Description, Causes and Risk Factors:
Neurodegeneration are a group of progressive neurological disorders that destroy motor neurons, the cells that control essential voluntary muscle activity such as speaking, walking, breathing, and swallowing. Normally, messages from nerve cells in the brain (called upper motor neurons) are transmitted to nerve cells in the brain stem and spinal cord (called lower motor neurons) and from them to particular muscles. Upper motor neurons direct the lower motor neurons to produce movements such as walking or chewing. Lower motor neurons control movement in the arms, legs, chest, face, throat, and tongue. Spinal motor neurons are also called anterior horn cells. Upper motor neurons are also called corticospinal neurons.
When there are disruptions in the signals between the lowest motor neurons and the muscle, the muscles do not work properly; the muscles gradually weaken and may begin wasting away and develop uncontrollable twitching (called fasciculation). When there are disruptions in the signals between the upper motor neurons and the lower motor neurons, the limb muscles develop stiffness (called spasticity), movements become slow and effortful, and tendon reflexes such as knee and ankle jerks become overactive. Over time, the ability to control voluntary movement can be lost.
Scientists are not sure why motor neurons start to lose function. They believe several inter-related factors cause neurodegeneration, including:
Excess glutamate - glutamate is a neurotransmitter, a messenger chemical that transmits data from cell-to-cell. Some studies indicate that people with neurodegeneration have too much glutamate. Abnormally high levels of glutamate may be toxic and could lead to a disturbance in the chemical communication required for good nerve function.
Cell metabolism - transport systems exist in all cells that bring nutrients and chemical components into the cell, while at the same time moving waste products out. Scientists say there are indications that these transport systems are disturbed in the motor neurons during the initial stages of neurodegeneration, resulting in poor nerve function.
Aggregates - unusual clumps of protein molecules have been found to accumulate in the motor neurons of neurodegenerative patients. Scientists believe these aggregates undermine the normal functioning of motor neurons.
Lack of antioxidant production - research indicates that the motor neurons of patients with neurodegeneration do not produce enough antioxidants to neutralize the free radicals that emerge as a natural by-product of cell activity. Oxygen-free radicals are a type of toxic waste cells produce - antioxidants mop them up.
Mitochondria of motor neurons - research has found that the mitochondria of motor neuron cells of people with neurodegeneration appear to be abnormal. Mitochondria provide the energy cells need to carry out their normal function - they are normal structures responsible for energy production in cells.
Neurotrophic factors - these are molecules, usually proteins, that facilitate the growth or repair of nerve cells. It has been found that neurotrophic factors are not produced properly in patients with neurodegeneration, making the motor neurons more susceptible to damage.
Glia cells - these cells surround neurons and provide support for them and insulation between them. They also provide motor neurons with nutrients and relay data from one cell to another. In some cases, problems with glia cells can affect the motor neurons.
Prions and ALS link - Researchers discovered a vital link between prions and amyotrophic lateral sclerosis (ALS). The scientists explained that SOD1 (superoxide dismutase 1), which studies have demonstrated is involved in the progress of ALS, exhibits prion-like properties. SOD1 is involved in a process called template-directed misfolding.
Prognosis varies depending on the type of neurodegeneration and the age of onset. Some neurodegeneration, such as ALS and some forms of SMA (spinal muscular atrophy) are fatal.
The patient's grip weakens. Sometimes picking up and/or holding things can be difficult.
Slurred and sometimes garbled speech.
Weakness in the limbs.
Blood and urine tests - by analyzing samples of the patient's blood and urine in the lab the doctor can rule out other possible causes for the signs and symptoms. A blood test can also determine whether there is any rise in creatinine kinase, which can sometimes be found in the blood of patients with neurodegeneration. Creatinine kinase is not specific for neurodegeneration and may also be an indicator of some other medical condition. Creatinine kinase is produced when muscle breaks down.
