23.2 Factors Affecting Neuromuscular Functioning

Blood Tests

No specific blood tests are available that diagnose disorders of the neuromuscular system with absolute certainty, however several tests are typically performed to assist with confirmation of the disorder or to rule out other causes. Nurses should understand some of the most common blood tests used to help diagnose neuromuscular disorders (Table 23.3).

Electromyography

An electromyography (EMG) is used to evaluate how muscles respond to nervous system stimulation. An EMG is performed by inserting small needles, called electrodes, through the skin until they are in the underlying muscles (Figure 23.13). After the needles are placed, the provider asks the patient to perform certain movements of the extremity (e.g., contraction, relaxation). When the muscles contract, the electrical activity in the muscles is recorded by the needle electrodes. This information is sent to a computer where the provider can review the test results in real time. This procedure takes anywhere from sixty to ninety minutes and typically does not cause the patient much pain. However, some patients do report pain with insertion of the needle and lingering soreness in the muscles for a few days after the procedure.

Figure 23.13 During an electromyography test (muscle test), a small needle is inserted into the muscle of the arm and electrical activity associated with voluntary muscle movements is recorded as waves on the monitor. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

During the test, the provider is looking for abnormal electrical activity patterns with various muscle movements. Some of the neuromuscular conditions that can be diagnosed with this type of testing include the following:

• peripheral neuropathy
• carpal tunnel syndrome
• sciatica
• pinched nerves,
• muscular dystrophy
• amyotrophic lateral sclerosis (ALS)
• myasthenia gravis

Radiographic Imaging

Several radiographic imaging tests can be used to help diagnose neuromuscular conditions. The most common are computed tomography (CT) scans and magnetic resonance imaging (MRI). The images obtained from these scans can help identify changes or abnormalities in muscle or nervous tissue that may be indicative of neuromuscular disorders. Although these tests are not usually conclusive for specific disorders, they can be used to show changes within the tissue that warrant additional follow-up and testing (Figure 23.14). Also, these scans can be used periodically after diagnosis of a neuromuscular condition to monitor the progression of the disorder over time.

Figure 23.14 An MRI scan shows injury to the muscle, indicating the need for additional diagnostic testing. (credit: Aydemir G, Cakmak S, Aydinoz S/NIH, CC BY 2.0)

Nerve Conduction Velocity Testing

A nerve conduction study, or nerve conduction velocity (NCV) testing, shows how quickly electrical signals move through nerves in the body. Two electrodes are placed on the skin over the patient’s nerves (Figure 23.15). One electrode delivers the electrical stimulus, and the other electrode records the speed of the impulse, or how quickly the electrical stimulus moves from one electrode to the other.

Figure 23.15 Two electrodes are placed on the skin over nerves as part of nerve conduction velocity testing. A very mild electrical impulse is sent through a patch or a handheld device to stimulate the nerve. (credit: Alex Durbin/Joint Base Langley-Eutis, Public Domain)

Often, this test is completed during the same visit as the EMG testing described earlier because they are performed with similar techniques and allow for more information to be obtained about the patient’s condition. The main reason that NCV testing is used is to determine whether the disorder is caused by nerve issues or muscle problems. If the NCV testing is normal, it is likely that the disorder has a muscular cause. On the other hand, if the NCV testing is abnormal (slow), the cause of the issue is more likely stemming from the nervous system. Some of the disorders that NCV testing can help diagnose include the following:

• Guillain-Barré syndrome
• carpal tunnel syndrome
• Charcot-Marie-Tooth disease
• herniated discs
• neuropathy
• sciatica

Muscle Biopsies

Muscle biopsies involve removing muscle tissue from the body for microscopic laboratory examination. The muscles used most often include the biceps or deltoids in the arms and shoulders or the quadriceps in the legs. This procedure is not used often because it is more invasive than other types of diagnostic testing, such as blood tests or imaging scans. However, it can be useful for determining specific types of muscle disorders if other tests come back inconclusive. Some examples of disorders that might be diagnosed using muscle biopsy include inflammatory myopathies (e.g., polymyositis, dermatomyositis) and specific types of muscular dystrophy.

