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Physical therapists can make important contributions to the care of children with inherited neuromuscular disorders. These conditions include Duchenne muscular dystrophy (DMD), a muscle disorder; spinal muscular atrophy, an anterior horn cell disorder; Charcot-Marie-Tooth disease, a neuropathic disorder; and many other congenital and/or pediatric forms of muscular dystrophies and neuropathies. Common elements are their (1) genetic/inherited etiology, (2) progressive nature, (3) primary impairment of muscle weakness, (4) resulting activity limitations and participation restrictions, and (5) secondary complications leading to increased morbidity and mortality. However, they differ in their (1) associated impairments of body structures and functions, (2) secondary complications, (3) natural history, (4) prognosis, and (5) medical management.
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DMD is the most common inherited muscle disease of childhood. It is an X-linked inherited disorder with an incidence of 1.4 to 2 per 10,000 male births (Romitti et al., 2015). A survey of four states in the United States documented a prevalence of 1.3 to 1.8 per 10,000 males ages 5 to 24 years (Centers for Disease Control and Prevention, 2009). A third of the cases arise from new mutations and, therefore, may not have a family history of the disorder. Although this condition mainly affects boys, it is possible for a female to be a manifesting carrier and have signs and symptoms of the disease with varying severity.
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The gene mutation responsible for DMD is located on the short arm of the X chromosome in the Xp-21 region, affecting the gene that codes for dystrophin. Boys with DMD have an absence of dystrophin, a protein normally present in skeletal muscle, smooth muscle, and the brain. In skeletal muscle, dystrophin is located in the sarcolemmal membrane and plays a role in maintaining the integrity of the muscle fibers as part of the dystrophin-sarcoglycan complex. The absence of dystrophin and associated structural proteins leads to a breakdown of muscle fibers, resulting in progressive weakness and loss of function (Birnkrant et al., 2018; Bushby et al., 2010a; Flanigan, 2014).
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Although DMD is inherited, and the gene defect is present from birth, most boys are typically not diagnosed until 3 to 7 years of age unless there is a family history of the disorder (Ciafaloni et al., 2009). Early motor milestones, such as rolling, sitting, and walking, are usually achieved at expected ages, though some children show delays in ambulation and speech. Some children exhibit marked hypertrophy of the calf muscles referred to as pseudohypertrophy because of the presence of enlarged muscle fibers as well as fat and connective tissue. The symptoms that often lead parents to seek medical attention include difficulty with running, jumping, hopping, climbing stairs, and keeping up with peers in day care, school, and community settings. The primary impairment causing activity limitations in DMD is muscle weakness. All muscles are not affected equally, but there is a predictable proximal-to-distal pattern ...