Amyotrophic lateral sclerosis

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Amyotrophic lateral sclerosis
Synonyms Lou Gehrig's disease, Charcot's disease,[1] motor neurone disease (MND)
ALS Coronal.jpg
An MRI with increased signal in the posterior part of the internal capsule which can be tracked to the motor cortex, consistent with the diagnosis of ALS
Specialty Neurology
Symptoms Stiff muscles, muscle twitching, gradually worsening weakness[2]
Complications Difficulty in speaking, swallowing, breathing[2][3]
Usual onset 50s–60s[4]
Causes Unknown (most), inherited (few)[4][5]
Diagnostic method Based on symptoms[5]
Treatment Non-invasive ventilation[6]
Medication Riluzole, edaravone[7][8]
Prognosis Life expectancy 2–4 years[9]
Frequency ~2.5 per 100,000 per year[4][10]

Amyotrophic lateral sclerosis (ALS), also known as motor neurone disease (MND), or Lou Gehrig's disease, is a specific disease which causes the death of neurons controlling voluntary muscles.[3][5][11] Some also use the term motor neuron disease for a group of conditions of which ALS is the most common.[2] ALS is characterized by stiff muscles, muscle twitching, and gradually worsening weakness due to muscles decreasing in size.[2] This results in difficulty speaking, swallowing, and eventually breathing.[2][3]

The cause is not known in 90% to 95% of cases.[5] The remaining 5–10% of cases are inherited from a person's parents.[4] About half of these genetic cases are due to one of two specific genes.[5] The underlying mechanism involves damage to both upper and lower motor neurons.[2] The diagnosis is based on a person's signs and symptoms, with testing done to rule out other potential causes.[5]

No cure for ALS is known.[5] A medication called riluzole may extend life by about two to three months.[7] Non-invasive ventilation may result in both improved quality and length of life.[6] The disease can affect people of any age, but usually starts around the age of 60 and in inherited cases around the age of 50.[4] The average survival from onset to death is two to four years.[9] About 10% survive longer than 10 years.[5] Most die from respiratory failure.[4] In much of the world, rates of ALS are unknown.[4] In Europe and the United States the disease affects about two to three people per 100,000 per year.[4][10][12]

Descriptions of the disease date back to at least 1824 by Charles Bell.[13] In 1869, the connection between the symptoms and the underlying neurological problems was first described by Jean-Martin Charcot, who in 1874 began using the term amyotrophic lateral sclerosis.[13] It became well known in the United States in the 20th century when in 1939 it affected the baseball player Lou Gehrig and later worldwide following the 1963 diagnosis of cosmologist Stephen Hawking.[14][15] In 2014, videos of the Ice Bucket Challenge went viral on the Internet and increased public awareness of the condition.[16]

Classification[edit]

ALS is a motor neuron disease, also spelled "motor neurone disease", which is a group of neurological disorders that selectively affect motor neurons, the cells that control voluntary muscles of the body.[2] Motor neuron diseases include amyotrophic lateral sclerosis (ALS), primary lateral sclerosis, progressive muscular atrophy, progressive bulbar palsy, pseudobulbar palsy, and spinal muscular atrophy.[2]

ALS itself can be classified a few different ways: by how fast the disease progresses (slow vs fast progressors), by whether it is inherited or sporadic, and by where it starts.[5] In about 25% of cases, muscles in the face, mouth, and throat are affected first, because motor neurons in the part of the brain stem called the medulla oblongata (formerly called the "bulb") start to die first along with lower motor neurons. This form is called "bulbar onset". In about 5% of cases muscles in the trunk of the body are affected first. In all cases the disease spreads and affects other regions.[4] The symptoms may also be limited to one spinal region.

Classical ALS, PLS, and PMA[edit]

ALS can be classified by the types of motor neurons that are affected. Typical or "classical" ALS involves neurons in the brain (upper motor neurons) and in the spinal cord (lower motor neurons).[17] Primary lateral sclerosis (PLS) involves only upper motor neurons, and progressive muscular atrophy (PMA) involves only lower motor neurons. There is debate over whether PLS and PMA are separate diseases or simply variants of ALS.[18]

Classic ALS accounts for about 70% of all cases of ALS and can be subdivided into spinal-onset and bulbar-onset ALS.[18] Spinal-onset ALS, also called limb-onset ALS, begins with weakness in the arms and legs[19] and accounts for about two-thirds of all cases of classic ALS.[18] Bulbar-onset ALS begins with weakness in the muscles of speech, chewing, and swallowing[17] and accounts for about one-third of all cases of classic ALS.[18] It is associated with a worse prognosis than spinal-onset ALS; a population-based study found that bulbar-onset ALS has a median survival of 2.0 years and a 10-year survival rate of 3%, while spinal-onset ALS has a median survival of 2.6 years and a 10-year survival rate of 13%.[20]

Primary lateral sclerosis (PLS) accounts for about 5% of all cases of ALS and affects upper motor neurons in the arms and legs.[21] However, more than 75% of people with apparent PLS develop lower motor neuron signs within four years of symptom onset, meaning that a definite diagnosis of PLS cannot be made until then.[22] PLS has a better prognosis than classic ALS, as it progresses slower, results in less functional decline, does not affect the ability to breathe, and causes less severe weight loss.[21]

Progressive muscular atrophy (PMA) accounts for about 5% of all cases of ALS and affects lower motor neurons in the arms and legs.[21] While PMA is associated with longer survival on average than classic ALS, it still progresses to other regions over time, eventually leading to respiratory failure and death.[18] Upper motor neuron signs can develop late in the course of PMA, in which case the diagnosis might be changed to classic ALS.[22]

Regional variants[edit]

Regional variants of ALS have symptoms that are limited to a single spinal cord region for at least a year; they progress slower than classic ALS and are associated with longer survival. Examples include flail arm syndrome, flail leg syndrome, and isolated bulbar ALS. Flail arm syndrome and flail leg syndrome are often considered to be regional variants of PMA because they only involve lower motor neurons. Isolated bulbar ALS can involve upper and/or lower motor neurons. These regional variants of ALS cannot be diagnosed at the onset of symptoms; a failure of the disease to spread to other spinal cord regions for an extended period of time (at least 12 months) must be observed.[23]

