Neuromuscular disorders cause major changes in an individual's daily ability to function and thus their independence. A neuromuscular disorder or disease is a broad term encompassing a large variety of diseases with different presentations. As healthcare evolves, so does clinical research, updating disease diagnostic criteria and treatment options for neuromuscular disorders. This series will discuss neuromuscular disorders from a health science point of view concerning etiology, pathophysiology, and treatment of neuromuscular disorders. The series will also discuss in depth the types of disorders and their etiology, diagnosis criteria, and medical rehabilitation management.
The series is divided into the following eight chapters:
Neuromuscular Disorders 101: The Effects of Amyotrophic Lateral Sclerosis
Neuromuscular Disorders 101: Charcot-Marie-Tooth Disease: Effects on Childhood to Adulthood
Neuromuscular Disorders 101: The Dysfunction of Multiple Sclerosis
Neuromuscular Disorders 101: In the Face of Myasthenia Gravis
Neuromuscular Disorders 101: Infection to Impairment: Guillain-Barre Syndrome
Neuromuscular Disorders 101: The Effects of Amyotrophic Lateral Sclerosis
Amyotrophic Lateral Sclerosis (ALS) is a neuromuscular disease that involves the progressive damage and loss of function in motor neurons in the brain and spinal cord (Guy-Evans, 2021; Hulisz, 2018). The damage ALS causes to the nervous system ultimately leads to paralysis, or loss of movement in all or some body parts. The cause of ALS is largely unknown, however it affects between 4.1 to 8.4 out of 100,000 people (Longinetti & Fang, 2019). Overall, approximately 16,000 individuals in the U.S. are suffering from ALS, with 6,000 new cases being diagnosed each year (Hulisz, 2018). In this 101 series article, we will discuss the pathophysiology, diagnostic measures, and treatment associated with ALS.
Motor neurons act like telephone poles that send and receive messages from the brain and spinal cords to muscles sending the signal to perform tasks such as breathing, swelling, and moving specific body parts, for example lifting up your arm. Motor neurons are divided into two categories: upper motor neurons (UMN) and lower motor neurons (LMN) (Hulisz, 2018). UMN are located inside the brain, specifically in the motor cortex. Their function is to send messages from the brain to initiate and mediate voluntary movement (Emos & Agarwal, 2022). LMN are located in the spinal cord and lower portion of the brainstem and serve as the ‘receivers’ of these messages sent by UMN. Once a message is received, LMN transmit these messages to the intended musculature to perform a movement (Zayia & Tadi, 2022). In ALS, UMN and LMN are damaged, which stops them from sending messages to the muscles, which causes loss of mobile function (“Amyotrophic Lateral Sclerosis”, n.d.).
About 5% to 10% of ALS cases are caused by inheritance of a gene mutation, and is known as familial ALS. Genes are made from parts of deoxyribonucleic acid, better known as DNA. DNA could be considered akin to instructions for making proteins. A gene mutation is an error in a DNA sequence which causes a cell to make excess of a protein, make less of a protein, or a malfunctioning protein (“The Genetics of ALS”, n.d.). Genes are portions of DNA that sit along a chromosome, which are inherited from each parent.. Despite the unknown genetic complexity behind familial ALS, studies have shown that it is usually due to a dominant trait, in which only one mutated copy is needed to cause ALS. (Hulisz, 2018; “The Genetics of ALS”, n.d.).
According to John Hopkins Medicine (n.d.), sporadic ALS is defined as a random occurrence of the disease with no known cause and no family history of ALS. This is the most common form of the disease, with 90% to 95% of all cases diagnosed as sporadic ALS (“The Genetics of ALS”, n.d.).
