Multiple Sclerosis: A Disorder of the Nervous System
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Multiple Sclerosis: A Disorder of the Nervous System Document Transcript

  • 1. Multiple Sclerosis, 1 Multiple Sclerosis: A Disorder of the Nervous System Lisa Skiver and Haily Vora Topics in Medicine and Biology Mr. Wilson Kwok Summer Ventures July, 2006
  • 2. Multiple Sclerosis, 2 Abstract Multiple Sclerosis (MS) is a disorder of the nervous system. It is characterized by the gradual decay of the myelin sheath and axons of the nerves. There are two main types of MS: Relapsing-remitting MS and Chronic-progressive MS. What factors actually cause multiple sclerosis are still unknown, but there are many theories derived from extended research by scientists and doctors. Two of the most supported beliefs among experts for the cause of MS are genetic factors and infectious agents. People who are susceptible to MS usually start developing symptoms after the age of 20 and women are twice as likely to acquire the disorder. Even though the causes are unknown, the accepted theory is that the body’s damaged immune system is unable to differentiate between a virus and its own myelin, causing autoimmunity, or a self- attack. To diagnose MS, a brain MRI scan is usually used. The symptoms of multiple sclerosis differ from person to person and day to day. Weakness, fatigue, pain and bladder difficulties are just a few symptoms among many. Though there is no cure for multiple sclerosis, most cases can be treated and cared for with a number of drugs currently on the market. Research is continuously being done to try and solve the mystery of multiple sclerosis.
  • 3. Multiple Sclerosis, 3 Introduction Multiple Sclerosis is the most common cause of neurological debilitation in young people around the world. It affects approximately 500,000 people in the United States and occurs in about 0.1% of all people worldwide. Affecting every 3 in 10,000 people, Northern Europe and the Northern US have the highest diagnosis rate. No two people have the exact same form of MS and the course of each patient’s disorder is as unique as the number of hairs on their head. The advance of the disease, within an individual and a whole population, largely differ in their timing, severity and location. So, where does this decaying, degenerative disorder emerge from? The Nervous System Multiple Sclerosis originates in the central nervous system, and to fully understand this disorder, one must be familiar with the system. The body’s nerves do not form one single system, but several which are interrelated. Some of these are physically separate; others are different in function only. The brain and spinal cord make up the Central Nervous System (CNS) and the Peripheral Nervous System (PNS) is responsible for the body functions which are not under conscious control such as the heartbeat or the digestive system. The CNS represents the largest part of the nervous system. Working with the PNS has the essential role in the control of behavior and information processing. The CNS stems from the neural plate which forms the neural tube during embryonic development. This tube will eventually branch off into two major subdivisions, the spinal cord and the brain. These two vital parts of the body form what is known as the CNS. Its overall function is to collect information about the external conditions in relation to the body's internal state, to analyze this data, and to trigger the appropriate response to satisfy certain needs.
  • 4. Multiple Sclerosis, 4 Within the CNS, the brain and spinal cord play a vital role in body communication. The spinal cord is the crucial link between the whole body and the brain. It emerges from the base of the skull and continues down the back for 42-45 cm through the vertebral column. There are 31 pairs of spinal nerves, part of the PNS, which stem from the spinal cord. Each one of these nerves contains a dorsal root and a ventral root. The dorsal roots contain the neurons that carry messages to the CNS from numerous sensory neurons. The ventral roots contain the axons of motor neurons. There are also interneurons within the spinal cord. Besides carrying signals to and from the brain, the spinal cord also regulates reflexes, the simplest response to a stimulus. Most reflexes never reach the brain due to the immediate response of the sensory and motor neurons in the spinal cord. Even though the spinal cord does all the work, there would be no nervous system without the brain. The brain is divided into three main sections: the forebrain, the midbrain, and the hindbrain. The forebrain is the largest and most complex part of the brain and contains the cerebrum. The cerebrum contains the information that makes a person; intelligence, memory, personality, emotion and speech. The outer layer of the cerebrum is called the cortex. It collects information coming in from the spinal cord from the five senses. The brain then directs this data to other parts of the nervous system for more processing. The midbrain is located underneath the middle of the forebrain. It acts as an efficient organizer for all the messages going in and out of the brain through the spinal cord. The hindbrain sits underneath the back of the cerebrum and contains the cerebellum, pons and medulla. The cerebellum is responsible for balance, movement and coordination. Together with the midbrain, the pons and medulla are often called the brainstream. They take in, send out and coordinate all of the brain’s messages.
