ABSTRACT
The aim of this chapter is to provide an update on the prevalence, relevance, causes and treatment of fatigue in muscular dystrophies. In a study by McDonald et al., the three problems most frequently cited as “very significant” by patients with slowly progressive neuromuscular disease (n = 811) were muscle weakness (57%), difficulty exercising (43%) and fatigue (40%) (McDonald, 2002). In a study by Kalkman et al., 61% of patients with facioscapulohumeral dystrophy (n = 139) and 74% of patients with myotonic dystrophy (n = 322) were “severely fatigued” (Kalkman et al., 2005). The muscular dystrophies are an inherited group of more than 30 distinct progressive disorders resulting from defects in a number of
genes required for normal muscle structure and function. They are characterised by progressive loss of muscle strength and integrity and they have a variable distribution and severity (Emery, 2002). We will, however, limit our review to those main types of diseases which are most frequent: Duchenne and Becker muscular dystrophy, myotonic dystrophy type 1, facioscapulohumeral muscular dystrophy and the limb girdle muscular dystrophies. A more extensive overview of muscular dystrophies can be found in Engel and Franzini-Armstrong (2004). In this chapter, we will distinguish two main types of fatigue (Table 10.1). Physiological fatigue, or muscle fatigue, has been defined as a reduction in maximal voluntary muscle force (MVC) during exercise. Experienced fatigue, on the other hand, is the subjective feeling of fatigue. Muscle fatigue is not necessarily accompanied by experienced fatigue, or vice versa. High-quality studies about fatigue in muscular dystrophy are scarce. Nevertheless, after a general introduction on muscular dystrophies, addressing both clinical and pathophysiological aspects, the prevalence of experienced fatigue in muscular dystrophies in the literature will be critically reviewed and the putative underlying pathophysiological mechanisms of muscle fatigue and experienced fatigue will be outlined. Finally, literature about treatment of muscle fatigue and experienced fatigue in muscular dystrophies will be reviewed and recommendations for future research will be made. Throughout the chapter, the scientific knowledge will be illustrated by a clinical case report that describes the experienced fatigue of a 59-year-old man with facioscapulohumeral dystrophy, Mr A.
