Maarten van Egmond

67 The association of muscle strength with muscle mass 4 INTRODUCTION Esophagectomy is the primary option for curative treatment in patients with esophageal cancer and is associated with a high rate of mortality and morbidity. 1,2 A majority of these patients will be confronted with dysphagia and weight loss during the course of their disease. 3-5 This may lead to decreased muscle mass and muscle strength and eventually to sarcopenia, a multifactorial syndrome characterized by chronic inflammation, inactivity, malnutrition and weight loss which leads to decreased muscle mass and general loss of muscle function, leading to adverse outcomes such as increased complication rates, delayed functional recovery, low quality of life and high mortality. 6-10 A loss of muscle mass may reflect high metabolic stress due to systemic inflammation in patients with esophageal cancer. The imbalance between anabolic and catabolic activity within muscle leads to a loss of muscle mass with increased muscle protein degradation as a consequence. 11 Hormones, tumor-derived factors, inactivity and malnutrition also contribute to a loss of muscle mass, negatively affecting the metabolic response to gastrointestinal surgery and increasing the risk of complications following surgery. 12 The prevalence of sarcopenia in patients with esophageal cancer awaiting neoadjuvant chemoradiation varies between 47 and 57% increasing from 53% to 79% after neoadjuvant chemoradiation. 13,14 Moreover, sarcopenia is an independent predictor of postoperative pulmonary complications, because it does not only affect general muscle strength, but also respiratory muscle strength. Reduced respiratory muscle strength leads to an ineffective cough and increases the risk of postoperative pneumonia and atelectasis. 3,10,13 Therefore, it is important to assess patients on decreased muscle mass and muscle strength before neoadjuvant chemoradiation, since early tailored exercise therapy and nutritional support may prevent patients from developing sarcopenia with consequences for functional performance. 15 To diagnose decreased muscle function, both muscle mass and muscle strength need to be assessed. 9 Muscle mass is usually measured with dual x-ray absorptiometry (DXA), computed tomography (CT), or magnetic resonance imaging (MRI). 16,17 Physiotherapists are unable to measure muscle mass directly, but they are able to quantify aspects of muscle strength and endurance by hand held dynamometry and muscle strength measures. The association between muscle mass and muscle strength is not self-evident because, although the loss of muscle mass is associated with the decline in muscle strength, muscle strength decline may be more rapid than the loss of muscle mass, while muscle mass is maintained or even increased. 18,19 Many studies have shown an association between muscle mass and muscle strength, but there are no studies that investigated this association in patients with esophageal cancer scheduled for esophagectomy. 18-21