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Nerve Disease ALS and Gradual Loss of Muscle Function
Mary E. Miller
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eBook - ePub
Nerve Disease ALS and Gradual Loss of Muscle Function
Mary E. Miller
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About This Book
Amyotrophic lateral sclerosis, ALS, is a common form of motor neuron disease that involves a loss of function in upper and lower motor neurons. ALS causes a progressive loss of muscle function that frequently initiates in the limbs, called limb-onset ALS, or initiates in facial muscles, called bulbar-onset ALS. This book describes the current understanding of ALS symptoms, diagnosis, causes, and treatments. Initial symptoms vary in type of muscle dysfunction, intensity of symptoms, and speed of disease progression. Diagnosis requires loss of function in both upper and lower motor neurons for limb- and bulbar-onset ALS, distinguishing ALS from other neuromuscular diseases. Although no cause or initial trigger has been determined for ALS, eventually both limb and bulbar muscles will show dysfunction as the disease progresses. In later stages of the disease, muscle dysfunction typically leads to respiratory failure and death. Management of neurotransmitter levels in patients can prolong life by months, but no cure exits for the disease. Other treatments exist that can help patients manage muscle weakness or spasms as the disease progresses. The book concludes by considering future detection, treatment, and diagnostic approaches with the goal of preventing disease initiation or progression.
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CHAPTER 1
Symptoms and Diagnosis
The initial symptoms of muscle weakness and spasm associated with amyotrophic lateral sclerosis (ALS) may be overlooked because they can vary from patient to patient and initially be subtle. As time progresses, subtle symptoms will develop into more obvious symptoms. Symptoms can occur in any muscle group, though initial symptoms are frequently associated with limb or bulbar muscles. ALS symptoms can include spasticity (stiffness), increased reflexes, weakness of muscles, muscle atrophy or wasting, or fasciculation (twitching). Loss of upper motor neuron function is associated with symptoms of muscle stiffness, spasm, slow movement, and overactive reflex responses and eventually the loss of control of voluntary muscles. Lower motor neuron loss causes symptoms more associated with loss of muscle function, muscle weakness, muscle wasting and twitching. Typically, when symptoms progress more slowly early in the disease, they will continue to progress more slowly at later disease stages. Likewise, when symptoms progress more quickly early in disease progression, they will continue to progress more quickly in later stages. ALS rarely interferes with the patient’s personality or ability to think, though some studies suggest that cognitive loss may occur at later stages of disease progression. Approximately 50 percent of ALS patients develop pseudobulbar emotional lability independent of other symptoms. In this case, the patient will cry, laugh, or yawn without control leading the patient to a sense of a loss of mental control. These symptoms do not correlate with cognitive decline and do not necessarily indicate a mood disorder, but can be socially difficult and very disturbing for the patient. Depression as a consequence of decreased body function is frequent in ALS patient and caregivers. There is no cure for ALS, and once diagnosed, expectations are that the patient will die from respiratory failure, as occurs in 80 to 90 percent of the cases. Other causes of death from ALS include heart failure (10 percent); pneumonia and suicide at a much lower frequencies.
The early signs of ALS vary among patients because different motor neurons lose function and loss of those motor neurons would affect muscle function in different parts of the body. Historically, ALS has been described based on the region of the body where symptoms are first noticed. When symptoms start in a limb, it is described as limb-onset ALS, if it begins with speech (dysarthia) or swallowing (dysphagia) problems, it is called bulbar-onset ALS. Bulbar-onset ALS is named for the location of the motor neurons that are involved, specifically the corticobulbar region of the brain stem. Both limb-onset and bulbar-onset ALS involve the loss of upper and lower motor neuron functions. Limb-onset ALS can begin in the lower limbs or upper limbs and can involve one limb with progression to the other or initiate simultaneously in both limbs. While the average life expectancy after diagnosis for ALS patients ranges between 2 and 5 years, approximately 5 percent of patients survive for more than 10 years and that population usually has limb-onset ALS. Slower rates of disease progression are also associated with rare forms of limb-onset ALS where progressive wasting and weakness of one or more limbs occur with delayed progression to other parts of the body. Bulbar-onset ALS progresses more quickly than limb-onset ALS and occurs in approximately 25 to 30 percent of all ALS cases.
Limb-onset ALS symptoms initially present as the patient having difficulty carrying out manual tasks that require coordination between the legs and/or arms. For example, the patient might experience tripping or gait changes due to motor neuron dysfunction in the legs. Motor neuron dysfunction in the arms might result in a reduction in fine motor skills so that buttoning clothes or writing become noticeably difficult. Symptoms can also include difficulty in raising arms or moving the entire body to climb stairs or to get out of chairs. Over time, fasciculation (twitches) might develop in addition to slowness in movement and reduced dexterity. Patients with symptoms of limb-onset ALS will eventually develop bulbar ALS symptoms in later stages of the disease. Speech may be affected along with spasms of the jaw, face, voice box, throat, and tongue. Specific symptoms associated with bulbar-onset ALS that affect speech include poor articulation, strained voice, breathy speech pattern, and a decrease in the range of pitch or loudness of the voice. At times, vocal cord spasms can create the feeling that air is not being moved in and out of the lungs. Eye muscles are not usually involved, and so dysfunction of the eyes is not strongly associated with ALS. Approximately 93 percent of patients with bulbar-onset ALS lose speech, 86 percent have difficulty swallowing, 64 percent show tongue twitching, and 19 percent experience vocal cord spasms. In both limb- and bulbar-onset ALS, as the disease progresses, patients will lose voluntary muscle control, which will impact the ability of the patient to move, and so they may need mechanical assistance in doing so. Patients may become unable to communicate verbally. Eventually, patients experience difficulty breathing and may need noninvasive or invasive breathing assistance. Most ALS patients succumb to the disease because of respiratory failure.
Diagnosing ALS
Given that ALS symptoms can vary among patients and exhibit subtle onset, initial diagnosis focuses on ruling out other possible causes for the symptoms presenting in the patient. Even in the case of symptoms involving both upper and lower motor neurons, other diseases are ruled out before the diagnosis of ALS. In order to establish that the upper and lower motor neurons are functioning properly, specific tests are given to measure neuron function. In the case of lower motor neurons, one common test is the electromyography or EMG. During EMG, a device measures neuronal movement of electrical signal during a voluntary muscle contraction to detect changes in the electrical signals in the muscle. Nerve conduction studies (NCS) are frequently performed in conjunction with the EMG to assess speed and intensity of nerve impulses. In this case, the stimulation to the nerve is applied to the surface of the skin through small electrodes to stimulate the muscle, and successful muscle stimulation is measured by additional electrodes. Certain EMG and NCS test result patterns are consistent with ALS, but other patterns might support the diagnosis of different diseases such as peripheral neuropathy. Blood and urine tests would likely be used to rule out other possible causes of the patient’s symptoms. For example, the presence of high levels of creatine kinase in the blood system is more consistent with muscular dystrophies than with ALS. There are also many infectious diseases that can give rise to symptoms associated with ALS. HIV infection, polio, Lyme disease, and West Nile virus are examples of infectious agents that might need to be ruled out before diagnosing a patient with ALS.
ALS is characterized by defects in both upper and lower motor neurons, so tests to measure upper motor neuron function are also used. Magnetic resonance imaging (MRI) scans can provide insight into brain structures. The MRI captures a detailed series of images that show cross-sections through the brain. Briefly, MRI uses a very strong magnet to align the polarity (a type of directionality) of the hydrogens (protons) present in our body (largely found in water). A radio wave is passed through the patient to make the protons change direction. Once the radio wave is removed, the protons move bac...