Genetic Testing

Many neuromuscular disorders have a genetic component, meaning they can be inherited from parents. Often, when a parent or other close family member has a neuromuscular disorder, a genetic test is ordered to determine whether the disorder could have been passed on to the next generation. These tests can be performed by obtaining a swab from the cheek or a blood sample from which DNA can be analyzed. The DNA is examined for genetic mutations that are indicative of specific neuromuscular disorders. This type of test is the most accurate for diagnosing neuromuscular disorders that are genetic in nature.

Charcot-Marie-Tooth Disease (CMT)

A progressive neuromuscular disorder, Charcot-Marie-Tooth disease affects one out of every 2,500 people in the United States, and more than three million people worldwide (CMT Research Foundation, n.d.). It is caused by genetic mutations, passed down from parent to child. CMT affects the peripheral nerves, most often those of the arms, hands, legs, and feet. As the disease progresses, the patient experiences worsening numbness and muscle weakness (Figure 23.16). Other symptoms of CMT include the following:

• weak grip
• tripping or imbalance
• shuffling or dragging feet while walking
• cold hands and feet
• numbness and tingling of hands and feet
• curled toes (“hammertoes”)
• high arches in the feet

Figure 23.16 Charcot-Marie-Tooth disease causes hammertoes in addition to other possible symptoms. (credit: Liao YC, Liu YT, Tsai PC, Chang CC, Huang YH, Soong BW, Lee YC/NIH, CC BY 4.0)

Currently, there is no cure for this disease. Symptom management is attempted with pain medications, foot splints, shoe inserts, and physical and occupational therapy, but these efforts do not treat the underlying disorder.

Congenital Myopathy

A genetic muscle deformity that is present from birth is called congenital myopathy. These conditions are rare but serious because they result in lack of muscle tone and severe muscle weakness. There are several subtypes of congenital myopathy, but they all cause similar symptoms including the following:

• decreased muscle tone, known as hypotonia
• muscle weakness, particularly in the neck, shoulders, and pelvis
• breathing and feeding issues
• developmental delays, such as being unable to sit up or roll over
• falling or stumbling

Treatment for congenital myopathy typically focuses on managing symptoms and improving quality of life. This may involve physical therapy to maintain muscle strength and mobility, occupational therapy to assist with daily activities, and respiratory therapy to address breathing difficulties. In some cases, medications such as corticosteroids or medications to improve muscle function may be prescribed. Assistive devices such as braces, walkers, or wheelchairs might also be used to aid mobility. Additionally, genetic counseling may be offered to families to understand the inheritance pattern and provide information about potential risks for future generations.

Muscular Dystrophy

A group of muscular disorders called muscular dystrophy are caused by genetic mutations. All types of muscular dystrophies result in progressive muscle weakness. Nurses should be aware of some of the more common types of muscular dystrophies and their key differences (Table 23.4).

Amyotrophic Lateral Sclerosis (ALS)

Previously known as Lou Gehrig disease, amyotrophic lateral sclerosis (ALS) is a progressive neurological disorder that affects motor neurons. Onset of ALS is variable but may occur between 40 and 70 years of age. A nerve cell that receives signals from the brain and spinal cord that cause voluntary skeletal muscle movements and breathing is called a motor neuron. As ALS progresses, more motor neurons die, resulting in muscle weakness, twitching, and atrophy. Eventually, ALS causes complete loss of control over voluntary movements including walking, talking, eating, and even breathing. Some of the early symptoms of this condition include the following:

• muscle twitching, especially in the arms and legs
• muscle cramping
• spasticity of the muscles
• muscle weakness
• slurred speech
• difficulty swallowing

Other symptoms may develop later such as drooling, inability to form words and speak, unintended emotional displays (e.g., crying or laughing at inappropriate times), and severe weight loss. Unfortunately, there is no current cure for ALS; however, there are several medications available that have been shown to improve symptoms and slow the progression of the disease (e.g., riluzole [Exservan], edaravone [Radicava]). The majority of patients with ALS only survive two to five years after diagnosis (ALS Association, n.d.).