Flail arm syndrome, also called brachial amyotrophic diplegia,[a] is characterized by lower motor neuron damage in the cervical spinal cord only, leading to gradual onset of weakness in the proximal arm muscles and decreased or absent reflexes. Flail leg syndrome, also called leg amyotrophic diplegia,[b] is characterized by lower motor neuron damage in the lumbosacral spinal cord only, leading to gradual onset of weakness in the legs and decreased or absent reflexes. Isolated bulbar ALS is characterized by upper and/or lower motor neuron damage in the bulbar region only, leading to gradual onset of difficulty with speech (dysarthria) and swallowing (dysphagia); breathing (respiration) is generally preserved, at least initially. Two small studies have shown that people with isolated bulbar ALS may live longer than people with bulbar-onset ALS.[23]

Age of onset[edit]

ALS can also be classified based on the age of onset. While the peak age of onset is 58 to 63 for sporadic ALS and 47 to 52 for familial ALS,[4] about 10% of all cases of ALS begin before age 45 ("young-onset" ALS), and about 1% of all cases begin before age 25 (juvenile ALS).[17] People who develop young-onset ALS are more likely to be male, less likely to have a bulbar onset of symptoms, and more likely to have a slower progression of disease.[22] Juvenile ALS is more likely to be familial than adult-onset ALS; genes known to be associated with juvenile ALS include ALS2, SETX, SPG11, FUS, and SIGMAR1. Although most people with juvenile ALS live longer than those with adult-onset ALS, some of them have specific mutations in FUS and SOD1 that are associated with a poor prognosis.[24] Late onset (after age 65) is associated with a more rapid functional decline and shorter survival.[25]

Respiratory onset[edit]

Respiratory onset ALS is a rare variant that accounts for about 3% of all cases of ALS,[18] in which the initial symptoms are difficulty breathing (dyspnea) with exertion, at rest, or while lying down (orthopnea).[26] Spinal and bulbar symptoms tend to be mild or absent at the beginning. It is more common in males.[21] Respiratory onset ALS has the worst prognosis of any ALS variant; in a population-based study, those with respiratory onset had a median survival of 1.4 years and 0% survival at 10 years.[20]

Signs and symptoms[edit]

The disorder causes muscle weakness, atrophy, and muscle spasms throughout the body due to the degeneration of the upper motor and lower motor neurons. Individuals affected by the disorder may ultimately lose the ability to initiate and control all voluntary movement, although bladder and bowel function and the muscles responsible for eye movement are usually spared until the final stages of the disorder.[9]

Cognitive or behavioral dysfunction is present in 30–50% of individuals with ALS.[27] Around half of people with ALS will experience mild changes in cognition and behavior, and 10–15% will show signs of frontotemporal dementia.[9] Repeating phrases or gestures, apathy, and loss of inhibition are frequently reported behavioral features of ALS.[28] Language dysfunction, executive dysfunction, and troubles with social cognition and verbal memory are the most commonly reported cognitive symptoms in ALS; a meta-analysis found no relationship between dysfunction and disease severity.[29] However, cognitive and behavioral dysfunctions have been found to correlate with reduced survival in people with ALS and increased caregiver burden; this may be due in part to deficits in social cognition.[29] About half the people who have ALS experience emotional lability, in which they cry or laugh for no reason.[9]

Sensory nerves and the autonomic nervous system are generally unaffected, meaning the majority of people with ALS maintain hearing, sight, touch, smell, and taste.[5]

Initial symptoms[edit]

The start of ALS may be so subtle that the symptoms are overlooked.[5] The earliest symptoms of ALS are muscle weakness or muscle atrophy. Other presenting symptoms include trouble swallowing or breathing, cramping, or stiffness of affected muscles; muscle weakness affecting an arm or a leg; or slurred and nasal speech. The parts of the body affected by early symptoms of ALS depend on which motor neurons in the body are damaged first.[30]

In limb-onset ALS, people first experience awkwardness when walking or running or even tripping over or stumbling may be experienced and often this is marked by walking with a "dropped foot" which drags gently on the ground. Or if arm-onset, difficulty with tasks requiring manual dexterity such as buttoning a shirt, writing, or turning a key in a lock may be experienced.[30]

In bulbar-onset ALS, initial symptoms will mainly be of difficulty speaking clearly or swallowing. Speech may become slurred, nasal in character, or quieter. There may be difficulty in swallowing and loss of tongue mobility. A smaller proportion of people experience "respiratory-onset" ALS, where the intercostal muscles that support breathing are affected first.[4]

Over time, people experience increasing difficulty moving, swallowing (dysphagia), and speaking or forming words (dysarthria). Symptoms of upper motor neuron involvement include tight and stiff muscles (spasticity) and exaggerated reflexes (hyperreflexia) including an overactive gag reflex. An abnormal reflex commonly called Babinski's sign also indicates upper motor neuron damage. Symptoms of lower motor neuron degeneration include muscle weakness and atrophy, muscle cramps, and fleeting twitches of muscles that can be seen under the skin (fasciculations) although twitching is not a diagnostic symptom and more of a side effect so twitching would either occur after or accompany weakness and atrophy.[5]

Progression[edit]

Although the order and rate of symptoms vary from person to person, the disease eventually spreads to unaffected regions and the affected regions become more affected. Most people eventually are not able to walk or use their hands and arms, lose the ability to speak and swallow food and their own saliva, and begin to lose the ability to cough and to breathe on their own.[9]

The rate of progression can be measured using an outcome measure called the "ALS Functional Rating Scale Revised (ALSFRS-R)", a 12-item instrument administered as a clinical interview or self-reported questionnaire that produces a score between 48 (normal function) and 0 (severe disability);[31] it is the most commonly used outcome measure in clinical trials and is used by doctors to track disease progression.[32] Though the degree of variability is high and a small percentage of people have a much slower disorder, on average, people with ALS lose about 0.9 FRS points per month. A survey-based study among clinicians showed that they rated a 20% change in the slope of the ALSFRS-R as being clinically meaningful.[33]