  • 5. Multiple Sclerosis, 5 The messages the spinal cord carries from the body to the brain are analyzed and interpreted and response messages are sent throughout the rest of the body. The cells that carry these messages are called neurons. The messages they send take the form of electrical signals, also known as impulses, which only travel in one direction. Neurons can be further classified into three different types: sensory receptor neurons, motor neurons, and interneurons. Sensory receptor neurons carry impulses from the sensory organs to the brain and spinal cord. Receptors sense changes, both internal and external, and send the information to the CNS through electric signals. They are responsible for converting external stimuli to internal motor mechanisms and some forms of involuntary behavior. Sensory neurons are commonly located in the spinal cord and carry sensations such as feelings, impressions and awareness throughout the body. Figure 1. Sensory Neuron - Picture adapted from Motor neurons, also known as efferent neurons, carry messages to muscles and glands. They originate in the spinal cord or brain stem and promote muscle contraction. With enough stimulation, the motor neuron will release a flood of neurotransmitters that will bind to receptors on muscle fiber and initiate a response. The response of a muscle fiber to a neurotransmitter is contractile and inhibition of muscle contraction can only occur when the motor neuron itself is inhibited.
  • 6. Multiple Sclerosis, 6 Figure 2. Motor Neuron – picture adapted from Interneurons connect sensory neurons to motor neurons and carry impulses between the two. They are found only in the CNS and the brain, alone, contains over 100 billion interneurons. They only communicate to other neurons and are sometimes called relay neurons. Interneurons can be used as inhibitors which theoretically help block out boring or irrelevant input and help focus attention on relevant sensory input. Figure 3. Interneuron – picture adapted from
  • 7. Multiple Sclerosis, 7 All neurons have a cell body, dendrites, and one axon. The cell body is the largest part, containing the nucleus, most of the cytoplasm and metabolic cell activity. It generates ATP and synthesizes proteins. The dendrites are short branch extensions that spread out from the cell body. They receive stimulus and carry impulses from the environment toward the cell body. The axon of a neuron is a long fiber that carries impulses away from the cell body. The axon ends with an array of swellings called axon terminals. Neurons can have hundreds of dendrites, but usually only one axon. These axons are covered with a lipid layer known as a myelin sheath. Myelin can greatly increase the speed at which an impulse travels along an axon. It is made of Schwann cells that form an insulated wrap around the axon. Along the axon, there are gaps between the myelin sheaths called the Nodes of Ranvier. As an impulse moves down an axon, it jumps between the sheaths instead of traveling straight down the membrane. This jumping from node to node decreases the time it takes for an impulse to travel. However, sometimes these crucial myelin sheaths can be destroyed and nerve function becomes impaired, thus, causing Multiple Sclerosis. What is it? So what exactly is MS? The principal characteristic of the disorder is the destruction of the myelin. The end result of this process is multiple patches of hard, scarred tissue called plaques. This is called demyelination. Another important feature in the disease is the destruction of axons, which is now considered to be a major factor in the permanent disability associated with MS.
