Neuromuscular disease is a broad term that scientists use to refer to a variety of diseases and disorders that affect parts of the neuromuscular system, which includes the muscles, the peripheral motor nerves, the neuromuscular junction (where muscles and nerves meet), and motor neurons in the spinal cord. All of these diseases and disorders are progressive, leading to muscle breakdown and increased weakness, which contribute to certain physical symptoms, such as impairment of fine motor skills and speech. Patient life span varies by condition. Although many neuromuscular diseases and disorders primarily affect voluntary muscles, they also may lead to respiratory and cardiovascular problems.
Some neuromuscular diseases and disorders are genetic, while others are spontaneous and have no known cause. Neuromuscular diseases and disorders can present during any stage of life, from birth to adulthood. Most neuromuscular diseases and disorders have no known cure. However, certain treatments have helped improve life expectancy and quality of life in some patients.
Types of Neuromuscular Diseases and Disorders
Scientists group neuromuscular diseases and disorders into six categories: muscular dystrophies, peripheral motor neuron diseases, motor neuron diseases, neuromuscular junction diseases, myopathies, and metabolic diseases of muscle. A few examples of the diseases and disorders in each category follow.
Muscular dystrophies (MD)—these diseases and disorders are related to issues involving the structure of muscle cells.
Duchenne muscular dystrophy is the most common dystrophy among children. The disorder usually presents between ages two and six. It leads to muscle wasting and overall weakness. Duchenne MD primarily affects boys but also may affect girls.
Myotonic muscular dystrophy, also known as Steinert's disease, affects a patient’s ability to relax the muscles. This disease progresses slowly, and it often affects the face, hands, and feet first. The disease can present in childhood or adulthood.- Peripheral motor neuron diseases—nerve cells that control the muscles of the arms, legs, neck, and face are affected in these diseases.
Charcot-Marie-Tooth disease is characterized by weakness in and wasting of the muscles and nerves in the hands, arms, and legs. In some cases, patients also may suffer from impaired vision and hearing.- Friedreich's ataxia is a rare inherited condition in which patients suffer from shakiness and a lack of coordination along with muscle weakness. Heart problems and issues with speech also may occur. The onset of Friedreich's ataxia occurs later in childhood, often between ages seven and thirteen.
Motor neuron diseases—these diseases affect the spinal cord’s nerve cells.
Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, is a progressive degenerative disease that affects the nerve cells in the brain and spinal cord. The disease, which affects more men than women, usually presents between the ages of forty and sixty. At first, patients often have difficulty walking and writing and may exhibit speech problems. Later, patients lose the ability to move and become paralyzed.- Spinal-bulbar muscular atrophy only affects males. It can present at any time between adolescence and old age. This disease affects the limbs as well as the tongue and other muscles necessary for speaking and eating (chewing and swallowing).
- Neuromuscular junction diseases—these diseases involve issues with the transmission of signals from nerves to muscles.
- Congenital myasthenic syndromes are a category of diseases and disorders characterized by overall weakness and muscle fatigue that becomes worse with physical activity. All muscles used for movement may be impaired, but the muscles involved in eating and breathing are most commonly affected. These diseases may present at any time.
- Myopathies—these diseases affect tone and contraction of voluntary muscles.
- Central core disease usually presents at birth or shortly thereafter. This disease delays the development of motor skills and can lead to issues with the hip.
Dermatomyositis is a disease characterized by a bluish skin rash and progressive weakness in the limbs and neck. The disease, which may present at any time from childhood to age sixty, may be controlled by diet and certain drugs.- Metabolic diseases of muscle—these diseases result from metabolic problems in the production of energy in muscle cells.
- Mitochondrial myopathy presents at any time between early childhood and early adulthood. It is characterized by severe muscle weakness and also may involve problems with the brain that could lead to seizures, deafness, and cognition issues in some patients.
Treatment of Neuromuscular Diseases and Disorders
Most neuromuscular diseases and disorders have no known cure. However, some treatment options can help increase patient life span and improve quality of life.
Special equipment—such as wheelchairs, braces, and walkers—can help patients with mobility issues, and certain technologies, such as computers, enable patients with speech impairments to communicate. Physical or occupational therapy may help some patients maintain mobility and ward off certain side effects of their diseases. Few drugs are approved to treat neuromuscular diseases, but some have proven effective. One such drug is the steroid prednisone, which has been shown to improve muscle strength and delay the loss of function in the muscles of patients with Duchenne MD. Respiratory and cardiac treatment also may help improve life expectancy in some patients.
Scientists continue to explore new ways to fight neuromuscular diseases. Some studies have focused on
stem cells
, cells in the early stages of development that have the potential to form different types of cells. Scientists think that muscle stem cells could be used to fix or replace deteriorating muscle fibers. Other treatments in development involve the use of small-molecule drugs, which are smaller than cells, to target specific parts of the body with fewer side effects. Scientists also are investigating protein therapies, which could replace deficient or missing proteins that contribute to certain diseases.
Bibliography
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