Disorder progression tends to be slower in people who are younger than 40 at onset,[34] are mildly obese,[35] have disorder restricted primarily to one limb, and those with primarily upper motor neuron symptoms.[20] Conversely, progression is faster and prognosis poorer in people with bulbar-onset disorder, respiratory-onset disorder, and frontotemporal dementia.[20]

The CX3CR1 allelic variants have also been shown to have an effect on the disorder's progression and life expectancy.[36]

Late stages[edit]

Difficulty in chewing and swallowing makes eating very difficult and increases the risk of choking or of aspirating food into the lungs. In later stages of the disorder, aspiration pneumonia can develop, and maintaining a healthy weight can become a significant problem that may require the insertion of a feeding tube. As the diaphragm and intercostal muscles of the rib cage that support breathing weaken, measures of lung function such as vital capacity and inspiratory pressure diminish. In respiratory-onset ALS, this may occur before significant limb weakness is apparent. Most people with ALS die of respiratory failure or pneumonia.[4]

Although respiratory support can ease problems with breathing and prolong survival, it does not affect the progression of ALS. Most people with ALS die between two and four years after the diagnosis.[9] Around half of people with ALS die within 30 months of their symptoms beginning, and about 20% of people with ALS live between five and 10 years after symptoms begin.[4] Guitarist Jason Becker has lived since 1989 with the disorder, while cosmologist Stephen Hawking lived for 55 more years following his diagnosis, but they are considered unusual cases.[37]

Most people with ALS die in their own home, with their breath stopping while they sleep.[11]

Cause[edit]

Though the exact cause of ALS is unknown, genetic factors and environmental factors are thought to be of roughly equal importance.[38] The genetic factors are better understood than the environmental factors; no specific environmental factor has been definitively shown to cause ALS. A liability threshold model for ALS proposes that cellular damage accumulates over time due to genetic factors present at birth and exposure to environmental risks throughout life.[39]

Genetics[edit]

ALS can be classified as familial or sporadic, depending on whether or not there is a family history of the disease.[21] There is no consensus among neurologists on the exact definition of familial ALS. The strictest definition is that a person with ALS must have two or more first-degree relatives (children, siblings, or parents) who also have ALS. A less strict definition is that a person with ALS must have at least one first-degree or second-degree relative (grandparents, grandchildren, aunts, uncles, nephews, nieces or half-siblings) who also has ALS.[40] Familial ALS is usually said to account for 10% of all cases of ALS, though estimates range from 5%[41] to 20%.[42] Higher estimates use a broader definition of familial ALS and examine the family history of people with ALS more thoroughly.[40]

In sporadic ALS, there is no family history of the disease.[43] Sporadic ALS and familial ALS appear identical clinically and pathologically and are similar genetically;[42] about 10% of people with sporadic ALS have mutations in genes that are known to cause familial ALS.[18] In light of these parallels, the term "sporadic ALS" has been criticized as misleading because it implies that cases of sporadic ALS are only caused by environmental factors; the term "isolated ALS" has been suggested as a more accurate alternative.[42]

More than 20 genes have been associated with familial ALS, of which four account for the majority of familial cases:[44] C9orf72 (40%), SOD1 (20%), FUS (1–5%), and TARDBP (1–5%).[18] The genetics of familial ALS are better understood than the genetics of sporadic ALS;[18] as of 2016, the known ALS genes explained about 70% of familial ALS and about 15% of sporadic ALS.[45][46] Overall, first-degree relatives of an individual with ALS have a 1% risk of developing ALS.[38][47] ALS has an oligogenic mode of inheritance, meaning that mutations in two or more genes are required to cause disease.[48]

ALS and frontotemporal dementia (FTD) are now considered to be part of a common disease spectrum (FTD–ALS) because of genetic, clinical, and pathological similarities.[49] Genetically, C9orf72 repeat expansions account for about 40% of familial ALS and 25% of familial FTD.[48] Clinically, 50% of people with ALS have some cognitive and/or behavioral impairments and 5–15% have FTD, while 40% of people with FTD have some motor neuron symptoms and 12.5% have ALS.[18] Pathologically, abnormal aggregations of TDP-43 protein are seen in up to 97% of ALS patients and up to 50% of FTD patients.[50] Other genes known to cause FTD-ALS include CHCHD10, SQSTM1, and TBK1.[44]

Environmental factors[edit]

Where no family history of the disease is present — around 90% of cases — no cause is known. Possible associations for which evidence is inconclusive include military service and smoking.[27] Although studies on military history and ALS frequency are inconsistent, there is weak evidence for a positive correlation.[51] Various proposed factors include exposure to environmental toxins (inferred from geographical deployment studies), as well as alcohol and tobacco use during military service.[51]

A 2016 review of 16 meta-analyses concluded that there was convincing evidence for an association with chronic occupational exposure to lead; suggestive evidence for farming, exposure to heavy metals other than lead, beta-carotene intake, and head injury; and weak evidence for omega-three fatty acid intake, exposure to extremely low frequency electromagnetic fields, pesticides, and serum uric acid.[52]

In a 2017 study by the United States Centers for Disease Control and Prevention analyzing U.S. deaths from 1985 to 2011, occupations correlated with ALS deaths were white collar, such as in management, financial, architectural, computing, legal, and education jobs.[53] Other potential risk factors remain unconfirmed, including chemical exposure, electromagnetic field exposure, occupation, physical trauma, and electric shock.[54][55] There is a tentative association with exposure to various pesticides, including the organochlorine insecticides aldrin, dieldrin, DDT, and toxaphene.[56][57][58]

Head injury/trauma[edit]

