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AMYOTROPHIC LATERAL SCLEROSIS CAUSES |
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The symptoms of Amyotrophic Lateral Sclerosis are caused by the
death of motor neurons in the spinal cord and brain. Normally, these
neurons convey electrical messages from the brain to the muscles to
stimulate movement in the arms, legs, trunk, neck, and head. As
motor neurons die, the muscles cannot be moved as effectively, and
weakness results. In addition, lack of stimulation leads to muscle
wasting, or loss of bulk. Involvement of the upper motor neurons
causes spasms and increased tone in the limbs, and abnormal reflexes.
Involvement of the lower motor neurons causes muscle wasting and
twitching (fasciculations). Although many causes of motor neuron degeneration have been suggested for Amyotrophic Lateral Sclerosis, none has yet been proven responsible. Results of recent research have implicated toxic molecular fragments known as free radicals. Some evidence suggests that a cascade of events leads to excess free radical production inside motor neurons, leading to their death. Why free radicals should be produced in excess amounts is unclear, as is whether this excess is the cause or the effect of other degenerative processes. Additional agents within this toxic cascade may include excessive levels of a neurotransmitter known as glutamate, which may overstimulate motor neurons, thereby increasing free-radical production, and a faulty detoxification enzyme known as SOD-1, for superoxide dismutase type 1. The actual pathway of destruction is not known, however, nor is the trigger for the rapid degeneration that marks Amyotrophic Lateral Sclerosis. Further research may show that other pathways are involved, perhaps ones even more important than this one. Autoimmune factors or premature aging may play some role, as could viral agents or environmental toxins. Two major forms of Amyotrophic Lateral Sclerosis are known: familial and sporadic. Familial Amyotrophic Lateral Sclerosis accounts for about 10% of all Amyotrophic Lateral Sclerosis cases. As the name suggests, familial Amyotrophic Lateral Sclerosis is believed to be caused by the inheritance of one or more faulty genes. About 15% of families with this type of Amyotrophic Lateral Sclerosis have mutations in the gene for SOD-1. SOD-1 gene defects are dominant, meaning only one gene copy is needed to develop the disease. Therefore, a parent with the faulty gene has a 50% chance of passing the gene along to a child. Sporadic Amyotrophic Lateral Sclerosis has no known cause. While many environmental toxins have been suggested as causes, to date no research has confirmed any of the candidates investigated, including aluminum and metal dental fillings. As research progresses, it is likely that many cases of sporadic Amyotrophic Lateral Sclerosis will be shown to have a genetic basis as well. A third type, called Western Pacific Amyotrophic Lateral Sclerosis, occurs in Guam and other Pacific islands. This form combines symptoms of both Amyotrophic Lateral Sclerosis and Parkinson's disease. Symptoms The earliest sign of Amyotrophic Lateral Sclerosis is most often weakness in the arms or legs, usually more pronounced on one side than the other at first. Loss of function is usually more rapid in the legs among people with familial Amyotrophic Lateral Sclerosis and in the arms among those with sporadic Amyotrophic Lateral Sclerosis. Leg weakness may first become apparent by an increased frequency of stumbling on uneven pavement, or an unexplained difficulty climbing stairs. Arm weakness may lead to difficulty grasping and holding a cup, for instance, or loss of dexterity in the fingers. Less often, the earliest sign of Amyotrophic Lateral Sclerosis is weakness in the bulbar muscles, those muscles in the mouth and throat that control chewing, swallowing, and speaking. A person with bulbar weakness may become hoarse or tired after speaking at length, or speech may become slurred. In addition to weakness, the other cardinal signs of Amyotrophic Lateral Sclerosis are muscle wasting and persistent twitching (fasciculation). These are usually seen after weakness becomes obvious. Fasciculation is quite common in people without the disease, and is virtually never the first sign of Amyotrophic Lateral Sclerosis. While initial weakness may be limited to one region, Amyotrophic Lateral Sclerosis almost always progresses rapidly to involve virtually all the voluntary muscle groups in the body. Later symptoms include loss of the ability to walk, to use the arms and hands, to speak clearly or at all, to swallow, and to hold the head up. Weakness of the respiratory muscles makes breathing and coughing difficult, and poor swallowing control increases the likelihood of inhalation of food or saliva (aspiration). Aspiration increases the likelihood of lung infection, which is often the cause of death. With a ventilator and scrupulous bronchial hygiene, a person with Amyotrophic Lateral Sclerosis may live much longer than the average, although weakness and wasting will continue to erode any remaining functional abilities. Most people with Amyotrophic Lateral Sclerosis continue to retain function of the extraocular muscles that move the eyes, allowing some communication to take place with simple blinks or through use of a computer-assisted device. |
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| AMYOTROPHIC LATERAL SCLEROSIS RELATED ITEMS | ||
