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Muscular diseases or myopathies are produced by an alteration in the ability to contract muscles efficiently. Although the motor order is generated in the brain, the last link in the chain is the muscle itself. This motor order passes along the neurones, then the nerves, it interacts with the muscle via the motor end plate and, finally, the muscle contracts itself.
Muscular diseases or Myopathies explained in first person
Professionals and patients explain how you live with the disease
Hereditary diseases today do not have a curative treatment, so most of the treatments are symptomatic. Regarding the acquired ones, 70-80% of inflammatory myopathies have a satisfactory treatment.
Josep Maria GrauMedical internist
Muscular diseases or myopathies are rare diseases where interaction between the different specialists (clinicians, pathologists, geneticists, etc.) is crucial so that the correct diagnosis is made, and there is appropriate monitoring and treatment of the patient. Sometimes, a diagnosis can be made simply by physically examining the patient, but other complementary tests include electromyography, magnetic resonance, measurement of muscle enzymes in the blood, muscle biopsy, forearm ischaemia test, and so on.
The symptoms and signs that usually present with myopathies are muscle weakness, intolerance to exercise, massive muscle breakdown (rhabdomyolysis), pain, atrophy, cramping, muscle spasms, etc.
Muscles are tissues or organs characterised by their ability to contract, and they are divided into skeletal, cardiac, and smooth or visceral.
Skeletal. The human body has over 600 skeletal muscles that move the bones and other structures.
Cardiac. The heart muscle contracts the heart to pump blood.
Smooth or visceral. Smooth muscle tissue forms organs such as the stomach, bladder, uterus, and eye, and changes shape to facilitate bodily functions. Smooth muscle is found in the walls of hollow organs.
Types of Muscular Diseases or Myopathies
Muscle diseases are classified into two main groups:
Those that are not transmitted from parents to children, and which can occur at any age.
Idiopathic Inflammatory Myopathies
Dermatomyositis. This is characterised by proximal muscle weakness, in other words, it affects the muscles that are closest to the central part of the body. Patients often have difficulty getting out of a chair, climbing stairs, or raising their arms above their heads. Skin lesions on the face and hands are also typical.
Inclusion body myositis (IBM). It shows in people over 50 and t is characterised by distal muscle weakness, in other words, it affects the muscles furthest from the central part of the body, such as the quadriceps and the flexors of the fingers.
Immune-mediated Necrotising Myopathy (IMNM). This is characterised by rapid onset proximal muscle weakness.
Antisynthetase syndrome (AS). This is characterised by proximal weakness, involvement of the lungs (inflammation or fibrosis), and arthritis (inflammation of the joints), although not all patients have all three symptoms. Patients may also have a fever, Raynaud's phenomenon (colour change in the fingers and toes due to cold or stress), or flaking and cracking of the skin on the hands (known as 'mechanic's hands').
Myositis associated with another autoimmune disease (causing an overlap syndrome). This occurs when a patient has one of the types of myositis mentioned together with another autoimmune disease (including systemic lupus erythematosus, systemic sclerosis, vasculitis, and so on).
Polymyositis. Like IMNM, it presents as proximal muscle weakness, and these are distinguished according to the findings of the muscle biopsy.
Toxic myopathies. These are muscle diseases resulting from the use of certain substances such as alcohol, steroids, narcotics, colchicine (used to treat gout), and chloroquine (used to prevent malaria, as well as certain immune diseases such as rheumatoid arthritis and systemic lupus erythematosus).
Endocrine myopathies. These are muscular diseases caused by hormone disorders of the thyroid and parathyroid glands or the adrenal and pituitary glands.
Myopathies associated with systemic diseases.
Critical illness myopathy.
These are transmitted from parents to their children, although the patterns of inheritance vary greatly:
Muscular dystrophy. All types of this disease are degenerative, progressive, and hereditary, although there is a lot of variability between them.
Dystrophinopathies (Duchenne and Becker). These are neuromuscular diseases characterised by progressive muscle atrophy and weakness as a consequence of the degeneration of skeletal muscles, and sometimes heart muscle.
Limb-girdle muscular dystrophy. This affects the strength in shoulders and arms (scapular) and in legs and thighs (pelvic).
Steinert myotonic dystrophy. This is the most common of the dystrophies. It combines the classic pattern of all dystrophies (it is degenerative, progressive, etc.) with the so-called myotonic phenomenon, which involves difficulties relaxing a muscle once it has contracted (for example, closing the hand tightly). In addition, it is considered a more systemic disease, since very often there are cardiac, endocrine, and cataract problems, as well as early baldness, and so on.
Facioscapulohumeral dystrophy. This is characterised by progressive muscle weakness and predominantly affects the face and shoulder muscles.
Oculopharyngeal dystrophy. This affects the ocular musculature, involving the drooping of the eyelids, and the pharyngeal musculature, causing swallowing problems.
Distal myopathies. Muscle diseases with predominant weakness and atrophy that begin in the feet and/or hands, unlike most other dystrophies that affect the muscles of the arms and legs.
Muscle glycogenosis. In a broad sense this should be understood as metabolic myopathy, which, unlike other myopathies, generally implies lack of strength only when the sufferer tries to make a sustained or prolonged effort. The two most important forms are Pompe disease and McArdle disease:
Pompe disease. This can occur in its infantile form or in adult forms. It has a genetic origin and involves the deficiency of an enzyme known as alpha-glucosidase. In the infantile forms the activity of the enzyme is practically zero and, therefore, these are very serious cases (patients die before they reach one year). In the adult forms, some enzyme activity (25-30%) is retained, making them less severe. Effective treatment (enzyme replacement) has been available for almost 20 years, but this requires lifelong treatment.
McArdle disease. It is also genetic and presents as massive muscle breakdown when the patient exercises. Unlike Pompe disease, there is no effective treatment available.
Mitochondrial myopathies or encephalomyopathies. These are very rare diseases and the brain and the muscles are the most affected organs since they have higher aerobic metabolism (higher oxygen consumption).
Sergio Prieto GonzálezMedical internistDepartment of Internal Medicine
Published: 18 November 2020
Updated: 18 November 2020
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