A 2015 review found that moderate to severe traumatic brain injury is a risk factor for ALS, but whether mild traumatic brain injury increases rates was unclear.[59] A 2017 meta-analysis found an association between head injuries and ALS; however, this association disappeared when the authors considered the possibility of reverse causation, which is the idea that head injuries are an early symptom of undiagnosed ALS, rather than the cause of ALS.[60]

Physical activity[edit]

A 2005 systematic review found no relationship between the amount of physical activity and the risk of developing ALS, but did find that increased leisure time physical activity was strongly associated with an earlier age of onset of ALS.[61] A 2007 review concluded that physical activity was probably not a risk factor for ALS.[62] A 2009 review found that the evidence for physical activity as a risk factor for ALS was limited, conflicting, and of insufficient quality to come to a firm conclusion.[63] A 2014 review concluded that physical activity in general is not a risk factor for ALS, that American football and soccer are possibly associated with ALS, and that there was not enough evidence to say whether or not physically demanding occupations are associated with ALS.[64] A 2016 review found the evidence inconclusive and noted that differences in study design make it difficult to compare studies, as they do not use the same measures of physical activity or the same diagnostic criteria for ALS.[65]

Sports[edit]

Both soccer and American football have been identified as risk factors for ALS in several studies, although this association is based on small numbers of ALS cases.[66] A 2012 retrospective cohort study of 3,439 former NFL players found that their risk of dying from neurodegenerative causes was three times higher than the general US population, and their risk of dying from ALS or Alzheimer's disease was four times higher.[67] However, this increased risk was calculated on the basis of two deaths from Alzheimer's disease and six deaths from ALS out of 334 deaths total in this cohort, meaning that this study does not definitively prove that playing American football is a risk factor for ALS.[68] Some NFL players thought to have died from ALS may have actually had chronic traumatic encephalopathy (CTE), a neurodegenerative disorder associated with multiple head injuries that can present with symptoms that are very similar to ALS.[59]

Soccer was identified as a possible risk factor for ALS in a retrospective cohort study of 24,000 Italian soccer players who played between 1960 and 1996. There were 375 deaths in this group, including eight from ALS. Based on this information and the incidence of ALS, it was calculated that the soccer players were 11 times more likely to die from ALS than the general Italian population.[39] However, this calculation has been criticized for relying on an inappropriately low number of expected cases of ALS in the cohort.[63] When the lifetime risk of developing ALS was used to predict the number of expected cases, soccer players were no more likely to die of ALS than the general population.[39]

Smoking[edit]

Smoking is possibly associated with ALS. A 2009 review concluded that smoking was an established risk factor for ALS.[69] A 2010 systematic review and meta-analysis concluded that there was not a strong association between smoking and ALS, but that smoking might be associated with a higher risk of ALS in women.[70] A 2011 meta-analysis concluded that smoking increases the risk of ALS versus never smoking. Among smokers, the younger they started smoking, the more likely they were to get ALS; however, neither the number of years smoked nor the number of cigarettes smoked per day affected their risk of developing ALS.[71]

Pathophysiology[edit]

The defining feature of ALS is the death of both upper motor neurons (located in the motor cortex of the brain) and lower motor neurons (located in the brainstem and spinal cord).[72] In ALS with frontotemporal dementia, neurons throughout the frontal and temporal lobes of the brain die as well.[43] The pathological hallmark of ALS is the presence of inclusion bodies (abnormal aggregations of protein) in the cytoplasm of motor neurons. In about 97% of people with ALS, the main component of the inclusion bodies is TDP-43 protein;[19] however, in people with SOD1 or FUS mutations, the main component is SOD1 protein or FUS protein, respectively.[17] The gross pathology of ALS, which are features of the disease that can be seen with the naked eye, include skeletal muscle atrophy, motor cortex atrophy, sclerosis of the corticospinal and corticobulbar tracts, thinning of the hypoglossal nerves (which control the tongue), and thinning of the anterior roots of the spinal cord.[19]

It is still not fully understood why neurons die in ALS, but this neurodegeneration is thought to involve many different cellular and molecular processes.[18] The genes known to be involved in ALS can be grouped into three general categories based on their normal function: protein degradation, RNA processing, and the cytoskeleton.[43] Besides for the death of motor neurons, two other characteristics common to most ALS variants are focal initial pathology, meaning that symptoms start in a single spinal cord region, and progressive continuous spread, meaning that symptoms spread to additional regions over time.[17]

Excitotoxicity, or cell death caused by high levels of intracellular calcium caused by excessive activity of excitatory neurotransmitters, may be a mechanism of ALS. This concept has been supported by increased glutamate and dysfunctional glutamate transporterRNA in cerebrospinal fluid of those with ALS.[3] This is further supported by the only effective treatment being an anti-glutaminergic drug (Riluzole), as well as the poor ability to buffer calcium in motor neurons relative to other neurons.[73]

Neurofilament accumulation in axons has been observed in sporadic cases of ALS, as well as in SOD1 patients, possibly interfering with axonal transport, leading to cell death from SOD1 toxicity.[74]

Diagnosis[edit]

MRI (axial FLAIR) demonstrates increased T2 signal within the posterior part of the internal capsule, consistent with the diagnosis of ALS.

No test can provide a definite diagnosis of ALS, although the presence of upper and lower motor neuron signs in a single limb is strongly suggestive.[5] Instead, the diagnosis of ALS is primarily based on the symptoms and signs the physician observes in the person and a series of tests to rule out other diseases.[5] Physicians obtain the person's full medical history and usually conduct a neurologic examination at regular intervals to assess whether symptoms such as muscle weakness, atrophy of muscles, hyperreflexia, and spasticity are worsening.[5] A number of biomarkers are being studied for the condition, but so far are not in general medical use.[75][76]

Differential diagnosis[edit]

