The neuromuscular system includes motor nerve cells, peripheral nerves and muscle fibers. The motor nerve cells in the spinal cord communicate with the peripheral nerves in the arms, legs and face. The peripheral nerves in turn communicate nerve impulses to the muscles, supply sensation to the skin and send signals to the internal organs. The neuromuscular junction is where peripheral nerves communicate with muscle fibers and signal the muscles to move. Neuromuscular disorders can affect any of these components, disrupting communication pathways and resulting in various symptoms. Some neuromuscular disorders may appear as early as birth and infancy, while others usually don’t present until childhood or adulthood.
Symptoms of Neuromuscular Disorders
Symptoms, which depend on the type of neuromuscular disorder and the area of the body affected, may include muscle weakness, muscle cramps, muscle twitching and aching, muscle loss, numbness, tingling and painful sensations, balance difficulties, double vision, trouble chewing, trouble swallowing, or trouble breathing.
Lou Gehrig’s Disease: A Relatively Well-Known Neuromuscular Disorder
There are hundreds of neuromuscular disorders, some of which are extremely rare and others that are very common.
Amyotrophic lateral sclerosis (ALS), more commonly known as Lou Gehrig’s disease, is a progressive neuromuscular disorder that results from degeneration of motor nerve cells in the brain and spinal cord. About 6,000 people in the United States are diagnosed with ALS each year. The average age of diagnosis is 55, but ALS has been diagnosed in patients as early as in their 20s.
Symptoms of ALS may include muscle wasting (atrophy) and weakness, muscle twitching and cramping, difficulty with speech and swallowing, and shortness of breath.
At present there are no laboratory tests for diagnosing ALS. Instead, diagnosis relies on medical history, neurological examination, and specialized nerve conduction studies (NCS) and electromyography (EMG) tests (see sidebar). Laboratory and radiographic tests are also often performed to rule out other conditions that may mimic the symptoms of ALS.
Unfortunately, no cure for ALS currently exists, but there is one FDA-approved medication, riluzole, that has been shown to prolong life expectancy in ALS patients by a few months. Much of the treatment of ALS involves a multidisciplinary approach focused on making patients more comfortable through medications; physical, occupational and speech therapies; nutritional education; and assistive devices.
Peripheral Neuropathy: A Common Group of Disorders
One of the most common neuromuscular disorders is peripheral neuropathy, which involves dysfunction of the nerves that travel from the spinal cord to the muscles, skin and various internal organs. Peripheral neuropathy has a variety of causes, but most such patients present with similar symptoms, including abnormal sensations like burning, tingling, “pins and needles,” or numbness and weakness in the arms and legs.
Peripheral neuropathies can be inherited, but they are more frequently acquired. The most common cause of acquired neuropathy is diabetes mellitus (including Type 1, Type 2 and gestational diabetes). Other causes of acquired neuropathy include various vitamin and nutritional deficiencies, autoimmune disease, infection (such as Lyme disease), injury, exposure to toxins (including various medications), or chronic and excessive alcohol use.
Relying on a thorough clinical history and examination, diagnosis of neuropathy can be confirmed with NCS/EMG. Blood tests often can help identify the cause of neuropathy.
One very common peripheral neuropathy is carpal tunnel syndrome, which causes numbness, tingling and weakness in the hand. Diagnosis of this condition, which occurs when the median nerve in the wrist is compressed or irritated, is confirmed with an NCS/EMG test.
In most patients, carpal tunnel syndrome gets worse over time, so early diagnosis and treatment are important. With mild cases, symptoms can be relieved with noninvasive measures such as wearing wrist splints or avoiding certain activities. With more severe cases, injections or surgery may be recommended.
Treatment of other forms of peripheral neuropathy depends on the underlying cause. If neuropathy is related to diabetes, treatment typically will involve tight blood glucose management. In many cases, the cause of the neuropathy remains unknown, and treatment then focuses on symptom management.
A Neuromuscular Problem of Autoimmune Origin
Myasthenia gravis is an autoimmune disorder that affects the neuromuscular junction. Normally, when a nerve is stimulated by an electrical signal, it releases a chemical called acetylcholine (ACh). The ACh crosses the neuromuscular junction and binds to a receptor on the surface of the muscle, and this binding action “tells” that muscle to move.
With myasthenia gravis, the ACh receptors are either blocked or reduced in number and function due to abnormal immune cells, so the muscle does not receive the proper signal. As a result, the main symptom of myasthenia gravis is muscle weakness.
The hallmark pattern of this condition is muscle weakness that worsens with use and improves with rest. Weakness can manifest as difficulty swallowing, chewing or speaking clearly; drooping of the eyelids; double vision; difficulty breathing; or weakness of the arms and legs.
Diagnosis of myasthenia gravis is based on clinical history and examination, and confirmed using laboratory tests and NCS/EMG.
Treatment of myasthenia gravis includes a medication that prevents the breakdown of ACh, which in turn increases the muscle’s ability to contract. In more severe cases, additional treatment with corticosteroids and various medications that affect the immune system may be used.
Problems With Muscle Fibers
Myopathy is a general term referring to muscular weakness arising from problems with muscle fibers. Myopathies may be inherited, as in the case of muscular dystrophy, or acquired, often as a result of medication, trauma, nutritional deficiencies, infection or inflammation. In addition to weakness, symptoms of myopathy often include cramps and stiffness.
Diagnosis begins with a thorough medical history and examination to confirm the presence of weakness, which is often followed by laboratory evaluation. Measurement of a blood enzyme called creatine kinase is a good screening tool, since high enzyme levels can be an indication of muscle damage.
Treatment of myopathies varies greatly, depending on the underlying cause, often requiring the use of supportive services such as physical, occupational and swallowing therapy, as well as management of any issues involving the lungs and heart.
The Role of Neuromuscular Medicine
The prognoses for patients with neuromuscular diseases vary widely. Many individuals with neuromuscular disease live long lives, with little noticeable disability, while others have conditions that prove to be much more challenging.
Specialists in neuromuscular medicine typically work collaboratively as part of a multidisciplinary team made up of physician specialists, physical and occupational therapists, dietitians, case managers and others who can help patients manage their condition. The team monitors any progression of the disease, including any complications that may arise, and provides preventive care to help arrest or slow its progression. Treatment goals include increasing or maintaining the health and functional capability of patients, to enable them to continue to enjoy the highest quality of life possible.
Ongoing research on multiple fronts continues to deepen our understanding of neuromuscular diseases, offering hope that one day caregivers will be able to prevent and cure these conditions.
Zsofia V. Hole, MD, is on staff with Sentara RMH Neurology in Harrisonburg. Fellowship-trained in neuromuscular medicine, she joined the Sentara RMH medical staff in 2015.