An MRI (magnetic resonance imaging) scan - radio waves and a powerful magnetic field produce detailed images of the brain and spinal cord on a monitor.
An EMG (electromyography) - needles are used to measure the electrical activity in the patient's muscles. A fine wire electrode is inserted into the muscles that the doctor wants to study - usually muscles from each limb and the bulbar (throat). An instrument records the electrical activity or the muscle while it is resting and contracting. Most patients find this test mildly uncomfortable. Muscles which have lost their nerve supply can be identified because their electrical activity is different from healthy muscle. The EMG may appear as abnormal even if that particular muscle is not yet affected.
A nerve conduction test - measures how fast the nerves can conduct an electrical impulse. Electrodes are attached to the skin above the nerve or muscle that is being studied. A small electric shock is passed through the nerve to measure the strength and velocity of the nerve signals.
TMS (transcranial magnetic stimulation) - the activity of the upper motor neurons is measured using a specially designed magnetic coil. This procedure may be carried out at the same time as a nerve conduction test.
Spinal tap (lumbar puncture) - the aim here is to analyze the cerebrospinal fluid (CSF); the fluid that surrounds the brain and spinal cord. Patients lie on their side with knees drawn up to the chest. A local anesthetic is injected into the area where the spinal tap occurs. A needle is then inserted into the spinal canal and some fluid is collected.
Muscle biopsy - if the doctor thinks the patient may have a muscle disease, a muscle biopsy may be performed. A small portion of muscle is removed. The patient receives a local anesthetic beforehand. The muscle sample is sent to the Laboratory for analysis.
As there is no way of reversing the progression of neurodegeneration, treatments focus on making the patient more independent and comfortable, as well as slowing down the progression. In most countries, when a patient is diagnosed they will be introduced to a team of Healthcare professionals - a multidisciplinary team - who will be actively involved in their care.
This only drug specifically targeted for neurodegeneration patients is riluzole (Rilutek®). Riluzole appears to lower the amount of glutamate in the body, resulting in slower progression of the disease. Not only does riluzole lengthen a patient's Lifespan, it also delays the onset of ventilator-dependence or tracheotomy in selected patients. Side effects include nausea, vomiting, weakness, tachycardia, dizziness, and headaches.
Other medicines may help with symptoms. Muscle relaxants such as baclofen, Zanaflex®, and the benzodiazepines may reduce spasticity. Botulinum toxin may be used to treat jaw spasms or drooling. Excessive saliva can be treated with amitriptyline, Robinul®, and Sal-Tropine™ or by botulinum injections into the salivary glands. Combinations of dextromethorphan and quinidine have been shown to reduce pseudobulbar affect. Anticonvulsants and nonsteroidal anti-inflammatory drugs may help relieve pain, and antidepressants may be helpful in treating depression. Panic attacks can be treated with benzodiazepines. Some individuals may eventually require stronger medicines such as morphine to cope with musculoskeletal abnormalities or pain, and opiates are used to provide comfort care in terminal stages of the disease.
Physical therapy, occupational therapy, and rehabilitation may help to improve posture, prevent joint immobility, and slow muscle weakness and atrophy. Stretching and strengthening exercises may help reduce spasticity, increase range of motion, and keep circulations flowing. Some individuals require additional therapy for speech, chewing, and swallowing difficulties. Applying heat may relieve muscle pain. Assistive devices such as supports or braces, orthotics, speech synthesizers, and wheelchairs may help some people retain independence.
Proper nutrition and a balanced diet are essential to maintaining weight and strength. People who cannot chew or swallow may require insertion of a feeding tube. In ALS, insertion of a percutaneous gastronomy tube (to help with feeding) is frequently carried out even before it is needed, when the individual is strong enough to undergo this minor surgery. Non-invasive ventilation at night can prevent apnea in sleep, and some individuals may also require assisted ventilation due to muscle weakness in the neck, throat, and chest during daytime.
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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