  • 8. Multiple Sclerosis, 8 Figure 4. Neuron and Myelin – picture adapted from Types of MS Relapsing-remitting multiple sclerosis is the most common type of MS and usually occurs in young people. The most common characteristic of relapsing-remitting MS is the attack or relapse. It is an attack of MS symptoms such as facial pain or bladder instability that lasts at least 24 hours and usually for a few days. Most of these attacks are fairly mild and are followed by a period of remission. The symptoms improve or disappear for about six to eight weeks. To be considered a remission, there must be 30 days between relapse sessions. Remissions are almost always followed by a flare-up. Some relapsing-remitting MS patients can go years without experiencing any progression, although by 25 years, most patients have converted to a progressive stage. Chronic-progressive multiple sclerosis is a type of MS where the patient has no periods of remission and their symptoms continue to worsen slowly. Most patients who develop MS after the age of 45 are afflicted with the chronic-progressive type of MS without first developing relapsing-remitting MS. Chronic-progressive MS has a wide spectrum of severity and is categorized into three groups: Primary-Progressive MS (PPMS), Secondary-Progressive MS (SPMS), Progressive-Relapsing MS (PRMS). PPMS progresses gradually with no remission but can occasionally level off and even have minor improvement. SPMS occurs after the relapsing- remitting phase in about half of MS patients within 10 years and almost all after 25 years. It’s an evolving course of nerve and muscle decay with intermittent flare-ups, remissions and plateaus. PRMS is progressive from the beginning with intense symptoms and continued disintegration between relapses. It is the least common type of MS, occurring in only 5% of patients. Causes
  • 9. Multiple Sclerosis, 9 Despite the great progress that has been made in trying to find a cute for MS, the cause for this degenerative disorder is still unknown. Genetics most probably play a role in MS, but no single gene is responsible for the disorder. Currently, the most popular theory is that the disease occurs in people with a genetic susceptibility who were exposed to some environmental attack (a virus or a toxin) that disrupts the blood-brain barrier. Immune factors gather in the nerve cells and cause inflammation and an autoimmune attack on myelin and axons. Still, some experts believe that MS may prove not just be a single disorder, but may represent several diseases with several different causes. Genetic factors may make a person more vulnerable to MS, but the risk for someone inheriting the disorder is less than 5%. Close relatives of a patient with MS are more likely to develop it themselves. Some researchers believe that there is more than one gene that increases susceptibility. Other scientists believe that MS develops because a person is born with a genetically lower tolerance to some environmental agents, and instead of a normal response, the exposure triggers an autoimmune response. However, as technology improves, techniques are being developed to identify genes that are most likely responsible for MS. Infectious agents, viruses in particular, are most likely the cause of an autoimmune response in people genetically susceptible to MS. Much research and experimentation has been done to support this belief: • Geographical Distribution – MS is a disease of temperate climates. The number of MS cases increases the further one gets from the equator in either direction. Multiple Sclerosis is very rare in traditional culture, but it increases in industrialized Western nations.
  • 10. Multiple Sclerosis, 10 • MS Clusters – Four separate clusters of MS outbreaks occurred between 1943 and 1989 in the Faroe Islands (located between Iceland and Scandinavia). During WWII, the area was occupied by British troops and the number of patients with MS increased each year for 20 years, following the war. Some researchers think that the troops could have brought the disease causing agent with them. • Sexually Transmitted Infection – The disease clusters in the Faroe Islands could be related to high sexual activity between the troops and the native women. High diagnosis rates are found in countries with a high degree of sexual permissiveness. • Viral Similarity – Some viruses are extremely similar to myelin protein and could therefore confuse the immune system, causing the T-cells to attack their own protein instead of the virus. • HIV-6 – Herpesvirus 6 is known to cause encephalitis, or brain inflammation in patients with damaged immune systems. Many studies have shown that some MS patients have higher rates of HHV-6 infection than normal. Some scientists and doctors believe this may be important to discovering the cause of MS, while others argue that nearly everyone harbors this virus and there is not a strong enough relationship between MS and HHV-6. • Chlamydia Pneumoniae – This bacterium has been associated with persistent inflamed small vessels. A few studies have shown that patients with MS have a significantly higher rate of previous Chlamydia infection. Many experts disagree, but it is possible that the infection, which widely spreads inflammation, could play an early role in the course of MS.