Because symptoms of ALS can be similar to those of a wide variety of other, more treatable diseases or disorders, appropriate tests must be conducted to exclude the possibility of other conditions.[5] One of these tests is electromyography (EMG), a special recording technique that detects electrical activity in muscles.[5] Certain EMG findings can support the diagnosis of ALS.[5] Another common test measures nerve conduction velocity (NCV).[5] Specific abnormalities in the NCV results may suggest, for example, that the person has a form of peripheral neuropathy (damage to peripheral nerves) or myopathy (muscle disease) rather than ALS. While a magnetic resonance imaging (MRI) is often normal in people with early stage ALS, it can reveal evidence of other problems that may be causing the symptoms, such as a spinal cord tumor, multiple sclerosis, a herniated disk in the neck, syringomyelia, or cervical spondylosis.[5]

Based on the person's symptoms and findings from the examination and from these tests, the physician may order tests on blood and urine samples to eliminate the possibility of other diseases, as well as routine laboratory tests.[5] In some cases, for example, if a physician suspects the person may have a myopathy rather than ALS, a muscle biopsy may be performed.[5]

Viral infectious diseases such as human immunodeficiency virus (HIV), human T-lymphotropic virus (HTLV), Lyme disease,[77] syphilis[78] and tick-borne encephalitis[79] can in some cases cause ALS-like symptoms.[5] Neurological disorders such as multiple sclerosis, post-polio syndrome, multifocal motor neuropathy, CIDP, spinal muscular atrophy, and spinal and bulbar muscular atrophy can also mimic certain aspects of the disease and should be considered.[5]

ALS must be differentiated from the "ALS mimic syndromes" which are unrelated disorders that may have a similar presentation and clinical features to ALS or its variants.[80] Because of the prognosis carried by this diagnosis and the variety of diseases or disorders that can resemble ALS in the early stages of the disease, people with ALS symptoms should always obtain a specialist neurological opinion in order to rule out alternative diagnoses. Myasthenic syndrome, also known as Lambert–Eaton syndrome, can mimic ALS, and its initial presentation can be similar to that of myasthenia gravis (MG), a treatable autoimmune disease sometimes mistaken for ALS.[81][82] Benign fasciculation syndrome is another condition that mimics some of the early symptoms of ALS, but is accompanied by normal EMG readings and no major disablement.[83]

Most cases of ALS, however, are correctly diagnosed, with the error rate of diagnosis in large ALS clinics is less than 10%.[84][85] One study examined 190 people who met the MND/ALS diagnostic criteria, complemented with laboratory research in compliance with both research protocols and regular monitoring. Thirty of these people (16%) had their diagnosis completely changed during the clinical observation development period.[86] In the same study, three people had a false negative diagnosis of MG, which can mimic ALS and other neurological disorders, leading to a delay in diagnosis and treatment. MG is eminently treatable; ALS is not.[87]

Management[edit]

There is no cure for ALS.[18] Management focuses on treating symptoms and providing supportive care, with the goal of improving quality of life and prolonging survival.[18] This care is best provided by multidisciplinary teams of healthcare professionals, and attending a multidisciplinary ALS clinic is associated with longer survival.[9] Riluzole prolongs survival by about 2-3 months.[7] Edaravone slows functional decline slightly in a small number of people with ALS;[88] it is expensive and must be administered by daily IV infusions that may decrease quality of life.[89] Other medications may be used to manage other symptoms.[90]

Non-invasive ventilation (NIV) is the main treatment for respiratory failure in ALS.[19] In people with normal bulbar function, it prolongs survival by about seven months and improves quality of life. One study found that NIV is ineffective for people with poor bulbar function[91] while another suggested that it may provide a modest survival benefit.[18] Many people with ALS have difficulty tolerating NIV.[92] Invasive ventilation is an option for people with advanced ALS when NIV is not enough to manage their symptoms.[9] While invasive ventilation prolongs survival, disease progression and functional decline continue.[93] It may decrease the quality of life of people with ALS and/or their caregivers.[94][93] Invasive ventilation is more commonly used in Japan than North America or Europe.[95]

Physical therapy can promote functional independence[96][97] through aerobic, range of motion, and stretching exercises.[90] Occupational therapy can assist with activities of daily living through adaptive equipment.[98] Speech therapy can assist people with ALS who have difficulty speaking.[97] Preventing weight loss and malnutrition in people with ALS improves both survival and quality of life.[18] Initially, difficulty swallowing (dysphagia) can be managed by dietary changes and swallowing techniques. A feeding tube should be considered if someone with ALS loses 5% or more of their body weight or if they cannot safely swallow food and water.[19] The feeding tube is usually inserted by percutaneous endoscopic gastrostomy (PEG). There is weak evidence that PEG tubes improve survival.[99] PEG insertion is usually performed with the intent of improving quality of life.[94]

Palliative care should begin shortly after someone is diagnosed with ALS.[100] Discussion of end-of-life issues gives people with ALS time to reflect on their preferences for end-of-life care and can help avoid unwanted interventions or procedures. Hospice care can improve symptom management at the end of life and increases the likelihood of a peaceful death.[94] In the final days of life, opioids can be used to treat pain and dyspnea, while benzodiazepines can be used to treat anxiety.[93]

Medications[edit]

Riluzole has been found to modestly prolong survival by about 2-3 months.[101][7] It may have a greater survival benefit for those with a bulbar onset.[7] Riluzole's mechanism of action is poorly understood. It may work by decreasing release of the excitatory neurotransmitter glutamate from pre-synaptic neurons.[19] The most common side effects are nausea and a lack of energy (asthenia).[7] People with ALS should begin treatment with riluzole as soon as possible following their diagnosis, according to guidelines from the European Federation of Neurological Societies.[100]

Edaravone has been shown to slow the decline in function (as measured by the Revised ALS Functional Rating Scale) in a small group of people with ALS who meet very strict criteria; there is no evidence that edaravone is effective in all people with ALS.[88] Its mechanism of action in ALS is unknown.[102] It may work by protecting motor neurons from oxidative stress.[103] The most common side effects are bruising and gait disturbance.[102] Treatment with edaravone is expensive (about $140,000 per year in the United States); it is also intensive and requires daily hour-long IV infusions for 10 days in a two-week period, followed by two weeks off the drug. Fatigue from these daily infusions or from daily travel to an infusion center may decrease quality of life.[89] There is debate over whether all people with ALS should receive edaravone.[21] People with ALS should be made aware of the time commitment, high cost, and limited therapeutic benefit before beginning treatment.[89]

