ALS can cause a wide variety of symptoms in an individual. Primary symptoms, including spasticity, muscle weakness and atrophy, and fasciculations are a direct result of motor neurons in the body being diseased. Other symptoms, such as difficulty breathing or speaking are caused by those primary symptoms.
Atrophy: the decrease in size or wasting of a body part.
Bulbar system: a group of structures in the brainstem that are involved in several essential functions, including motor control and autonomic regulation. The term "bulbar" refers to the medulla oblongata of the brain, which is shaped like a bulb.
Dysarthria: speech issues caused by weakness, paralysis, or lack of coordination of the muscles involved in speech production. It affects the physical production of speech.
Dysphagia: difficulty or discomfort in swallowing.
Dysphonia: a disorder of the voice, specifically relating to problems with voice production. It involves issues with the vocal folds (vocal cords) or the structures that control them.
Dyspnea: shortness of breath.
Fasciculations: involuntary movement of the muscles.
Hyperreflexia: an increased or overactive reflex response.
Motor neuron: a type of cell in the body that is responsible for transmitting signals from the brain to the muscles.
Orthopnea: difficulty breathing when lying down.
Spasticity: muscle rigidity or “stiffness”.
Spasticity is caused by the motor neurons in the brain persistently sending a contraction signal to a muscle. This causes the affected muscles to feel tight, or stiff.
Spasticity may be most noticeable at a certain time of day, such as before bed, or overnight. Some individuals with ALS find that it is at its strongest first thing in the morning.
I would sometimes wake up with stiff calf muscles. They would relax shortly after waking. If I fell back asleep and then woke back up, that whole process would happen again.
— Male diagnosed with ALS at age 38
Muscles require a connection to healthy motor neurons to live. Muscles will eventually atrophy without such connections, which will cause weakness and eventual paralysis.
As ALS affects more and more motor neurons, the muscles which they are connected to will atrophy more and more.
Muscle weakness and atrophy is the reason why ALS is fatal. The body relies on movement caused by muscles for several essential tasks, such as breathing.
Damaged motor neurons may suddenly stop sending a signal to the muscle that they innervate when they are put under significant strain. ALS patients can experience a sudden, unexpected loss of strength in a muscle during activation. Such an occurrence may cause stumbling while walking or dropping something that is being held. Rarely, the muscle may become completely paralyzed for a brief moment if it is put under significant strain.
I was adjusting some of the spokes on a bicycle wheel, which was putting a lot of stress on my fingers. Suddenly the index finger and thumb on my left hand were no longer able to pinch toward each other; I had no use of them at all. This lasted for a few seconds, and then mobility returned to normal.
— Male diagnosed with ALS at age 38
Muscle weakness and atrophy may first become noticeable in one of three regions of the body: the limbs, the bulbar system, or the respiratory system. Limb-onset is the most common; respiratory-onset is the least.
With bulbar-onset weakness, difficulty chewing and swallowing, or changes to voice pitch or clarity may be observed as the first symptom.
With respiratory-onset weakness, difficulty breathing while lying down may be observed as the first symptom.
With limb-onset weakness, the first location of weakness may be observed in a wide number of places. Typically, however, muscles furthest away from the trunk of the body are affected first (i.e. hands and wrists, feet and ankles). Muscles closer to the trunk of the body will become affected as the disease progresses.
Many hand movements are powered by muscles located in the forearm. Narrow tendons pass through the wrist's carpal tunnel and connect to the fingers. For instance, the muscles responsible for curling the fingers—like when holding a heavy bucket or briefcase—are found in the forearm. In contrast, the muscles used for pinching between the index finger and thumb are located in the hand itself. This muscle arrangement explains why individuals with ALS often lose pinch strength before they lose the ability to grasp objects.
An individual may experience muscle weakness and atrophy in one or more muscles that are closer to the trunk of their body, while other more distant muscles remain unaffected. Additionally, each person has varying levels of strength in different muscle groups. For instance, someone might have relatively weak shoulder muscles, which could lead to issues before they notice any problems in their hands or other areas.
