In multiple sclerosis (MS), the immune system attacks the protective covering of the nerves, leading to impaired sensory and motor nerve function, and in most cases some degree of disability Figure 01. The myelin sheath is a protective covering around a portion of nerve cells that allows the cells to transmit impulses quickly and effectively. In MS, the myelin sheath is damaged, causing varying symptoms that include increased difficulty moving and progressive weakness.
MS follows four basic courses: relapsing-remitting, secondary progressive, primary progressive, and progressive-relapsing. During the first course, which is called relapsing-remitting MS, your symptoms will come and go. On average, a person will have a relapse every two years. Approximately 15% of all patients will only have a single attack of MS, and then never have symptoms again. In addition, some people have MS that will follow a relapsing-remitting course, but their symptoms will not progress. In fact, symptoms do not progress during the first 10 years of diagnosis in 50% of patients with relapsing-remitting disease.
The second course, which is called secondary progressive MS, also follows a pattern of relapse and remission, but symptoms get worse with each relapse. Thirty to fifty percent of patients with relapsing-remitting MS will eventually develop secondary progressive MS.
Fewer than 15% of MS patients will develop the third form, which is called primary progressive MS. In this form, symptoms get worse over time, and there is no distinct relapse-remission pattern.This form of MS is most common in people whose symptoms begin after the age of 40.
The fourth and most rare course of disease is called progressive-relapsing MS. In this form, the disease steadily worsens with distinct relapse periods. Approximately 5% of MS patients are diagnosed with this form of the disease.
Figure 01. Normal Nerve Cell with Myelin Sheath
Multiple sclerosis is an autoimmune disease, meaning that it occurs when the body’s immune system attacks itself. In MS, white blood cells known as T-cells launch an attack against the myelin sheath. This causes other immune-system cells to flood the area, leading to inflammation, swelling, and ultimately damage to the myelin sheath. The blood-brain barrier, which normally prevents drugs and other substances from traveling from the blood to the brain, also becomes much more permeable, leading to swelling and other problems. The myelin develops scars, which makes it more difficult for nerve impulses to travel along the axon of the nerve cells.
Environmental and hereditary factors are known to play a role in MS. The geographic prevalence of MS decreases nearer the equator, suggesting that some type of environmental exposure plays a role in a person’s likelihood of developing the disease. Genetics are also involved in MS, as shown by the fact that people with a close relative with MS have an increased risk of developing the disease. Some ethnic groups have a higher risk of MS than others; in the US, the disease is more common among Caucasians. Several interacting genes in conjunction with environmental factors (rather than by the action of a single gene) probably cause MS.
Table 1. Symptoms of Multiple Sclerosis
Blurriness in the central visual field that affects only one eye; may be accompanied by pain upon eye movement Double vision Odd sensation in legs, arms, chest, or face, such as tingling or numbness Weakness of arms or legs Heat sensitivity (symptoms worsen, reappear upon exposure to heat such as a hot shower) Loss of dexterity Difficulty coordinating movement Difficulty controlling bowel movements or urination
Patients with MS typically experience an array of sensory and motor symptoms Table 01. The most common first symptoms are weakness or numbness in one or more limbs, blurry or double vision and other sensory disturbances, and an inability to coordinate voluntary movements (ataxia). Sometimes patients experience such mild initial symptoms that medical attention will seem to be unnecessary.
Additional sensory symptoms include tingling or other unusual sensations in the extremities, trunk, or face; feelings of weakness or heaviness in the arms or legs; visual problems; vertigo, and dizziness.
Aside from ataxia, additional motor symptoms that may occur include slurred speech, unsteady gait, tremors, and loss of coordination. Spasticity is another common symptom of MS, and is characterized by abnormally tense muscles and exaggerated tendon reflexes. People with MS also often experience pain in the affected muscles during an attack.
Most patients with MS experience fatigue, which may manifest as sleepiness, mental exhaustion, or weakness.
People with MS may lose the ability to empty their bladder completely, and may also become incontinent. Bowel incontinence may occur, but constipation is more common. While most women with MS are still able to experience orgasm, men with MS may have difficulty achieving an erection.
Symptoms of MS come and go. An "attack" of symptoms typically develops over several hours or days and lasts for a few days to a few weeks. In the relapsing-remitting course of disease, the symptoms gradually improve, and a patient may or may not be left with lasting neurological effects. A person with one of the relapsing-remitting forms of MS will, on average, have an attack or relapse every two years. About 15% of people with MS will never have a second relapse.
