Myopathies are diseases characterized by primary muscle pathology.¹ They can be inherited, acquired, associated with other diseases, or result from toxic exposures. The primary clinical manifestation of a myopathy is weakness, and accompanying symptoms can include (but are not limited to) wasting, cramps, spasms, myoclonus, contractures, and fatigue. Endurance and functional capacity are limited to varying degrees in different classes of myopathies. The pattern of weakness, constellation of associated symptoms, nature of progression, and other organ involvement together can point to a specific diagnosis (see Fig. 75–1).

An accurate diagnosis is important because it helps the clinician to develop appropriate management strategies.¹ In this chapter, we will focus on the myopathies that are most likely to be seen by practicing physiatrists including muscular dystrophies, myotonic dystrophy, inflammatory myopathies, congenital myopathies, and critical illness myopathy. While a detailed description of these and other rare muscle disorders is beyond the scope of this chapter, it is important for physiatrists to be familiar with rehabilitation interventions that can greatly impact the quality of life of these patients.

The physiatrist plays an essential role in helping patients maintain function as much as possible and adapt to changes over time as muscle weakness progresses.² Physiatrists also coordinate appropriate rehabilitation services as needed and provide guidance about equipment needs and timing. The rehabilitation team also connects patients and families with community support resources and services.

The primary rehabilitation goals for patients with muscle disease include engagement in the most appropriate exercise program, provision of appropriate bracing, mobility equipment, and assistive devices for completing activities of daily living, maintenance of independence to the greatest extent possible, education of patient and family about disease trajectory and expectations, and facilitation of patient autonomy in decision-making.² Physiatrists can also link patients with clinical studies as appropriate and foster collaboration with multiple medical and rehabilitation specialties to provide a coordinated medical home for patients and families.²

The muscular dystrophies are a group of genetic disorders that cause degeneration of muscle and replacement of muscle with fat and connective tissue.¹ The more common muscular dystrophies are Duchenne muscular dystrophy (DMD), Becker muscular dystrophy (BMD), facioscapulohumeral muscular dystrophy (FSHD), limb girdle muscular dystrophy (LGMD), Emery-Dreifuss muscular dystrophy (EDMD), and oculopharyngeal muscular dystrophy (OPMD).¹

At the molecular level, most dystrophies result from dysfunction or functional absence of key muscle molecules in the dystrophin-glycoprotein complex. This results in weakening of the sarcolemma, muscle necrosis, fatty replacement, and weakness. When the weakness affects respiratory or cardiac muscles, the weakness can be life-threatening (see Fig. 75–2).

Genetic transmission, inheritance pattern, protein defect, age of onset, and average age of onset for daily wheelchair use are listed in Table 75–1.

Epidemiology and Clinical Presentation

As X-linked disorders, DMD and BMD both manifest in boys. DMD is more severe with earlier age of onset (see Table 75–1), and more prevalent than BMD. DMD is more common and affects 1 out of every 3,500 boys.³ Patients may present initially with a waddling gait, toe walking, noticeable lordosis, easy trips/falls, difficulty rising from the ground, or easy fatigue.¹ In both DMD and BMD, proximal weakness is greater than distal weakness. Lower extremities tend to be affected more than the upper extremities, and there is typically heart and diaphragmatic muscle weakness.¹ Calf muscles can show pseudohypertrophy due to fatty replacement of muscle tissue (see Fig. 75–3).

A Gower sign can be present, although not specific for DMD/BMD (a positive Gower sign reflects weak proximal lower extremity muscles and occurs when a patient walks his arms up his legs when changing position from squatting to sitting, to compensate for weak proximal hip and thigh muscles; see Fig. 75–4) There can be intellectual disability and speech/language in DMD, and, to a lesser extent, in BMD.

Lab Testing

Creatine kinase (CK) is elevated and can be as high as 50 to 100 times the upper limit of normal. CK typically peaks early in the disease course and then declines over time as muscle mass is lost.⁴ In the appropriate clinical context, genetic testing is the best diagnostic test to confirm DMD and BMD.⁵ Occasionally, genetic tests are inconclusive and a biopsy can help confirm the diagnosis. Needle EMG typically demonstrates increased spontaneous activity in the form of fibrillations and positive sharp waves, as well as small, brief motor unit action potentials (MUAPs).⁶

Management

Currently, the primary medical treatment for DMD is corticosteroids, which can delay (but not prevent) the onset of wheelchair use.^7,8 Not all families opt to use steroids, due to side effects of weight gain, sleep impairment, and behavioral changes.⁹ The field of medical treatments is rapidly expanding, with a number of very promising agents currently in clinical trials.¹⁰ Recently, an exon skipping method was approved for subsets of DMD patients carrying certain mutations.¹¹ Exon skipping methods allow for a mutated exon to be skipped so that a shortened but functional form of dystrophin can be produced. Cardiac and pulmonary management for associated cardiomyopathy and progressive respiratory impairment are mainstays of treatment. Prevention of osteoporosis with vitamin D supplementation is also generally common practice.