  • 11. Multiple Sclerosis, 11 • Epstein-Barr virus (EBV) – Almost all people with MS have evidence of EBV infection, the cause of mononucleosis. However, EBV is very common in people who will never develop mono. • Other viruses have been explored such as the measles virus, adenovirus, polyomavirus, and the retroviruses (HIV, HTLV-I, HTLV-II). Figure 5. Environmental Theory – picture adapted from Who is most likely to get MS? Women are twice as likely to get MS as men. Most people start developing symptoms between the ages of 20 and 40. People from Northern Europe, the United States and Canada are more likely to develop MS than Asian people, Eskimos and American Indians. It is an inherited disease in the sense that a child or sibling of someone with MS is about 10 times more likely to get MS than someone in the population at large. Process
  • 12. Multiple Sclerosis, 12 Although the causes are unknown, research has led scientists to better understand what exactly happens within an MS patient’s body. The common and accepted theory for the development of MS is that a damaged immune system is unable to differentiate a virus protein and the body’s own myelin. It generates antibodies to attack and basically becomes allergic to itself, causing autoimmunity. In the case of MS, the body attacks the myelin tissues. In MS, an unknown trigger activates helper T-cells whose antigen specific receptors recognize central nervous system myelin as an antigen. Once triggered, the activated T-cells reproduce clones that have the same myelin-specific activation. All of the activated T-cells then release cytokines and adhesion molecules that enable the T-cells to adhere to and cross over the blood-brain barrier, which normally prohibits the flow of substances into the brain. The greatly weakened barrier becomes easily permeable, allowing additional immune system cells, such as B-cells and cytotoxic T-cells to cross over. Once through the barrier, B-cells produce antibodies which bind to the oligodendracytes (the cells of the CNS which create myelin) and the myelin itself. Associated macrophages proceed to destroy the myelin and may also damage the oligodendracytes. As the body starts to attack itself, the myelin sheath is destroyed, marking the climax of multiple sclerosis. The nodes in the sheath house channels for sodium ions that boost the electrical charge required to pass nerve signals. As the myelin insulation is being destroyed, signals transmitted from nerve to nerve throughout the CNS are disrupted. The destruction of axons is now well established as a major feature of MS. Research shows that axons are severed early on in the process and as the disease progresses, the exposed axons decay even further. This is most likely the major reason for MS irreversibility.
  • 13. Multiple Sclerosis, 13 The body does seem to have some sort of defense against MS though. Studies show that the body increases the density of sodium ions that carry electric charges. By increasing these ions, the nerves can continue to communicate despite the lack of myelin. It has also been shown that the body can retain some remyelinate, used to restore the insulating myelin. These processes are most likely responsible for the remission that some MS patients experience. However, the disease is too powerful and eventually outpaces the body’s attempt to correct itself. Diagnosis The diagnosis of MS is based on the presence of central nervous system (CNS) lesions that occur in different parts of the CNS at least three months apart, with no better explanation for the disease process. No single test is totally reliable in identifying MS and other conditions of the CNS can occur that are very similar to the disease. CNS infections such as Lyme disease, syphilis, human immunodeficiency virus infection and human T-lymphotrophic virus type I mimic MS. Also, CNS inflammatory conditions such as sarcoidosis and systemic lupus erythematosus and genetic disorders such as leukodystrophy, hereditary myelopathy and mitochondrial disease can be very similar in nature to MS. The International Panel on MS Diagnosis has made several changes to the older diagnostic criteria in 2001 referring to the newer criteria as the McDonald criteria. They have incorporated specific MRI (magnetic resonance imaging) findings into the diagnostic scheme. The major advantage of the proposed criteria is that an early diagnosis of MS can be made if an MRI scan performed three months after a clinically isolated attack demonstrates formation of a new lesion. The proposed diagnostic criteria also define MRI lesion characteristics that increase the likelihood of MS. This includes • number of lesions: nine or more
  • 14. Multiple Sclerosis, 14 • location of lesions position abutting the ventricles: juxtacortical, infratentorial, or spinal position • lesion enhancement with the use of contrast medium. The MRI lesion characteristics that suggest multiple sclerosis consist of brain lesions and spinal cord lesions. These characteristics are shown in Table 1. Table adapted by TABLE 1 MRI Lesion Characteristics Suggestive of Multiple Sclerosis Brain lesions High signal on T -weighted and FLAIR MRI sequences (more than nine lesions) 2 When actively inflamed, often enhanced with gadolinium contrast Position abutting ventricles (often perpendicular) Juxtacortical position (gray-white junction) Involvement of brainstem, cerebellum, or corpus callosum Spinal cord lesions One or two vertebral segments in length Incomplete cross-sectional involvement (dorsolateral common) Less likely to enhance with gadolinium contrast No cord swelling Better seen with STIR MRI sequences MRI = magnetic resonance imaging; FLAIR = fluid attenuation inversion recovery; STIR = short tau inversion recovery. Table 1. MRI Lesion Characteristics Suggestive of MS – table adapted from Types of testing A brain MRI scan is the most useful test for confirming the diagnosis of MS. MRI is a test that produces very clear pictures of the human body without the use of X-rays. It uses a large magnet, radio waves and a computer to produce these images. Disease-related changes in the brain or spinal cord are detected by MRI in more than 90% of people suspected of having MS. MRI scanning is useful for detecting structural pathology in regions that can be difficult to see through computer images, such as the posterior fossa, craniocervical junction, and cervical cord.