Other medications may be used to help reduce fatigue, ease muscle cramps, control spasticity, and reduce excess saliva and phlegm. Drugs also are available to help people with pain, such as nonsteroidal anti-inflammatory drugs (NSAIDs) and opioids,[90] depression, sleep disturbances, dysphagia, and constipation. Baclofen and diazepam are often prescribed to control the spasticity caused by ALS, and trihexyphenidyl, amitriptyline or most commonly glycopyrrolate[3] may be prescribed when people with ALS begin having trouble swallowing their saliva.[9] A 2012 review found no evidence that medications are effective at reducing muscle cramps experienced by people with ALS; however, many of the 20 studies analyzed were too small to come to a definite conclusion about efficacy.[104] A 2017 review concluded that mexiletine was safe and effective for treating cramps in ALS based on a randomized controlled trial from 2016.[102]

Breathing support[edit]

Respiratory failure is the most common cause of death in people with ALS. It is caused by the progressive death of the motor neurons that control the muscles needed to breathe.[3] As these muscles weaken, several symptoms start to arise, including shortness of breath when undergoing physical activity or talking, fatigue, morning headaches, poor concentration and depression.[3]

Non-invasive ventilation[edit]

Non-invasive ventilation (NIV) is the primary treatment for respiratory failure in ALS[19] and was the first treatment shown to improve both survival and quality of life in people with ALS.[9] NIV uses a face or nasal mask connected to a ventilator that provides intermittent positive pressure to support breathing. Continuous positive pressure is not recommended for people with ALS because it makes breathing more difficult.[93] Initially, NIV is used only at night[9] because the first sign of respiratory failure is decreased gas exchange (hypoventilation) during sleep.[105]

It is important to monitor the respiratory function of people with ALS every three months, because beginning NIV soon after the start of respiratory symptoms is associated with increased survival. This involves asking the person with ALS if they have any respiratory symptoms and measuring their respiratory function.[9] The most commonly used measurement is upright forced vital capacity (FVC), but it is a poor detector of early respiratory failure and is not a good choice for those with bulbar symptoms, as they have difficulty maintaining a tight seal around the mouthpiece. Measuring FVC while the person is lying on their back (supine FVC) is a more accurate measure of diaphragm weakness than upright FVC.[92] Sniff nasal inspiratory pressure (SNIP) is a rapid, convenient test of diaphragm strength that is not affected by bulbar muscle weakness.[93] If someone with ALS has signs and symptoms of respiratory failure, they should undergo daytime blood gas analysis[9] to look for hypoxemia (low oxygen in the blood) and hypercapnia (too much carbon dioxide in the blood).[93] If their daytime blood gas analysis is normal, they should then have nocturnal pulse oximetry to look for hypoxemia during sleep.[9]

Non-invasive ventilation prolongs survival longer than riluzole. A 2006 randomized controlled trial found that NIV prolongs survival by about 48 days and improves quality of life; however, it also found that some people with ALS benefit more from this intervention than others. For those with normal or only moderately impaired bulbar function, NIV prolongs survival by about seven months and significantly improves quality of life. For those with poor bulbar function, NIV neither prolongs survival nor improves quality of life, though it does improve some sleep-related symptoms.[91] Despite the clear benefits of NIV, about 25–30% of all people with ALS are unable to tolerate it, especially those with cognitive impairment or bulbar dysfunction.[92] Results from a large 2015 cohort study suggest that NIV may prolong survival in those with bulbar weakness, and so NIV should be offered to all people with ALS, even if it is likely that they will have difficulty tolerating it.[18]

Invasive ventilation[edit]

Invasive ventilation bypasses the nose and mouth (the upper airways) by making a cut in the trachea (tracheostomy) and inserting a tube connected to a ventilator.[93] It is an option for people with advanced ALS whose respiratory symptoms are poorly managed despite continuous NIV use.[9] While invasive ventilation prolongs survival, especially for those younger than 60, it does not treat the underlying neurodegenerative process. The person with ALS will continue to lose motor function, making communication increasingly difficult and sometimes leading to locked-in syndrome, in which they are completely paralyzed except for their eye muscles.[93] About half of the people with ALS who choose to undergo invasive ventilation report a decrease in their quality of life[94] but most still consider it to be satisfactory. However, invasive ventilation imposes a heavy burden on caregivers and may decrease their quality of life.[93] Attitudes toward invasive ventilation vary from country to country; about 30% of people with ALS in Japan choose invasive ventilation, versus less than 5% in North America and Europe.[95]

Therapy[edit]

A man with ALS communicates with his wife by pointing to letters and words with a head mounted laser pointer.
A man with ALS communicates by pointing to letters and words using a head mounted laser pointer.

Physical therapy plays a large role in rehabilitation for individuals with ALS. Specifically, physical, occupational, and speech therapists can set goals and promote benefits for individuals with ALS by delaying loss of strength, maintaining endurance, limiting pain, improving speech and swallowing, preventing complications, and promoting functional independence.[96][97]

Occupational therapy and special equipment such as assistive technology can also enhance people's independence and safety throughout the course of ALS.[98] Gentle, low-impact aerobic exercise such as performing activities of daily living, walking, swimming, and stationary bicycling can strengthen unaffected muscles, improve cardiovascular health, and help people fight fatigue and depression. Range of motion and stretching exercises can help prevent painful spasticity and shortening (contracture) of muscles. Physical and occupational therapists can recommend exercises that provide these benefits without overworking muscles, because muscle exhaustion can lead to worsening of symptoms associated with ALS, rather than providing help to people with ALS.[90] They can suggest devices such as ramps, braces, walkers, bathroom equipment (shower chairs, toilet risers, etc.), and wheelchairs that help people remain mobile. Occupational therapists can provide or recommend equipment and adaptations to enable ALS people to retain as much safety and independence in activities of daily living as possible.[98]

