intramuscular fat, which is called myosteatosis. Myosteatosis increases with age and adiposity and is associated with systemic metabolic abnormalities and decreased strength and mobility. At present, several methods are available for evaluating the body composition and muscle mass estimation of patients with cirrhosis; they include total body electrical conductivity, bioelectrical impedance, dualenergy X-ray absorptiometry, air displacement plethysmography, and magnetic resonance spectroscopy. However, most of these techniques have limitations, primarily a lack of objectivity and reproducibility. In this respect, muscularity assessment based on crosssectional imaging studies [computed tomography (CT) scanning or magnetic resonance imaging] has become an attractive index for nutritional status evaluation in cirrhosis. The analysis is not biased by the fluid overload status or obesity that frequently presents with cirrhosis, and muscle abnormalities reflect a chronic detriment in the general physical condition rather than acute severity of the liver. In this issue of Liver Transplantation, Hamaguchi et al. report the impact of the preoperative quality of skeletal muscle on outcomes after living donor liver transplantation (LDLT). They evaluated the intramuscular adipose tissue content (IMAC) in multifidus muscle and the psoas muscle mass index (PMI) via CT analysis in adult patients undergoing LDLT. In male patients, a positive correlation was observed between IMAC and age, and a negative correlation was observed between IMAC and PMI; in females, a positive correlation was observed only between IMAC and age. Survival rates for patients with high IMACs or low PMIs were significantly lower than those for patients with normal IMACs or PMIs. Multivariate analysis showed that a high IMAC and a low PMI were independent risk factors for mortality after LDLT. This study by Hamaguchi et al. emphasizes that muscle abnormalities such as sarcopenia and myosteatosis are frequent complications in cirrhosis and, despite the important role that they play in the prognosis of cirrhosis, are frequently overlooked. Some notes of caution are in order. One important issue to be resolved is which technique is better for muscularity assessment in patients with cirrhosis. For the evaluation of sarcopenia, some studies have used the total psoas area (TPA) or PMI at the level of the umbilicus. However, to the best of my knowledge, there is actually no evidence confirming that the area of the psoas muscle or the PMI has a good correlation with the whole lumbar or whole body muscle areas. Moreover, the location of the umbilicus may change in patients with ascites, so measures may be recorded at different levels in these patients. In light of this potential limitation, our group has used the third lumbar skeletal muscle index (L3 SMI), which has been shown to be the best single imaging correlate of whole body muscle mass (Fig. 1A). Also, we have