Medical professionals use the term “muscle disorders” to refer to a wide range of conditions that primarily affect the skeletal muscles and are often accompanied by progressive muscle weakness. In medical terminology, such a condition is referred to as myopathy. The cause may lie directly within the muscle tissue or result from a disruption in the transmission of signals from the nerve cell to the muscle, which is then termed a neuromuscular disorder. The spectrum ranges from genetically caused muscular dystrophy, which often begins in childhood, to acquired myositis, an inflammatory condition that occurs in adulthood. Metabolic disorders or autoimmune diseases can also damage muscle tissue. Since symptoms such as muscle wasting or rapid fatigue occur in many neurological conditions—such as amyotrophic lateral sclerosis or spinal muscular atrophy—precise diagnosis in neurology is crucial for treatment.
What is myopathy?
Myopathy is the medical term for muscle disorders. “Myo” stands for muscle and “pathy” for disease. The skeletal muscles are most commonly affected; the heart is affected less frequently (medically known as cardiomyopathy). Myopathy is an umbrella term for all disorders that affect the muscles.
Since there are many different causes of muscle disorders and muscles account for a large portion of the human body’s mass, the various causes and characteristics of muscle disorders will be discussed in more detail below.
What types of myopathies are there, and what are their causes?
There are a wide variety of different muscle disorders; they can be broadly classified into
- congenital and
- acquired forms.
Congenital forms are inherited, meaning they are present at birth (or in the womb). For this reason, they are also referred to as primary forms (primary = first, initial). They often cause problems at birth, but in some cases symptoms do not become apparent until later. Males are affected by inherited muscle diseases far more frequently, which is due to the pattern of inheritance. Boys have one Y chromosome and one X chromosome, while girls have two X chromosomes. Since a healthy X chromosome protects against the disease, both genes (the one from the mother and the one from the father) must be defective in girls, whereas in boys, only one needs to be defective.
Acquired myopathies develop later in life due to external factors (such as taking certain medications) or other diseases (including rheumatic diseases). They are therefore also called secondary myopathies (secondary = occurring second, subsequently). Rheumatism is often associated with joint pain; it is also referred to as “rheumatoid arthritis.” However, it can also affect the muscles.
What exactly happens to the muscles in myopathy?
Myopathy causes a disturbance in muscle function or muscle development.
Broadly speaking, these functional disorders can be divided into:
- Decrease in muscle mass (muscular dystrophy)
- Impaired muscle relaxation (myotonic syndromes)
- Impaired energy supply (mitochondrial myopathy)
Which form of myopathy is the most common?
The most common form of myopathy is muscular dystrophy (muscle wasting). This typically involves a reduction in muscle mass, which can be attributed to various causes. Here, too, a distinction is made between
- primary and
- secondary muscular dystrophies.
Primary means that the cause lies within the muscle itself. These are usually hereditary diseases, which are very rare.
Secondary forms of muscular dystrophy stem from other diseases or pathological conditions, not from the muscle itself. They are not classified as a disease in their own right, but rather as a symptom of another underlying condition.
Causes of secondary myopathies include, among others:
- Cushing’s disease
- Hypothyroidism
- Vitamin D deficiency
- Selenium deficiency
- Lipid storage disorders
Myopathy can also be caused exogenously by:
- Toxins
- Alcohol
- Medications such as statins or cortisone
Are there several types of primary muscular dystrophy?
Depending on the pattern of inheritance and the muscles affected, congenital muscle wasting diseases can differ significantly from one another in terms of their clinical presentation and symptoms. They are often named after the researchers who first described them, but they are all characterized by progressive muscle wasting.
The most common forms of primary muscular dystrophy are Duchenne muscular dystrophy and Becker-Kiener muscular dystrophy. Limb-girdle muscular dystrophies and Emery-Dreifuss muscular dystrophy type 1 are also classified as muscular dystrophies.
What causes secondary muscular dystrophies?
In secondary muscular dystrophies, the muscles themselves are healthy; the loss of muscle mass is caused by other conditions. For example, malnutrition with protein deficiency, tumors, or vitamin deficiency can lead to the loss of muscle mass.
However, immobility—that is, a restriction or loss of mobility—often leads to a loss of muscle mass due to a lack of physical activity. Examples include severe bone and joint injuries that prevent a person from getting out of bed. Furthermore, a herniated disc can also lead to muscle paralysis and a loss of muscle mass.