Signs and Symptoms
Symptoms of ALS vary depending on what exact motor neurons are damaged at time of onset. Damage in UMN causes dysfunction in coordination of body parts and stiffness in muscles versus muscle twitching and muscle wasting caused by LMN damage (Hulisz, 2018). However, generally ALS begins with muscle weakness that becomes progressively worse over time (“Amyotrophic Lateral Sclerosis”, n.d.). ALS is seen first in the hands, feet, legs/arms, with symptoms such as dropping objects, tripping/falling, and difficulty walking. As ALS spreads to other muscles in the body, symptoms of slurred speech, swallowing and breathing difficulty, and cognitive changes start to become apparent. Due to ALS's progressive paralyzing effect in the respiratory muscles, respiratory failure begins to occur which later leads to death. (“Amyotrophic Lateral Sclerosis”, n.d.). Advanced ALS cases usually have a tracheostomy performed (surgical hole at the front of the neck leading to the windpipe or trachea) to inflate and deflate their lungs to assist with breathing. A feeding tube may also have to be put in place in people with advanced cases due to ineffective swallowing due to muscle weakness, which can cause malnutrition and dehydration. Studies have also shown ALS to affect the heart as the organ is a muscle itself (Rosenbohm, 2017). It has been reported the disease alters heart rate and potentially causes sudden cardiac arrest in patients with ALS.
Mayo Clinic (n.d.) describes the variety of risk factors associated with ALS:
Heredity: Five to 10 percent of the people with ALS inherited it (familial ALS). In most people with familial ALS, their children have a 50-50 chance of developing the disease.
Age: ALS risk increases with age, and is most common between the ages of 40 and the mid-60s.
Sex: Before the age of 65, slightly more men than women develop ALS. This sex difference disappears after age 70.
Genetics: Some studies examining the entire human genome found many similarities in the genetic variations of people with familial ALS and some people with non inherited ALS. These genetic variations might make people more susceptible to ALS.
Smoking: Smoking is the only likely environmental risk factor for ALS. The risk seems to be greatest for women, particularly after menopause.
Environmental toxin exposure: Some evidence suggests that exposure to lead or other substances in the workplace or at home might be linked to ALS. Much study has been done, but no single agent or chemical has been consistently associated with ALS.
Military service: Studies indicate that people who have served in the military are at higher risk of ALS. It is unclear why military service might trigger the development of ALS. It might include exposure to certain metals or chemicals, traumatic injuries, viral infections, and intense exertion.
Diagnostic tests specific for ALS are currently non-existent, and therefore ALS is diagnosed by symptoms of UMN and/or LMN damage followed by progressive muscle weakness in other body parts (Ralli et al., 2019). Due to ALS’ mysterious and progressive onset of symptoms, diagnosis is often delayed 9 to 12 months after initial symptom onset (Hulisz, 2018). The survival rate of individuals with ALS is 2 to 5 years from disease onset (“Amyotrophic Lateral Sclerosis”, n.d.; Hulisz, 2018). A majority of testing for ALS is performed to rule out other neuromuscular disorders to confirm an ALS diagnosis. The National Institute of Neurological Disorders and Stroke (NINDS) (n.d.) detail diagnostic tests utilized in ALS diagnosis as follows:
Electromyography (EMG) is a recording technique that detects electrical activity of muscle fibers and can help diagnose ALS.
A nerve conduction study (NCS) measures the electrical activity of your nerves and muscles by assessing the nerve's ability to send a signal along the nerve or to the muscle.
Magnetic resonance imaging (MRI) is a non-invasive procedure that uses a magnetic field and radio waves to produce detailed images of the brain and spinal cord.
Blood and urine tests may be performed based on symptoms, test results, and findings from the examination by a doctor. They may order these tests to eliminate the possibility of other diseases.
A muscle biopsy may be performed if your doctor suspects a muscle disease other than ALS. Under local anesthesia, a small sample of muscle is removed and sent to the lab for analysis.
