Physical exercise in adults with hereditary neuromuscular disease

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    Hereditary neuromuscular diseases are a heterogeneous group of disorders that may manifest at birth, although symptoms may also emerge in childhood or adulthood. Persons with hereditary neuromuscular diseases have previously been advised to avoid strenuous physical activity for fear that exercise would damage their already weakened muscles. Recent studies show that physical activity and exercise can be beneficial, but must be tailored to individuals on the basis of their diagnosis and functional level.

    This article concerns hereditary myopathies and muscular dystrophies in adults (Table 1), and is based on a discretionary selection of reviews and original articles, as well as the authors' clinical experience with this patient population. All of these neuromuscular diseases predominantly affect skeletal muscle; however, they may affect other organs too, especially the heart (1). The pattern of inheritance may be dominant, recessive or sex-linked (1). Most of the disorders are progressive; some progress quickly whereas others remain relatively stable over time (2). The disease course varies depending on the specific neuromuscular disorder, but major individual differences may be seen even among patients with the same genetic mutation. Much progress has been made in the diagnosis of neuromuscular diseases, and umbrella terms such as limb-girdle muscular dystrophy now include numerous genetically defined subgroups (1). A specific genetic diagnosis can provide insights into the particular challenges associated with a given disease variant. This knowledge is important for being able to offer appropriate guidance and advice on exercise and physical activity.

    Table 1

    Examples of hereditary neuromuscular diseases. AD = autosomal dominant, AR = autosomal recessive

    Disorder type

    Disorder

    Inheritance

    Muscular dystrophies

    Duchenne/Becker

    X-linked

    Emery-Dreifuss

    X-linked AD/AR

    Facioscapulohumeral

    AD

    Limb-girdle

    AD/AR

    Disorders of cell membrane excitability, and myotonias

    Myotonic dystrophies type I and II

    AD

    Congenital myotonia

    AD/AR

    Periodic paralysis

    AD

    Congenital muscular dystrophies/myopathies

    Central core

    AD

    Nemaline

    AD/AR

    Ullrich/Bethlem

    AD/AR

    Distal myopathies

    Welander

    AD

    Distal titinopathy

    AD/AR

    Metabolic myopathies

    McArdle

    AR

    Mitochondrial myopathies

    Mitochondrial inheritance/X-linked/AD/AR

    We know from the normal population that lack of exercise and a sedentary lifestyle can lead to health problems and disease (3). Moreover, physical activity can, to some extent, prevent chronic disease and have a positive effect on conditions such as depression and pain (4). Recommendations have been developed for physical activity both for the general population and for persons in poor health (5). However, this is general advice that does not necessarily apply specifically to individuals with neuromuscular disease (4). We know that lack of physical activity may lead to further loss of muscle mass, reduced walking distance and increased risk of overweight, fatigue and pain in persons with neuromuscular disease (4). An increase in activity levels must be tailored to each individual in accordance with his/her interests, wishes and functional level, and should contribute to a feeling of coping. Physical activity need not be synonymous with organised exercise, but may include everyday activities in which fitness, strength and mobility are challenged with appropriate frequency, duration and intensity (5).

    Complications relevant to exercise

    Complications relevant to exercise

    Weakness, stiffness and contractures

    Weakness, stiffness and contractures

    Neuromuscular disorders are primarily associated with muscle weakness, the distribution of which differs between subgroups (1, 2). A distinction is often made between proximal and distal muscle weakness. In some disorders, there may also be significant weakening of back and abdominal muscles (6). Muscle stiffness (myotonia) is typically seen, especially in myotonic dystrophy, but also in other neuromuscular diseases (2). Contractures are common (7) and occur as a result of an imbalance in the muscles around a joint and a reduced ability to use the muscles. They may also be a consequence of the dystrophic process, as in Emery-Dreifuss muscular dystrophy and Ullrich congenital muscular dystrophy (1). Contractures may result in secondary impairments and difficulties in using otherwise functional muscles.

    Pain and fatigue

    Pain and fatigue

    Pain has been seldom studied in patients with hereditary neuromuscular diseases (7), but is often reported by the patients themselves. Pain may be a consequence of secondary changes such as stiffness or suboptimal movements of the body, but it may also be a hallmark of the disease itself, as in facioscapulohumeral muscular dystrophy (8). Fatigue is another common challenge for patients with neuromuscular disease (7, 9). Exercise of an appropriate type and amount may be beneficial in combatting fatigue (8, 10, 11).