  • 15. Multiple Sclerosis, 15 Figures 6 and 7. MS Brains – pictures adapted from In the image above to the right, the arrows show the multiple high-signal white lesions, showing suggestive characteristics of MS. In the image to the left, a fluid attenuation inversion recovery (FLAIR) image of a slice of the brain is shown. A lumbar puncture, or a spinal tap, where a sample of cerebrospinal fluid is taken by inserting a needle between two vertebrae of the spine can be performed to diagnose MS. A spinal tap that reveals a large number of immunoglobulins as well as oligoclonal bands or certain proteins that are the breakdown products of myelin is suggestive of MS. These findings indicate an abnormal autoimmune response within the brain and spinal cord, meaning that the body is attacking itself. Over 90% of people with MS have oligoclonal bands in their CSF. While increased immunoglobulin in the CSF and oligoclonal bands are seen in many other brain and spinal cord conditions, their presence is often useful in helping to establish a diagnosis of MS. Sensory evoked potential testing may also be used in finding MS in the human body. Evoked potential tests measure electrical activity in certain areas of the brain in response to stimulation of certain groups of nerves. These tests are often used to assist in the diagnosis of MS because they can indicate problems along the pathways of certain nerves that are too small to be noticed or found on a physician’s exam. Direst results of the disease are problems along the
  • 16. Multiple Sclerosis, 16 nerve pathways. The demyelination causes the nerve impulses to be slowed or stopped altogether. The three main types of evoked potential tests are visual, brainstem auditory, and sensory. In visual evoked potentials, or VEP, the patient looks at a screen on which an alternating checkerboard pattern is displayed. In brainstem auditory evoked potentials, or BAEP, the patient hears a series of clicks in each ear. And, in sensory evoked potentials, or SEP, short electrical impulses are sent to a patient’s arm or leg. Symptoms The symptoms of MS obviously vary from person to person and even from day to day. There are many common symptoms, though, to indicate a potential case of MS. These are the common possible symptoms of MS: • Weakness • Pain • Bladder and Bowel Dysfunction • Fatigue • Cognitive dysfunction • Difficulty in walking (gait) • Dizziness and Vertigo • Numbness • Sexual Dysfunction • Spasticity • Depression and other emotional changes • Vision Problems Table 2. MS Symptoms – table adapted from When caused by MS, weakness is a result of damaged nerve impulse flow, preventing instructions from reaching the extremities. This type of weakness does not result from any type of loss in muscle strength. About 75% of MS patients experience bladder difficulties at some time. The most common symptoms are frequency (the urge to urinate often) and urgency (the urge to urinate immediately and the inability to hold the urine once the urge is felt).
  • 17. Multiple Sclerosis, 17 For a patient with MS, having bowel dysfunctions means having constipation. Constipation is more apparent in those with MS than the general population and can be regulated when Timing, fluid intake, diet and physical activity are taken into consideration. Approximately 50% of people with MS will develop some degree of cognitive dysfunction, affecting the ability to think, reason, concentrate or remember. The memory is the cognitive function most likely to be affected. Other cognitive functions frequently affected in MS include speed of information processing, executive functions (planning and prioritizing), visuospatial functions (impairment in visual perception and constructional abilities), abstract reasoning and problem-solving, and attention and concentration. One of the reasons MS may affect cognitive function for several reasons is because MS damages both myelin and the nerve cells within the brain, thereby compromising a variety of functions handled by the brain. Dizziness is a common symptom of MS. Those with MS may feel off balance or lightheaded. Much less often, they have the sensation that they or their surroundings are spinning —a condition known as vertigo. These symptoms are due to lesions, or damaged areas, in the complex pathways that coordinate visual, spatial, and other input to the brain needed to produce and maintain equilibrium. Sexual problems are often experienced by people with MS. Sexual arousal begins in the central nervous system, as the brain sends messages to the sexual organs along nerves running through the spinal cord. If MS damages these nerve pathways, sexual response—including arousal and orgasm—can be directly affected. Sexual problems also stem from MS symptoms such as fatigue or spasticity, as well as from psychological factors relating to self-esteem and mood changes. In both men and women, symptoms of sexual dysfunction include difficulty achieving orgasm and loss of libido.