Rarely, but also as a cause of secondary muscle atrophy, an induced coma can be a factor. The longer the coma lasts, the greater the muscle atrophy and the longer it takes to rebuild muscle mass afterward.
What is myotonic myopathy?
A characteristic feature of myotonic muscle disorders is prolonged muscle tension. As a result, the muscle cannot relax properly, leading to cramping. To explain the term: “tonus” is the technical term for tension or contraction, and “myo” stands for muscle. This form of muscle disorder, which is prone to cramps, is therefore also referred to as myotonic myopathy.
However, since it is not only the muscles that are affected, but also many other organs and organ systems (e.g., the eyes, heart, brain, and psyche), the term “myotonic syndromes” is used. In medicine, complex diseases with many different clinical presentations and symptoms are often referred to as syndromes.
In most cases, myotonic syndromes are congenital muscle disorders; however, acquired myotonias also exist, including those associated with neurological disorders, medications and their side effects, drug and alcohol abuse, or kidney disease.
What characterizes mitochondrial myopathies?
Mitochondrial myopathies are caused by a disturbance in the energy metabolism of certain cellular components known as mitochondria. Mitochondria are the powerhouses of the cells; this is where all energy metabolism takes place. Since skeletal muscle makes up the largest portion of the body’s musculature and is where most movement and exertion occur, symptoms of mitochondrial myopathies almost without exception affect the skeletal muscles.
However, muscles in other organs and organ systems can also be affected, which is why a wide variety of symptoms and problems can arise in these areas as well. For example, the nervous system, the eye, and the inner ear may also be affected. Disorders of the gastrointestinal tract, the liver, or the pancreas also occur. Mitochondrial diseases are often referred to as multisystem diseases, as they affect many different organs.
What are the symptoms of myopathy?
The main symptom of myopathy is muscle weakness. The severity of this weakness depends primarily on the cause of the myopathy. Mild forms of myopathy, for example, manifest only as weakness during or after physical exertion. Consequently, limitations are rarely observed in daily life, if at all, except during athletic activities or heavy physical labor.
However, there are also severe forms of myopathy, such as Duchenne muscular dystrophy. In the early stages, this muscle weakness is initially noticeable only through frequent stumbling or falling. As early as ages 5 to 7, affected children can no longer stand up from a sitting position without assistance. By age 12, most patients with Duchenne muscular dystrophy are confined to a wheelchair, and by the time they reach adulthood, they generally require full-time care.
How are muscle disorders diagnosed?
If myopathy is suspected, a detailed family history should be taken first. Due to the mode of inheritance described above, mothers in particular may be undiagnosed—that is, healthy—carriers of the defective gene.
Laboratory diagnostics provide further clues to possible causes. For example, blood tests can reveal nutrient deficiencies or be used for genetic testing.
Before genetic analysis is performed, an electromyography (EMG) is usually conducted first. This is a neurological diagnostic procedure that measures electrical muscle activity. It can thus detect muscle weakness. In addition, an EMG can help determine whether the cause of the muscle weakness lies in the muscles themselves or in the nervous tissue.
Imaging techniques such as computed tomography (CT) or magnetic resonance imaging (MRI) visualize the affected muscle areas and can highlight abnormalities.
A muscle biopsy, in which the doctor removes a tissue sample from the muscle and then sends it to the laboratory for histological examination, serves to further confirm the diagnosis with precision. However, it is performed only when there is sufficient suspicion of a primary myopathy, as it is a sometimes painful diagnostic procedure that carries a risk of complications (bleeding, post-procedural bleeding, and muscle and nerve injury).
How are muscle disorders treated?
Treatment options for myopathy are varied and depend on the underlying cause. In cases of secondary myopathy, the underlying condition is treated first, which in most cases also alleviates the muscle weakness. For example, patients with hypothyroidism are prescribed thyroid hormones, and in cases of vitamin or mineral deficiency, supplementation with the appropriate nutrient provides relief.
In primary myopathies, however, causal treatment is not possible. The goal of therapeutic measures is to minimize the consequences of muscle weakness for as long as possible.
Physical therapy and medication can alleviate symptoms and help maintain muscle strength. Occupational therapy, on the other hand, helps patients cope with daily life. In addition, those affected benefit from appropriate assistive devices such as a cane, a walker, or a wheelchair.
