A neuromuscular disease (NMD) is a disorder that affects the peripheral nervous system.
The principle effect of neuromuscular disorders is therefore on the ability to perform voluntary movements. Neuromuscular disorders can be categorized as:
- Muscular dystrophies – involving the structure of the muscle cells. Eg. Duchenne Muscular Dystrophy, Becker,….
- Peripheral motor neuron diseases – involving muscle-controlling nerve cells of the arms, legs, neck and face. Eg. Charcot-Marie tooth disease, Friedreich’s ataxia…
- Motor neuron diseases – involving nerve cells in the spinal cord. Eg. Spinal Muscular Atrophy, ALS…
- Neuromuscular junction diseases – involving the site where nerves and muscles meet. Eg. Myasthenia gravis, Lambert-Eaton syndrome…
- Myopathies – involving tone and contraction of muscles controlling voluntary movements; may include inflammation of muscles or related tissues. Eg. Dermatomyositis, Hyperthyroid myopathy…
- Metabolic diseases of the muscle – involving errors in metabolism in producing energy in muscle cells. Eg. Mitochondrial myopathy, acid maltase deficiency…
Patients with neuromuscular diseases can have weakness, loss of muscle bulk, muscle twitching, cramping, numbness, tingling, and a host of other symptoms. Problems with the nerve-muscle junction can also cause droopy eyelids, double vision, and weakness that worsen with activity. Some NMDs can also cause difficulty with swallowing and sometimes with breathing. NMDs cause significant incapacity, including, at the most extreme, almost complete paralysis.
Incidence rates for most NMDs range from 0.05 to 9 per 100,000/yr. Most NMDs show prevalence rates between 1 and 10 per 100,000 population.
Neuromuscular disorders progress over time. Most NMDs onset is at birth, some manifest in childhood and others have adult onset. The disease may be genetically passed down, caused by autoimmune disorders or due to a spontaneous genetic mutation, inflammation, exposure to environmental chemicals and poisoning or tumors. Some NMDs simply have no known cause.
Diagnosing a neuromuscular disorder is a multistep process starting with direct clinical observation which can identify atrophy or loss of muscle bulk and/or tone may lead a physician to order other diagnostic tests, including:
- Blood test to check for elevated enzymes
- Magnetic resonance imaging (MRI) scan of the brain and spinal cord
- Lumbar puncture (spinal tap) to check cerebrospinal fluid
- Electromyography (EMG) to record the electrical activity of each muscle
- Nerve conduction studies to see how well signals travel from nerve to muscle
- Muscle biopsy to examine a sample of muscle tissue under a microscope
- Genetic testing to confirm gene mutations
There is no cure for most NMDs, but they can be effectively managed and treated. Interventions include:
- Drug therapy – Some forms of nerve and muscle disease can be treated effectively with medications which include immunosuppressive drugs. Anticonvulsants or antidepressants may be used to treat neuropathic pain.
- Referrals to appropriate specialists – Patients may receive referrals to surgeons for neurological surgery, thoracic surgery, orthopedic surgery or other types of surgery. They may also be referred to physical, occupational, speech or rehabilitation specialists; physiatrists; pulmonary medicine specialists; or ophthalmologists.
- Patient and family education and counselling.
There are currently a number of pharmaceutical companies working on identifying treatments for some of these NMDs. This has raised hopes amongst patients and their families and the patients advocacy groups are playing a significant role in supporting disease awareness initiatives and funding for research.
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