Table: first observable signs of muscle weakness | |
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Onset location | Signs |
Bulbar |
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Respiratory |
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Lower limbs |
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Upper limbs |
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Fasciculations in ALS are caused by damaged motor neurons sending signals to the muscles involuntarily.
Fasciculations caused by ALS can present in any muscle that is innervated by motor neurons that have been damaged by the disease. This can include almost any muscle in the body, even the muscles found around the ears. Fasciculations in large muscles, such as quadriceps, biceps, and triceps can be visible to the naked eye.
Fasciculations may vary in intensity throughout the course of the day, and may even be affected by consumption of food. Fasciculations caused by ALS tend to become significant shortly after intense exercise and will gradually fade away. Fasciculations may at times be strong enough to cause involuntary muscle movement, especially of fingers and toes due to their small size.
Fasciculations in a given muscle can be stopped or at least reduced by voluntarily contracting the muscle. Conversely, relaxing a muscle may make fasciculations more noticeable; this may especially be an issue when lying down to sleep. The intensity of fasciculations may increase as ALS progresses, however, as the muscles continue to atrophy, the disruptive nature of fasciculations will decrease.
Fasciculations caused by ALS are not typically harmful; however, they can disturb sleep, and cause other difficulties. Individuals experiencing fasciculations without a known cause may experience anxiety as they fear that the cause may be something serious.
Intense exercise such as weightlifting frequently causes twitching and spasms, but these present differently than fasciculations caused by ALS. Exercise-induced twitches and spasms can generally be eased with rest and hydration.
It was common for me to experience twitches and spasms after going to the gym. Fasciculations from ALS do not feel the same at all, at least not to me. The usual twitches and spasms would often happen hours or days after working out, compared to fasciculations from ALS, which would present almost right away and then gradually fade away over the span of many hours.
I would describe the post-workout twitches and spasms as being "concentrated in a small area", "quick", and "sudden", whereas fasciculations from ALS are more "widespread", "wave-like", and "consistent".
– Man diagnosed with ALS at age 38
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Secondary symptoms of ALS are symptoms that are consequences of muscle weakness and atrophy, or spasticity. Muscles which support essential functions, such as breathing, must be strong enough to fulfil their duties.
Muscles in healthy individuals are typically far stronger than they need to be; considerable atrophy may take place before any decline in function is observed.
ALS is often described as "painless". Such a statement is accurate from a neurological perspective: sensory nerves are not affected by ALS, and the absence of nerve compression or other damage would further suggest an absence of pain. However, spasticity may be painful, as can significant muscle atrophy when it has occurred in places such as the legs or hands. Muscles in the human body act as cushions; when they have atrophied, they are no longer able to provide a level of cushioning required to avoid feelings of pain when pressure is applied to that part of the body.
In later stages of ALS, when the individual is unable to adjust their position when in chairs or in bed, will eventually experience bedsores. Bedsores are painful, as the name clearly suggests.
Dyspnea and orthopnea are caused by a weak diaphragm muscle, which is responsible for breathing. It is more difficult for the diaphragm to work against the chest cavity when in a supine position compared to a more upright position.
Difficulties with breathing reflexes such as coughing and sneezing become present when the diaphragm muscle and other muscles associated with these reflexes become weaker.
Retention and voluntary expulsion of urine is a complex process. Between the neck of the bladder and the perineal membrane lies a sphincter complex made of two independent sphincters. The external sphincter is made of striated skeletal muscle, much like muscles of the limbs, and is regulated voluntarily. The internal urethral sphincter is made of smooth muscle and is regulated involuntarily.
Urinary incontinence refers to the inability to retain urine. Retention of urine in the bladder relies on the contraction of the internal sphincter. If it is not sufficiently able to contract, urine will pass through the sphincter. In ALS, this situation arises with atrophy of the sphincter muscles.
Urinary retention refers to the inability to expel urine voluntarily. Retention will occur if the muscles of the urinary sphincter complex are unable to relax. In ALS, this situation arises with spasticity of the sphincter muscles.
https://www.ncbi.nlm.nih.gov/books/NBK482438/
Acid reflux, also known as heartburn, or gastroesophageal reflux, is when the upper esophageal sphincter relaxes enough to allow stomach acid to enter the esophagus.