  • 18. Multiple Sclerosis, 18 Depression may be the result of difficult life situations or stresses. It is easy to understand how a diagnosis of multiple sclerosis, a chronic condition with the potential for progressing to permanent disability, can bring on depression. It may also be a result of the MS disease process itself, since MS damages the myelin and nerve fibers deep within the brain. If MS damages areas of the brain that are involved in emotional expression and control, a variety of behavioral changes can result, including depression. Also, some of the emotional changes observed in MS include major depressive episodes as well as less severe depressive symptoms, grieving for losses related to the disease, stress and reactions to stressful situations, generalized distress and anxiety and emotional lability or mood swings. Another symptom a person with MS might experience is pain. When experiencing acute pain, one has cases of trigeminal neuralgia, Lhermitte's sign and burning or aching around the body. In trigeminal neuralgia is a stabbing pain in the face which is neuropathic, or caused by damage to the trigeminal nerve. It can occur as an initial symptom of MS. Lhermitte's sign is a brief, stabbing, electric-shock-like sensation that runs from the back of the head down the spine, brought on by bending the neck forward. Burning and aching around the body are all neurological symptoms. The technical name for them is dysesthesias. Acute symptoms of pain are milder than chronic symptoms. Chronic pain includes burning, aching or prickling, pain of spasticity and back and other musculoskeletal pain. Burning, aching or prickling can be a chronic form of the acute symptoms. Pain of spasticity has two categories. Muscle spasms or cramps, called flexor spasms, may occur. Tightness and aching in joints is another type of spasticity. Fatigue is one of the most common symptoms of MS, occurring in about 80% of people. It is a debilitating kind of overall weariness, which is not predictable and unrelated to your activity level. Increase in body temperature will temporarily worsen fatigue. It can
  • 19. Multiple Sclerosis, 19 significantly interfere with a person's ability to function at home and at work, and may be the most prominent symptom in a person who otherwise has minimal activity limitations. MS fatigue is unique in that it: • Generally occurs on a daily basis • May occur early in the morning, even after a restful night's sleep • Tends to worsen as the day progresses • Tends to be aggravated by heat and humidity • Comes on more easily and suddenly • Is generally more severe than normal fatigue • Is more likely to interfere with daily responsibilities Table 2. MS fatigue characteristics - Table adapted by Fatigue.asp Problems with gait (difficulty in walking) are among the most common mobility limitations in MS. Gait problems are usually related to several factors including weakness, spasticity, loss of balance, sensory deficit and fatigue. Numbness of the face, body, or extremities (arms and legs) is another one of the most common symptoms of MS, and is many times the first symptom experienced by those eventually diagnosed with MS. The numbness may be mild or so severe that it interferes with the ability to use the affected body part. Numb hands may prevent writing, dressing, or holding objects safely. Many people with MS have problems with spasticity, a condition that primarily affects the lower limbs. Spasticity refers to feelings of stiffness and a wide range of involuntary muscle spasms. It may be as mild as the feeling of tightness of muscles or may be so severe as to produce painful, uncontrollable spasms of extreme levels, usually of the legs. Spasticity may also produce feelings of pain or tightness in and around joints, and can cause low back pain. Two types of severe MS-related spasticity are flexor spasticity and extensor spasticity. Flexor spasticity, involving the hamstrings and hip flexors, refers to bent hips and knees that are difficult to straighten. Extensor spasticity, on the other hang, involves the quadriceps and
  • 20. Multiple Sclerosis, 20 adductors. Here, the hips and knees remain straight with the legs very close together or crossed over at the ankles. Vision problems can also be a symptom of MS but very rarely does it result in vision loss. The problems with vision include optic neuritis, uncontrolled eye movement and double vision. Optic neuritis is an inflammation of the optic nerve, the nerve that transmits light and visual images from the retina to the brain. The condition is also known as retrobulbar neuritis because the nerve is located behind the globe of the eye. Optic neuritis is generally experienced as an acute blurring, graying, or loss of vision, almost always in one eye. Nystagmus, or uncontrolled horizontal or vertical eye movements, is another common symptom. It may be