Myasthenia Gravis

An autoimmune disorder, myasthenia gravis is a disorder in which antibodies attack the neuromuscular junction (NMJ) of skeletal muscles, resulting in progressive muscle weakness (e.g., arms, hands, fingers, legs, neck) and fatigue. Initial symptoms of myasthenia gravis happen suddenly; although initial symptoms may be so mild that diagnosis is delayed. Symptoms of myasthenia gravis include the following:

• eyelid drooping, known as ptosis (Figure 23.17).
• double vision, known as diplopia
• difficulty swallowing, known as dysphagia
• difficulty changing facial expressions
• difficulty speaking
• weak neck muscles, making it difficult to support the head

Figure 23.17 Progressive muscle weakness in myasthenia gravis results in ptosis (i.e., drooping eyelids). (credit: Andrewya/Wikimedia Commons, Public Domain)

Several pharmacological therapies are available for the treatment of myasthenia gravis. These include cholinesterase inhibitors to improve communication between the nervous and musculoskeletal systems. Corticosteroids or immunosuppressants can also be used to help limit production of antibodies.

Multiple Sclerosis

A neurological disorder, multiple sclerosis (MS) causes immune system cells to attack myelin, the protective coating on nerves. MS symptoms typically begin between the ages of 20 and 40; however, the course of the disease varies from person to person. Some patients with MS may have a mild type, causing minimal symptoms. On the other hand, some patients may have a severe case that progressively worsens over time. In many cases, patients with MS have periods of exacerbation where symptoms are worse and periods of remission where symptoms improve temporarily. Nurses should understand the different subtypes of MS (Table 23.5).

The earliest signs and symptoms of MS include the following:

• blurry or double vision
• muscle weakness, most often in the hands and legs
• muscle spasms
• tingling or numbness
• clumsiness when walking
• inability to control bladder
• dizziness
• fatigue

In the later course of the disease, cognitive dysfunction is common. Patients may have trouble focusing on tasks, thinking, learning new things, or remembering memories. Unfortunately, there is no definitive cure for MS at present. There are, however, many treatments available for symptom control. Specifically, corticosteroids are used in an attempt to prevent the body from attacking its own myelin cells. Several disease-modifying medications have been approved for treatment of MS that work similarly to steroids to suppress the immune system.

Cerebral Palsy

An umbrella term for a group of disorders that affect the ability to move and stay balanced is cerebral palsy (CP), which occurs because of damage to the brain during pregnancy, childbirth, or in early infancy. There are several subtypes, each with their own associated signs and symptoms. Some early signs that a baby may have one of the forms of CP include the following:

• head lag when being picked up from lying on the back
• overly stiff or floppy extremities
• overextension of back and neck, making it seem as if the baby is pushing themselves away from the caregiver when being held
• leg stiffening or scissoring when being picked up
• inability to roll over after 6 months of age
• lopsided crawling or inability to crawl at all

Currently, there is no cure for CP; however, several interventions are available to treat symptoms of the condition. These interventions include medications, braces and adaptive devices, physical and occupational therapies, and potentially surgery in severe cases.

Spinal Cord Injuries

When there is damage to the spinal cord, a spinal cord injury occurs, often as a result of trauma (e.g., a motor vehicle accident, a fall) or cancer. The rest of the body below the damaged level of the spinal cord is affected and often results in irreversible damage and limited mobility. In some cases, the damage to the spinal cord is incomplete, leaving some sensation and mobility below the level of damage. However, in complete spinal cord injury, all feeling and ability to control movement are lost. This complete loss of sensation and mobility is called paralysis. Paralysis can be further classified as tetraplegia (quadriplegia), which is paralysis from the neck down, or paraplegia, which is paralysis of the legs and portions of the trunk but not the arms. Common symptoms of spinal cord injuries include the following:

• immobility of affected extremities
• loss or changes in sensation (e.g., feeling extreme temperatures)
• loss of bowel or bladder control
• involuntary muscle spasms
• hyperactive reflexes
• sexual dysfunction
• trouble breathing (more common with higher spinal cord injuries)

Treatment for spinal cord injuries depends on the extent of the damage but typically involves intense physical and occupational therapy.