Long-term management for DMD and BMD is supportive care.^12,13 Early bracing, along with stretching and splinting for upper and lower extremities can prevent contractures and preserve function.¹⁴ In order to optimize compliance, orthotics chosen should be lightweight and easy to don and doff. Family education regarding proper techniques for use of orthotics is important to assure that the devices are used safely and effectively. Exercise is generally considered safe at a submaximal level to the extent tolerated for boys with DMD and BMD.^15,16 As with all neuromuscular diseases, exercise should be limited by extreme fatigue or muscle cramps/soreness.

Initially, boys with DMD may benefit from walkers, but limited endurance from both cardiorespiratory and muscle factors typically leads to fairly rapid onset of wheelchair use for energy conservation. Arm weakness and easy fatigue make manual wheelchairs of limited utility. A power wheelchair should be fitted and prescribed after recommendations from a physical therapist with expertise in wheelchair prescription for people with neuromuscular disease. For example, the wheelchair should be modifiable to accommodate patient growth and allow room for potentially adding a ventilator, and the back should be chosen to accommodate lordosis, scoliosis, or other spinal deformity. The drive controls need to be reevaluated as the child with DMD progresses. A simple joystick may work well initially but not be the best option as upper extremity weakness progresses.¹⁷ The child’s cognitive capacity should also be considered when adding features. For example, if parent or guardian assistance in driving the chair is required, a rear mount joystick can be helpful. In addition, a child should also be given the autonomy to select features such as color.

As diaphragmatic and respiratory muscle weakness progresses, patients and family must make challenging decisions about plans for respiratory support (both noninvasive and, eventually, tracheostomy and long-term mechanical ventilation).¹⁸ Anticipating future needs with families before a crisis/emergency is a key component to DMD/BMD care. Decision making occurs best between a provider and family who know each other well; such a relationship allows for decisions to be made over the course of several conversations. A physiatrist can have these conversations alone with a family or in collaboration with pulmonology and palliative care, keeping in mind that every family makes decisions with a unique set of values, in its own time frame, and with differing goals. It is important to elicit a family’s goals for care, including previous experiences that may impact care decisions, and to help families to make safe decisions for a patient consistent with the patient and family’s goals and values.¹⁹

Additional needs of patients with DMD and BMD can include management of dysphagia, reflux, constipation, aspiration, and osteoporosis (from both steroids and lack of weight bearing), as well as monitoring for scoliosis. Neuromuscular scoliosis in DMD and BMD cannot be slowed by bracing, and spinal fusion is often considered as an early intervention to arrest progression.²⁰

Physiatrists also interface with schools and teachers to offer guidance on optimizing school accessibility and advocating for in-school services as necessary (e.g., physical therapy, occupational therapy, speech language pathology, educational specialist, nursing).

Epidemiology and Clinical Presentation

The most common form of EDMD is X-linked recessive with a mutation that results in a lack of nuclear membrane protein (Emerin). There are also autosomal dominant and recessive forms of the disease due to mutations in other genes. The prevalence of EDMD is estimated to be 0.1/100,000²¹ and onset ranges from childhood to adulthood with most typical onset in the teenage or young adult years. Typical clinical features include muscle contractures disproportional to the degree of muscle weakness, particularly in the heel cords and elbow flexors, as well as cervical and lumbar paraspinal muscles.¹ Weakness typically presents in the upper extremity muscles with prominent wasting in the biceps brachii, as well as the posterior calf muscles. Hip and shoulder girdles can be affected later in the disease trajectory. There can be toe walking (from ankle dorsiflexor weakness).¹ Unlike DMD and BMD, there is typically no calf pseudohypertrophy.

Importantly, EDMD also presents with dilated cardiomyopathy with conduction abnormalities which can cause arrhythmias and sudden cardiac death. For this reason, patients need to be evaluated at least once per year by a cardiologist for monitoring and potential implantable cardioverter-defibrillator (ICD) placement.²² Severity of EDMD varies between families, and even within families, and prognosis generally is most impacted by the degree of cardiac involvement.

Lab Testing

CK is often normal to mildly elevated.²³ Needle EMG shows a myopathic pattern.⁶ Genetic testing can confirm the diagnosis.^24,25

Management

Medical treatment of EDMD includes yearly EKGs to screen for conduction abnormalities.²⁶ Mainstays of rehabilitation management include physical and occupational therapy to optimize function and active lifestyle, guide bracing fit and usage, recommendation on appropriate safety and mobility strategies, and collaboration with physiatrists and orthopedic surgeons for contracture management. Daily stretching and bracing are attempted for contracture prophylaxis / early contracture management, positioning, comfort, and facilitating good hygiene. These techniques may not be fully effective. If severe and function-limiting contractures develop, surgical correction can be utilized.²⁷ Post-procedure stretching, bracing, pain management, physical therapy, modification of mobility devices, patient education, and scheduled follow-up are key components to these orthopedic procedures.