If the muscle weakness affects not only the skeletal muscles but also the heart muscle, medication may be helpful. Patients are then prescribed medications to strengthen the heart muscle and treat cardiac arrhythmias. In some cases, the implantation of a pacemaker may also be necessary as part of treatment.
Myopathies are thus a group of muscle disorders with a wide variety of causes. The symptoms and treatments for these muscle disorders are just as varied as their causes.
FAQ: The 8 Most Important Questions About Muscle Disorders and Myopathies
What is the difference between a myopathy and a neuromuscular disorder?
A “pure” myopathy refers to a disorder in which the problem lies primarily in the muscle cells or muscle fibers themselves, as is the case with muscular dystrophy or a metabolic myopathy. A neuromuscular disorder, on the other hand, is a broader term that also includes conditions in which the nervous supply to the muscles is affected. This means that the damage can occur in the nerve cells of the spinal cord, in the peripheral nerve fibers, or at the point of transmission to the muscle—the motor end plate. Examples include amyotrophic lateral sclerosis and spinal muscular atrophies, which lead to muscle wasting even though the muscle was initially intact.
What symptoms indicate a muscle disorder?
The primary symptom of almost all myopathies is painless muscle weakness, which often develops gradually. Those affected notice that they have difficulty climbing stairs, cannot hold their arms up while combing their hair, or tire quickly. Another symptom is visible muscle wasting—known technically as muscle atrophy—in which muscle mass decreases. In some forms, muscle pain, cramps, or myotonia—a condition in which the muscle cannot relax immediately after contraction—may also occur. If the respiratory muscles or the heart muscle are affected, shortness of breath and heart problems may also develop.
What is Duchenne muscular dystrophy?
Duchenne muscular dystrophy is the most common form of genetically caused muscle disease in childhood and affects almost exclusively boys. Due to a genetic defect, the protein dystrophin is missing, causing muscle cells to become unstable and die. The disease begins in early childhood with weakness of the pelvic girdle muscles, leading to a waddling gait. The disease is progressive, so that most patients become wheelchair-bound by adolescence as muscle degeneration advances inexorably.
How is myopathy diagnosed?
The diagnostic process usually begins with a neurologist, who takes a thorough family history and examines muscle strength and reflexes. An important diagnostic tool is the EMG (electromyography), which measures electrical activity in the muscle to distinguish between nerve and muscle damage. Blood tests often reveal elevated levels of muscle enzymes such as creatine kinase (CK), which indicate the breakdown of muscle fibers. To determine precisely whether the condition is inflammation (myositis), a mitochondrial defect, or a dystrophy, a muscle biopsy or genetic analysis is often necessary.
What are mitochondrial myopathies?
Mitochondrial myopathies are a group of metabolic disorders in which the mitochondria—the cells’ powerhouses—do not function properly. Since muscles require a great deal of energy, they are particularly sensitive to this defect. Symptoms often include extreme exercise intolerance, severe muscle pain after exercise, and general weakness. Since mitochondria are present in all cells, other organs such as the brain or the eyes are often affected as well, which makes this form of the disease very complex.
Can a muscle disorder be cured?
Whether a cure is possible depends heavily on whether the disease is genetic or acquired. Acquired, inflammation-related myositis can often be effectively treated with medication such as cortisone or immunosuppressants, allowing muscle strength to recover. For genetic forms such as muscular dystrophies, a cure that addresses the underlying cause is generally not yet possible; however, there are new gene-based treatment options that can slow the progression of the disease. In these cases, physical therapy and occupational therapy are key to maintaining mobility for as long as possible and preventing contractures.
What is sarcopenia?
Sarcopenia refers to the age-related loss of muscle mass and muscle strength, also known as age-related muscle wasting. Although it is a physiological process, it can become a medical condition if muscle weakness leads to falls and a loss of independence. Sarcopenia must be distinguished from pathological myopathy, as it is primarily caused by the aging process, lack of physical activity, and hormonal changes, but can be positively influenced by exercise and nutrition.
What role does genetics play in muscle disorders?
Genetics plays a central role, as many myopathies are directly caused by mutations in genes that are important for the structure or function of muscle cells. These congenital or inherited muscle disorders are often passed down through families, which is why family history is important. Modern genetic tests can now identify many of these defects, which is crucial for prognosis and counseling regarding plans to have children.
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About the medical author
Prof. Dr. med. Susanne Regus
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Prof. Dr. med. Susanne Regus – medical author: expert articles, professional insights and medical expertise in the Leading Medicine Guide.
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