mild, only occurring when the person looks to the side or it may be severe enough to impair vision. Diplopia, or double vision, happens when muscles controlling eye movement are not perfectly coordinated due to weakness in one or both pairs of muscles. When the images are not properly synched, a false double image occurs. Double vision may increase with fatigue or overuse of the eyes. Patching one eye can be done until regular eyesight returns. Treatment A cure has not been found for multiple sclerosis. Diagnosed early, most cases of MS can be cared for. Studies indicate that early treatment delays disability, presumably by decreasing the injury to the nervous system caused by the disease. Generally, treatment of the disease falls into two categories: treatments that address symptom management, and treatments that change the course of the disease by modifying the number and severity of attacks and the progression of disability. Five different products have been approved by the FDA as disease modifying treatments for MS since 1993. These included three interferon-beta products (Betaseron®, Avonex®, and Rebif®) and two unrelated products (Copaxone®, Novantrone®).
  • 21. Multiple Sclerosis, 21 Betaseron® was the first beta interferon to be approved by the FDA and marketed in the United States. The product shuts down the inflammation of MS lesions through various mechanisms including repairing the blood brain barrier and reducing the inflammatory process in the lesions. Betaseron® decreases relapse rate, increases time between attacks, decreases the severity of attacks, while decreasing the amount of accumulated lesions seen on MRI. Betaseron® is to be taken every other day through an injection under the skin. This product provides the highest dose of interferon-beta available for treatment of MS. Marketed by Berlex Laboratories, Inc. Avonex® is known to slow the rate of progression of disability in relapsing-remitting MS. It has been demonstrated to decrease the relapse rate and the amount of accumulated damage seen on MRI, but to a lesser extent than other available agents. Avonex® is given every week through an intramuscular injection. Avonex® treats the relapsing-remitting type of MS. Marketed by Biogen, Inc. Rebif® is identical in chemical structure to Avonex®. The difference is that Rebif® is given just under the skin rather than in the muscle in higher and more frequent doses. Rebif is effective in reducing the number and severity of relapses, delaying the progression of disability, and reducing the number of new and accumulated lesions seen on MRI. It is approved for use in relapsing-remitting MS. Marketed by Serono, Inc. Copaxone® is different from beta interferon in chemical structure and mechanisms of action. It consists of a group of amino acids that looks something like myelin itself. It acts by suppressing the immune system's attack on myelin and possibly other mechanisms. It decreases the frequency and severity of attacks to the same extent as Betaseron and Rebif, but with slightly
  • 22. Multiple Sclerosis, 22 less effect on MRI lesions. Copaxone® is taken daily through an injection just underneath the skin and is used for relapsing-remitting MS. Novantrone® another chemotherapy agent that slows disease progression in MS and lessens the number of relapses through its ability to suppress the activity of T cells and B cells. These white blood cells attack the myelin that protects nerve cells, and by doing so causes the scarring associated with MS. It is approved for MS that is getting worse and worse including secondary progressive and relapsing-remitting forms of the disease. Novantrone is typically administered through an injection into the vein once every three months for two years. Marketed by Immunex Corporation. For acute exacerbations, steroids have been reported to shorten the duration of acute attacks by lessening the swelling and inflammation in MS lesions. However they do not alter the frequency of exacerbations or the progression of the MS, and long term use should be avoided except in selected patients. Conclusion Though multiple sclerosis is not a fatal disease, it has been known to shorten the lifespan of those who have been diagnosed with MS by about six years. Understanding MS and its origins are often difficult to understand because of the complexity of the part of our body we call the nervous system. Scientists and medical doctors everywhere are trying to understand the nervous system and therefore understand the diseases that come from it. Doing this takes them one step closer to finding a cure. Those with MS can lead their daily lives with little complication, but they know that they will be living with the disease forever. To find a cure would be a dream come true. With the technology of today, this dream is just around the corner.
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