ALS is known to cause spasticity and atrophy of the upper esophageal sphincter, though is often much less than that of the lower esophageal muscles. Still, some ALS patients will undergo a surgical procedure called cricopharyngeal myotomy, which involves making an incision in the cricopharyngeal muscle to allow it to relax more easily, which aids with swallowing.
Acid reflux is also a common consequence of aging; acid reflux may present itself in an ALS patient independent of the disease itself. ALS patients may make dietary adjustments to simplify swallowing; these adjustments may themselves cause acid reflux to occur.
Acid reflux symptoms may be worse when lying down; these symptoms may be mitigated by lying on the left side. This places the upper esophageal sphincter in a more upright position, and places the stomach lower down. Conversely, lying on the right side elevates the stomach and points the upper esophageal sphincter downward, which promotes leakage.
Constipation as it pertains to ALS is caused by any of the following:
Treatment of constipation in ALS patients involves increased fluid intake, further changes to diet, and adjustments to medications and their dosages.
Extreme cases of constipation may require manual intervention of a bowel movement via rectal irrigation, a procedure where warm water is introduced into the rectum, causing the waste to break free and evacuate.
Pelvic floor muscles associated with sexual function, such as those responsible for erections and ejaculation in men are resilient against the effects of neurodegeneration in ALS. The motor neurons innervating these muscles are of a different type from other muscles in the body.
https://pubmed.ncbi.nlm.nih.gov/6499298/
Speech difficulties, known as dysphonia, is caused by atrophy of the muscles of the mouth, throat, and voice box.
Large muscles of the face, such as those that raise or lower the eyebrows, are affected by ALS and will eventually suffer from weakness and atrophy. Difficulty smiling, winking, and so forth negatively affects nonverbal communication capability.
Chewing difficulties are caused by atrophy of muscles in and around the mouth.
Dysphagia in ALS caused by atrophy of muscles of the mouth and throat.
Drooling, also known as sialorrhea, is excess flow of saliva.
In ALS, drooling is caused by the the following:
In ALS, drooling is not a consequence of excess production of saliva; it is only a consequence of the changes in retention and evacuation characteristics. Nonetheless, treatments for drooling experienced by ALS patients are focused on reducing production of saliva to provide symptomatic relief.
Treatments for drooling experienced by ALS patients include:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6498144
Dry mouth in ALS is caused by breathing through the mouth instead of the nose. Mouth breathing itself is caused by weakening of the muscles in the face, which prevent the mouth from closing, making it the path of least resistance for airflow when breathing.
Oral thrush, or candidiasis, sometimes known as a yeast infection of the mouth, is more likely to occur in ALS patients that breathe through their mouths.
Research studies have observed eye movement abnormalities in some ALS patients. The findings of these studies remain controversial and inconclusive.
Epiphora, the excess production of tears, is not associated with ALS.
The orbicularis oculi and lavetor palpabrae muscles, responsible for closing and opening the eyelid respectively, are rarely affected by ALS.
Hearing is preserved in individuals with ALS.
Edema (swelling of the limbs) may become present in the middle and later stages of ALS. Prolonged sitting, a lack of limb movement, and compression of veins due to muscle atrophy all contribute to edema in ALS patients.
Edema is typically treated by the use of compression socks; most individuals with ALS require assistance to put them on.
See also: Occupational Therapy: Sleeping
Sleep difficulties are common and are a consequence of breathing difficulties, muscle weakness, and muscle atrophy.
Muscle weakness makes it difficult to roll over and make other small adjustments; muscle atrophy makes sleep less comfortable as a result of the limbs and other parts of the body becoming bony.
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A diagnosis of ALS will surely affect an individual's priorities, perspectives and behaviors. Such changes may include irritability, frustration, or a loss of inhibition; these are not caused by ALS itself, but rather from the predicament of having to live with a terminal disease.
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