Loss of Balance

Loss of balance in neuromuscular conditions occurs via two main mechanisms. First, neuromuscular disorders cause muscle weakness, which in turn makes it difficult to maintain balance and posture. When muscles of the trunk and core are weak, the center of gravity of the body is off, making it difficult to stay balanced. The other mechanism behind loss of balance is related to slow nerve signals being sent to the muscles, such as seen in multiple sclerosis. Essentially, the muscles are not receiving signals from the brain in a timely manner, making it difficult to move in a way that consciously or unconsciously maintains balance and posture. Loss of balance can be dangerous, especially in older adults, who are already more prone to falls. For neuromuscular conditions that cause a loss of balance, adaptive devices may be required to assist with ambulation and other movements to decrease the risk of a fall and subsequent injury.

Muscle Weakness and Stiffness

Muscle weakness and/or stiffness are hallmark symptoms of many neuromuscular conditions. In fact, they are often the presenting symptom that indicates the need for follow-up, which leads to eventual diagnosis of the disorder. In some conditions, such as with myasthenia gravis, muscle weakness is related to the direct muscle damage that occurs as part of an autoimmune system attack on muscle tissue. In many other neuromuscular conditions, brain or nerve damage results in slowing of nerve signals sent to muscles. With a lack of nerve signals being sent to skeletal muscles, they are not used as often or as efficiently, resulting in weakness related to immobility. Most neuromuscular conditions that cause muscle weakness require extensive physical and occupational therapy in conjunction with adaptive devices to preserve and improve the patient’s mobility.

Muscle Atrophy

Wasting and breakdown of muscle tissue, muscle atrophy, is another common clinical manifestation of many neuromuscular disorders (Figure 23.18). When muscles are not being used often enough, they become weak and waste away. This wasting away of muscles further contributes to the cycle of muscle weakness, resulting in an inability to effectively move and maintain balance and posture.

Figure 23.18 Muscle atrophy occurs as a manifestation of many neuromuscular conditions. (credit: “Case of progressive muscular atrophy”/Wellcome Images, CC BY 4.0)

Pain

Chronic pain is a common clinical manifestation of many neuromuscular conditions. In some conditions, such as Charcot-Marie-Tooth disease, pain can be severe and debilitating, affecting all aspects of everyday life. Other conditions, such as mild forms of multiple sclerosis, may cause some pain but not enough to significantly affect activities of daily living (ADLs). As with all patients, it is important for the healthcare team to recognize that “pain is what the patient says it is,” and treat them accordingly. It is also important to know that patients with neuromuscular disorders often have good days where pain is minimal and bad days where pain is debilitating. Pain management should be an included component in the care plan for every patient who is diagnosed with a neuromuscular disorder.

Breathing Impairment

Breathing impairment may occur with some neuromuscular disorders, most often at the end of the course of the disease. In conditions that cause muscle weakness and atrophy, muscles such as the diaphragm and intercostal muscles are eventually affected, resulting in an inability to breathe effectively. In fact, respiratory muscle weakness is one of the leading causes of death in patients with neuromuscular disorders (Khanbabaee et al., 2023). Additionally, in conditions that affect the cervical spinal cord, such as with high spinal cord injury, the nerves that innervate the breathing center of the brain may be affected, which inhibits the patient’s ability to breathe. These patients often require a tracheostomy (an opening in the trachea into which a tube is placed that allows for mechanical ventilation to be delivered) for the course of their life because they are no longer able to breathe or breathe adequately on their own.

Swallowing Impairment

Difficulty swallowing, or dysphagia, is a common clinical manifestation of many neuromuscular disorders. Muscles of the mouth, pharynx, and upper esophagus become weakened, making it difficult for the patient to chew and swallow effectively. This is a concern for many reasons. First and foremost, dysphagia increases the risk of aspiration, which occurs when food or other foreign particles enter the airway. Aspiration can become life-threatening when it limits the patient’s ability to breathe effectively. Another concern with dysphagia is that it can significantly and adversely affect the patient’s quality of life. Dysphagia can cause malnutrition and can also take the enjoyment out of eating, resulting in depression and negative feelings toward food.

Vision Impairment

Vision impairment is not quite as common as the symptoms discussed in the previous sections but can still occur as a clinical manifestation of some neuromuscular disorders. In most cases, there is damage to the optic nerve, which results in pain and decreased vision. This is especially true for conditions such as multiple sclerosis that cause demyelination of nerve cells. When the optic nerve is attacked, vision is negatively affected.