People with ALS who have difficulty speaking may benefit from working with a speech-language pathologist.[97] These health professionals can teach people adaptive strategies such as techniques to help them speak louder and more clearly. As ALS progresses, speech-language pathologists can recommend the use of augmentative and alternative communication such as voice amplifiers, speech-generating devices (or voice output communication devices) or low-tech communication techniques such as head mounted laser pointers, alphabet boards or yes/no signals.[97]

Nutrition[edit]

Preventing weight loss and malnutrition in people with ALS improves both survival and quality of life.[18] Weight loss in ALS is caused by muscle wasting due to motor neuron death, increased resting energy expenditure, and decreased food intake. Difficulty swallowing (dysphagia) develops in about 85% of people with ALS at some point over the course of their disease and is a major cause of decreased food intake, leading to malnutrition and weight loss.[93] It is important to regularly assess the weight and swallowing ability of people with ALS.[9] Initially, dysphagia can be managed by dietary changes and modified swallowing techniques.[19] Difficulty swallowing liquids usually develops first and can be managed by switching to thicker liquids like fruit nectar or smoothies, or by adding fluid thickeners to thin fluids like water and coffee. People with ALS should eat soft, moist foods, which tend to be easier to swallow than dry, crumbly, or chewy foods.[105] They should also be instructed on proper head posture during swallowing, which can make swallowing easier.[19] There is tentative evidence that high-calorie diets may prevent further weight loss and improve survival.[102]

A feeding tube should be considered if someone with ALS loses 5% or more of their body weight or if they cannot safely swallow food and water.[19] This can take the form of a gastrostomy tube, in which a tube is placed through the wall of the abdomen into the stomach, or a nasogastric tube, in which a tube is placed through the nose and down the esophagus into the stomach.[93] A gastrostomy tube is more appropriate for long-term use[9] than a nasogastric tube, which is uncomfortable and can cause esophageal ulcers.[93] The feeding tube is usually inserted by percutaneous endoscopic gastrostomy (PEG). There is some evidence that a PEG tube should be inserted before vital capacity drops below 50% of expected, as a low vital capacity may be associated with a higher risk of complications. However, a large 2015 study showed that PEG insertion is safe in people with advanced ALS and low vital capacities, as long as they are on NIV during the procedure.[102]

There is weak evidence that PEG tubes improve survival.[99] PEG insertion is usually performed with the intent of improving quality of life[94] by sustaining nutrition and medication intake.[9] This reduces the risk of weight loss and dehydration, and can decrease anxiety from extended mealtimes[94] and decreased oral food intake.[9]

End-of-life care[edit]

Palliative care, which relieves symptoms and improves quality of life without treating the underlying disease, should begin shortly after someone is diagnosed with ALS.[100] Early discussion of end-of-life issues gives people with ALS time to reflect on their preferences for end-of-life care and can help avoid unwanted interventions or procedures.[94] Once they have been fully informed about all aspects of various life-prolonging measures, they can fill out advanced directives indicating their attitude toward noninvasive ventilation, invasive ventilation, and feeding tubes.[102] Late in the disease course, difficulty speaking due to muscle weakness (dysarthria) and cognitive dysfunction may impair their ability to communicate their wishes regarding care.[19] Continued failure to solicit the preferences of the person with ALS may lead to unplanned and potentially unwanted emergency interventions, such as invasive ventilation. If people with ALS or their family members are reluctant to discuss end-of-life issues, it may be useful to use the introduction of gastrostomy or noninvasive ventilation as an opportunity to bring up the subject.[94]

Hospice care, or palliative care at the end of life, is especially important in ALS because it helps to optimize the management of symptoms and increases the likelihood of a peaceful death.[94] It is unclear exactly when the end-of-life phase begins in ALS, but it is associated with significant difficulty moving, communicating, and, in some cases, thinking.[19] Although many people with ALS fear choking to death (suffocating),[94] they can be reassured that this occurs rarely, about 0–3% of the time. About 90% of people with ALS die peacefully.[106] In the final days of life, opioids can be used to treat pain and dyspnea, while benzodiazepines can be used to treat anxiety.[93]

Epidemiology[edit]

In much of the world, rates of ALS are unknown.[4] In Europe, the disease affects about 2.6 people per 100,000 per year.[10] In the United States, more than 5,600 are diagnosed every year (over 1.5 per 100,000 per year), and up to 30,000 Americans are currently affected. ALS is responsible for two deaths per 100,000 Americans per year.[107][108][109]

ALS is classified as a rare disease designated by the FDA as an "orphan" disease (affecting fewer than 200,000 people in the United States), but is the most common motor neuron disease. One or two of 100,000 people develop ALS each year.[110] ALS cases are estimated at 1.2–4.0 per 100,000 individuals in Caucasian populations with a lower rate in other ethnic populations.[111] People of all races and ethnic backgrounds may be affected. The disease can affect people at any age, but usually starts around the ages of 58 to 63 years for sporadic disease and 47 to 52 years for familial disease.[4][27]

History[edit]

Descriptions of the disease date back to at least 1824 by Charles Bell.[13]

In 1850, François-Amilcar Aran was the first to describe a disorder he named "progressive muscular atrophy", a form of ALS in which only the lower motor neurons are affected.[112]

In 1869, the connection between the symptoms and the underlying neurological problems were first described by Jean-Martin Charcot, who initially introduced the term amyotrophic lateral sclerosis in his 1874 paper.[13] Flail arm syndrome, a regional variant of ALS, was first described by Alfred Vulpian in 1886. Flail leg syndrome, another regional variant of ALS, was first described by Pierre Marie and his student Patrikios in 1918.[113]

ALS became a cause célèbre in the United States in 1939 when baseball legend Lou Gehrig's career, and two years later, his life, were ended by the disease.[114]