There is no known cure for ALS. Medical management is geared towards preserving quality of life and attempting to slow down the progression of the disease. Rehabilitation therapy plays a huge role in the treatment of ALS to maintain cardiovascular function, muscle strength, and range of motion of body parts (“Amyotrophic Lateral Sclerosis”, n.d). Studies have shown that therapeutic physical exercise consisting of endurance conditioning, low-impact aerobic exercise, strength training, and stretching demonstrate benefits over both the short and long term (2 weeks to 6 months) (“Amyotrophic Lateral Sclerosis”, n.d; Ortega-Hombrados et al., 2021). A pharmacological intervention for ALS is Riluzole, serving to delay the amount of time before one needs to undergo a tracheostomy due to ALS’ effects on the respiratory system.It is speculated that Riluzole’s affect to delay progressive ALS symptoms is due to the inhibitory effect it has on controlling glutamate release in the body, which has potential to damage motor neurons (“Riluzole”, n.d.). Glutamate is an excitatory neurotransmitter, or a chemical signal that sends messages from a neuron to a specific cell (e.i. Muscle cell) (“Neurotransmitters”, n.d.).
A case study reported by Houseman and Kelly (2005) describes the treatment of a 53 year old male who developed signs of muscular weakness, specifically left foot drop, who was later diagnosed with ALS a year later after further symptom onset. A chief complaint of the patient was difficulty breathing, which had gotten progressively worse over time. The patient was also experiencing neurological symptoms: weakness in hands and arms, foot drop, mild difficulty with speech and swallowing. The patient’s clinical visits consisted of treatment strategies to maintain function such as ankle-foot orthotics, swallowing exercises and lifestyle changes such as changing his diet to soft foods. The medical team examined the patient’s respiratory symptoms by observing oxygen levels while the patient was sleeping. The results of the monitor qualified the patient for assisted respiratory device use which showed an improvement in the patient’s respiratory status after two months of use. The authors highlight the importance of respiratory care in patients with ALS through a thorough assessment to include questioning on difficulty breathing at rest, minimal activity, and during sleep.
ALS is a progressive debilitating disease that creates a major impact on quality of life and independence. Most cases of ALS are diagnosed as sporadic ALS caused by an insidious onset of neuromuscular symptoms. Early symptoms of ALS include muscle twitching and cramps, stiffness and weakness in musculature, and difficulty swallowing and breathing (“Amyotrophic Lateral Sclerosis”, n.d). As the disease progresses, daily function and mobility deteriorate, as many people with ALS lose the ability to stand, walk, breathe, swallow, and/or use their limbs. Although prognosis in this disease is grim, rehabilitation therapy, breathing care, and continued physical activity have been shown effective in conservative management to delay disease progression (“Amyotrophic Lateral Sclerosis”, n.d.; Hulisz, 2018; Riluzole”, n.d.). This supportive care provided by a multidisciplinary team consisting of physicians, pharmacists, physical/occupational/speech therapists, respiratory therapists, and nutritionists allow individuals affected with ALS receive an individualized treatment plan to maintain mobility function and independence as much as one can. ALS’ progressive damage to the musculature in later stages of the disease cause patients to rely on assistive devices such as a power wheelchair and respiratory ventilator to maintain function and survival before eventually dying of respiratory/cardiac failure. Research is still at ongoing concerning advances in disease etiology, specific therapeutic prescription guidelines and potential disease reversal treatment options. Current efforts in ALS research are focused on identifying disease mechanisms at a cellular level as well as the role genetics play in the disease (“Amyotrophic Lateral Sclerosis”, n.d). For example the NINDS (n.d.) have begun to utilize stem cells to investigate human spinal cord areas to create a better understanding of neuron function in ALS body tissues.
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Figure 1: Burke-Doe, A. (n.d.). Motor pathways. [Image]. Retrieved February 8, 2023 from https://accessphysiotherapy.mhmedical.com/data/Multimedia/grandRounds/motorpathways/media/motorpathways_print.html
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Figure 3: ALS Progression Timeline. (n.d.). ALS Treatment. [Image]. Retrieved February 8, 2023 from https://alstreatment.com/als-progression-timeline/