Epidemiology and Clinical Presentation

FSHD is a slowly progressive muscular dystrophy with autosomal dominant transmission. Muscle damage is believed to result from overexpression of muscle-toxic DUX4 protein.²⁸ FSHD is one of the most common muscular dystrophies, and worldwide prevalence is estimated to be 1/7500, with many additional cases that go undiagnosed.²⁹

Clinical presentation is heterogeneous.¹ Classic presentation in a young adult is difficulty with overhead activities. On physical examination, early in the disease course, an individual with FSHD may demonstrate asymmetric weakness of the facial muscles, scapular stabilizers, external rotators, and elbow flexors. Findings include inability to completely close the eye against resistance, an inability to whistle, and scapular winging (see Fig. 75–5).

Weakness of trunk and abdominal muscles, as well as lower extremity muscles (tibialis anterior, hamstrings, pelvic girdle) may also be present initially or develop over time. A positive Beevor’s sign may be found on exam (umbilicus moves upward when supine patient lifts head; results from disproportionately strong upper as compared with lower abdominal muscles). Up to one third of people with FSHD ultimately use wheelchairs for safety and mobility due to pelvic girdle and lower extremity weakness.

Lab Testing

CK is usually within normal range, although occasionally can be slightly elevated. Nerve conduction studies (NCSs) are within normal range, and EMG shows myopathic findings.⁶ Genetic testing includes evaluation of length and methylation of the D4Z4 repeat site.³⁰

Management

Key features of rehabilitation management in FSHD³¹:

1. 
   

   Safe exercise recommendations (submaximal aerobic and resistance exercises)^32,33; caution should be taken to not overuse weakened muscles that don’t have antigravity strength.

   
   
2. 
   

   Management of weakness (including bracing and gait training for foot drop, abdominal binder for abdominal weakness).

   
   
3. 
   

   Management of scapular winging (including pain management and safe compensation strategies, orthoses, surgical intervention such as scapular fixing when clinically indicated).^34,35

   
   
4. 
   

   Pain management (typical areas of pain are back, shoulders, and hips, due to regional muscle imbalance and compensatory use of unweakened muscles).³⁶

   
   
5. 
   

   Fatigue management (including energy conservation strategies and appropriate adaptive equipment).³⁷

Medical management includes screening and care for respiratory insufficiency (if present). Vision issues and sensorineural hearing loss may be present, especially in infantile-onset cases, where it can interfere with learning and development.³⁰

Epidemiology and Clinical Presentation

The LGMDs are a group of slowly progressive muscular dystrophies characterized by gradual progression of symmetrical hip and shoulder girdle weakness.¹ Onset is typically in the young adult years, although it can range from infancy to adulthood. Severity can be variable, with some patients experiencing a greater degree of disability than others. Evidence-based guidelines for the diagnosis and management of the LGMDs from the American Academy of Neurology and American Association of Neuromuscular and Electrodiagnostic Medicine provide detailed information about the diagnosis and management of the subtypes.³⁸

Of note, there are autosomal dominant LGMDs (LGMD 1) and autosomal recessive (LGMD 2) types, which are further characterized with letters that reflect specific constellations of symptoms (e.g., LGMD 2I typically includes cardiomyopathy and calf hypertrophy).¹ Phenotypic heterogeneity often makes it challenging to arrive at a specific subtype diagnosis on a clinical basis and genetic testing is increasingly used to determine the molecular underpinning of the disease in affected individuals. Certain subtypes are more likely to be associated with respiratory, cardiovascular, and gastrointestinal complications.³⁸

Lab Testing

Depending on the LGMD subtype, CK can be within the normal range, or as high as 15 to 20 times the upper limit of a lab’s normal range. Genetic testing is often performed in affected individuals.³⁸ EMG and needle muscle biopsy (if performed) show myopathic changes.⁶

Management

Overall LGMD management is based on symptom constellation.³⁸ Patients with LGMD could require cardiac interventions for abnormal rhythm, cardiomyopathy, or syncope; support for respiratory insufficiency or respiratory failure; feeding tubes to mitigate dysphagia, aspiration, or weight loss/inability to feed due to arm weakness; monitoring and intervention for spinal deformities that can impair seating, breathing, and comfort; and monitoring and intervention for osteoporosis (osteoporosis is a risk in all mobility-limiting conditions).³⁸ Rehabilitation management includes optimizing mobility, comfort, and use of assistive and mobility devices. Rehabilitation also includes educating each patient and family about anticipated disease trajectory, and planning for expected changes as well as determining goals for end-of-life care and support.