    Elevated creatine kinase levels

    Elevated creatine kinase levels

    Some muscular dystrophies and metabolic myopathies are associated with an increased risk of rhabdomyolysis (2). Rhabdomyolysis is characterised by an acute increase in levels of the muscle enzyme creatine kinase (CK) owing to extensive damage to muscle cells (12). Myoglobin deposition in the kidneys as a consequence of such acute damage may be treated, if necessary, with forced alkaline diuresis (12). In healthy individuals, a CK level > 5 000 IU/l is proposed to indicate treatment-requiring rhabdomyolysis (12). Elevated CK levels ​​are common in neuromuscular disease, although levels may be normal in slowly progressive myopathy and certain muscular dystrophies (2). It is important to be aware that some patients with muscular dystrophies may have significantly increased CK levels without displaying symptoms of rhabdomyolysis. Sensible exercise programmes will not normally lead to dangerous increases in CK levels in patients with neuromuscular diseases. Nevertheless, it is useful to know which variant of hereditary muscle disease a patient has, in order to assess the risk of triggering rhabdomyolysis.

    Cardiac involvement

    Cardiac involvement

    Cardiac involvement is common in some neuromuscular diseases (13). These include many muscular dystrophies (Duchenne, Becker and Emery-Dreifuss muscular dystrophies, myotonic dystrophy types 1 and 2, limb-girdle muscular dystrophy types 1B, 2C–F, 2G and 2I) (13) and certain congenital myopathies (14). Cardiac involvement may manifest as cardiomyopathy or cardiac arrhythmias (14). For some neuromuscular diseases such as limb-girdle muscular dystrophy type 1B (laminopathy), cardiac involvement may be the first and sometimes the only sign of neuromuscular disease (13). The most common variant of limb-girdle muscular dystrophy in Norway, type 2I, may give rise to dilated cardiomyopathy and conduction disease (13). In cases of known or suspected cardiac involvement, therefore, it is important for the patient to be monitored by a cardiologist irrespective of whether or not they have symptoms (13, 14). In neuromuscular diseases known to affect cardiac muscle, it is usually safe to exercise, but advice on physical activity must be given after consultation with a cardiologist and preferably following a cardiac examination (13).

    Respiratory muscle involvement

    Respiratory muscle involvement

    Some neuromuscular diseases affect respiration, mainly as a result of weakening of the respiratory muscles (15). This is the case in some metabolic myopathies and mitochondrial myopathies, as well as in congenital myopathies and a number of muscular dystrophies (Duchenne, Becker, Emery-Dreifuss and facioscapulohumeral muscular dystrophy, myotonic dystrophy type 1, and limb-girdle muscular dystrophy types 2A and 2I) (2). Endurance training, strength training and training of respiratory muscles can be helpful, and studies have shown improvements in daily activities, quality of life and oxygen uptake (VO2 max) (15). It has been shown that aerobic exercise and strength training are likely to be effective in patients with neuromuscular disease, and that cardiovascular changes due to exercise are comparable with those seen in healthy persons (15). Respiratory training in neuromuscular diseases is somewhat controversial and requires specific knowledge of pulmonary physiotherapy and of the particular neuromuscular disorder in question (15). In cases of severe restrictive pulmonary impairment, it is not certain that respiratory training is beneficial, and it is important to be familiar with various breathing aids (15).

    Summary

    Summary

    Our recommendation is to avoid the inactivity that would otherwise lead to increased deconditioning and further reduction in muscle strength beyond that caused by the primary neuromuscular disease. Such deconditioning and loss of strength may in turn increase fatigue and pain, and decrease mobility and functioning. Appropriate training and physical activity is generally safe, but must be tailored to the individual on the basis of his/her diagnosis, functional level and lifestyle.

    Tailored physical activity that takes into account disease-specific issues is recommended as it may facilitate daily activities and improve physical fitness. For advice on appropriate forms of activity, it may be useful to consult a physiotherapist with knowledge of neurology and experience in creating personalised exercise plans with appropriate amounts and types of training.

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