In 1945, American naval doctors reported that ALS was 100 times more prevalent among the Chamorro people of Guam than in the rest of the world. In 1956 the variant of ALS endemic to Guam was named "amyotrophic lateral sclerosis/parkinsonism dementia complex" (ALS/PDC), as it had the typical symptoms of ALS accompanied by parkinsonism-like symptoms; the name in the local language is lytico-bodig disease. Despite a number of genetic and environmental studies, the cause of ALS/PDC remains unknown. Rates peaked in the early 1950s and steadily declined thereafter, and by 1985 the incidence of ALS/PDC in Guam was about the same as the rest of the world.[115]

The first gene to be associated with ALS was SOD1, which was identified in 1993. It was the first time that linkage analysis was successful in identifying the genetic cause of a rare neurodegenerative disorder.[48]

In December 1995, riluzole became the first FDA-approved drug for ALS. It was then approved in Europe in 1996 and in Japan in 1998.[89]

In 1998, the El Escorial criteria were developed as the standard for classifying people with ALS in clinical research. The next year, the revised ALS Functional Rating Scale was published and soon becomes a gold standard for clinical research.[citation needed]

In 2006, it was discovered that the protein TDP-43 is a major component of the inclusion bodies seen in both ALS and frontotemporal dementia (FTD), which provided evidence that ALS and FTD are part of a common disease spectrum. This led to the discovery in 2008 that mutations in TARDBP, the gene that codes for TDP-43, are a cause of familial ALS.[48] In 2011, noncoding repeat expansions in C9orf72 were found to be a major cause of ALS and FTD.[19]

In 2013, the NFL reached a $765 million agreement to compensate more than five thousand former NFL players for concussion-related injuries and illnesses.[116] Some NFL players involved in the legal settlement complained that the NFL was not doing enough to help players. The judge in the case concurred, and in 2015 the NFL agreed to pay an unlimited amount of damages for players found to have ALS, Parkinson's disease, Alzheimer's disease, or dementia.[117]

Edaravone was approved to treat ALS in Japan and South Korea in 2015 and in the United States in 2017.[103] As of 2018, it has not been approved to treat ALS in Europe.[102]

Name[edit]

Amyotrophic comes from the Greek word amyotrophia: a- means "no", myo refers to "muscle", and trophia means "nourishment"; amyotrophia therefore means "no muscle nourishment," which describes the characteristic atrophy of the sufferer's disused muscle tissue. Lateral identifies the areas in a person's spinal cord where affected portions of the nerve cells are located. Degeneration in this area leads to scarring or hardening ("sclerosis").

In Commonwealth countries and Ireland, the term "motor neurone disease" (MND) is commonly used.[11]

ALS is sometimes referred to as "Charcot's disease" because Jean-Martin Charcot was the first to connect the clinical symptoms with the pathology seen at autopsy. The term is ambiguous and can also refer to Charcot–Marie–Tooth disease and Charcot joint disease.[118]

Society and culture[edit]

A student demonstrating the ice bucket challenge

In August 2014, a challenge went viral online, commonly known as the "ALS Ice Bucket Challenge".[119] Contestants fill a bucket full of ice and water, then state who nominated them to do the challenge, and nominate three other individuals of their choice to take part in it. The contestants then dump the buckets of ice and water onto themselves. However, it can be done in a different order. The contestants then donate at least US$10 (or a similar amount in their local currency) to ALS research at the ALS Association, the ALS Therapy Development Institute, ALS Society of Canada or Motor Neurone Disease Association in the UK. Any contestants who refuse to have the ice and water dumped on them are expected to donate at least US$100 to ALS research. As of July 2015, the Ice Bucket Challenge had raised $115 million for the ALS Association.[120] Many celebrities have taken part in the challenge.[121] The Ice Bucket Challenge was credited with helping to raise funds that contributed to the discovery that the gene NEK1 may potentially contribute to the development for ALS.[122][123]

Research[edit]

Treatments[edit]

Repetitive transcranial magnetic stimulation had been studied in ALS in small and poorly designed clinical trials; as of 2013, evidence was insufficient to know whether rTMS is safe or effective for ALS.[124]

One 2016 review of stem-cell therapy trials found tentative evidence that intraspinal stem cell implantation was relatively safe and possibly effective.[125] A 2016 Cochrane review of cell based therapies found that there was insufficient evidence to speculate about efficacy.[126] Stem cell therapy can provide additional proteins and enzymes that have shown to help prolong survival and control the symptoms associated with ALS.[90][127] Those proteins include neurotrophic factors and insulin-like growth factor 1. Both those proteins are still under clinical trials and need to be further studied to evaluate their efficiency and associated side effects.[90][127]

Masitinib has been approved as an orphan drug in Europe and the United States, with studies ongoing as of 2016.[128] Medications tested, but without evidence for efficacy include lamotrigine, dextromethorphan, gabapentin, BCAAs, Vitamin E, acetylcysteine, selegiline, amantadine, cyclophosphamide, various neurotrophic factors, which has shown promise in both in vitro and in vivo models of ALS, but is yet to be effective in human models of ALS[90][127][74] and creatine.[129] Beta-adrenergic agonist drugs have been proposed as a treatment for their effects on muscle growth and neuroprotection, but research in humans is insufficient to determine their efficacy.[130]

Cause[edit]

With the discovery that TDP-43, FUS, and C9orf72 can cause ALS as well as related forms of frontotemporal dementia (FTD/ALS)[131][132] there has been intense effort to understand how these mutations cause disease, and whether other protein dysfunction may be important. As of 2013 it appeared that differences in the methylation of arginine residues in FUS protein may be relevant, and methylation status may be a way to distinguish some forms of FTD from ALS.[133]

Notes[edit]

  1. ^ Additional names for flail arm syndrome include the scapulohumeral form of ALS, Vulpian–Bernart syndrome, hanging arm syndrome, and neurogenic man-in-a-barrel syndrome.[21]
  2. ^ Additional names for flail leg syndrome that involves both lower legs (bilateral distal involvement) include pseudopolyneuritic ALS, Patrikios syndrome, Marie-Patrikios ALS, and the peroneal form of ALS.[21]

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