Symptoms of MS may worsen over time, and may be triggered by certain factors or behaviors. Numbness, for example, may begin in a specific place, and then spread outward over hours or days. Blurred vision often occurs in one eye only, starting at the center of the visual field and progressing outward over time. There may also be pain behind the eye that worsens with eye movement. Patients generally recover their vision completely after an attack of this sort.
Symptoms will worsen or return with a hot shower, exercise, fever, or other exposure to high temperature.
Hyperventilation may precipitate paroxysmal attacks, which are clusters of symptoms that may occur early in the course of MS. Paroxysmal attacks are brief recurrent episodes of tingling or other strange sensations associated with muscle contraction. These attacks may last for a moment, or as long as 30 seconds.
A person with MS may develop mild intellectual or emotional changes. The most common cognitive changes are impairment of short-term memory, difficulty paying attention or shifting attention between tasks, and slowed information processing.
Having a close relative with MS, living in the northern latitudes, and being female all increase a person’s likelihood of developing MS. Studies have demonstrated a clear association between genetics and MS risk. However, researchers believe that MS is caused by an interplay of genetic mutations rather than a single gene.
The overall risk of developing MS for the general population is less than .1%.
An identical twin of a person with MS has a 31% risk of developing the disease, while a fraternal twin’s risk is 5%; a person with a sibling with MS has a 2% to 5% risk of developing MS. A person with another close relative with MS (not a sibling or parent) has eight times the normal risk of developing MS.
MS is most prevalent among people who grew up in the northern latitudes of Europe and North America. MS is most prevalent in the Orkney Islands north of Scotland. The risk for MS decreases the closer you live to the equator.
Women are twice as likely as men to develop MS.
In the US, MS is most common among Caucasians. The prevalence of MS among Japanese-Americans and African-Americans is one-quarter and one-third that among Caucasians, respectively. The disease is extremely rare among Japanese living in Japan and among Africans living in Africa. These figures suggest that environment plays a role as well as genetics.
There are several conditions that cause symptoms similar to those of MS. Other diseases that mimic the symptoms of MS include other demyelinating diseases such as adrenoleukodystrophy and metachromatic leukodystrophy, chronic infection such as Lyme disease, and vitamin B12 deficiency. Your doctor will have to rule out these other possibilities before diagnosing MS. You will not be formally diagnosed with MS unless you have had two symptomatic “attacks” affecting two distinct parts of the body.
A neurologist will perform a neurological examination to confirm the diagnosis of MS, and to identify which nerve pathways are affected by the disease. If your general internist suspects that you have MS, you will be referred to a neurologist who can confirm a diagnosis. The neurologist will conduct several tests to search for uncoordinated eye movements and other vision problems, weakness or loss of sensation in various parts of the body, difficulty in walking and coordinating other movements, and inflammation of the optic nerve. The neurologist will also look for Lhermitte’s sign, in which flexion of the neck produces an electrical sensation that runs down the arms and spine. He or she will also examine a number of other reflexes and neurological signs to determine whether you have MS, and if so, what parts of the nervous system are affected.
A spinal tap may be performed so that the cerebrospinal fluid (CSF) can be analyzed. In a spinal tap (lumbar puncture), a needle will be inserted between two vertebrae to withdraw a small amount of cerebrospinal fluid for analysis. You will receive local anesthetic before the procedure, and will generally lie on your side with your knees and chin tucked toward your chest. A spinal tap may be performed on an inpatient or outpatient basis.
Since MS is an inflammatory condition caused by a misdirected immune response, and because the immune system works by making white blood cells and antibodies in response to a perceived threat, a person with MS may have more white blood cells and high levels of certain antibodies in the CSF.
An MRI test can be used to confirm the diagnosis, determine how far the disease has progressed. An MRI is a radiological test that will identify parts of the brain and spinal cord where myelin has been lost. However, since other diseases can cause such scarring, an MRI should never be the only tool used to diagnose MS.
A neurological test of evoked potentials may be used to find abnormalities in nerve pathways. In an evoked potentials test, electrodes are attached to the patient’s scalp to measure electrical activity in the brain after visual, auditory, and sensory stimulation. This test can measure the speed at which impulses travel along various nerve pathways, and can help to find where demyelination has occurred. This test is used when symptoms are absent, or when a diagnosis has been elusive or difficult.
Other tests used to evaluate patients with MS include a detailed examination of vision by an ophthalmologist and a CT scan of the brain. A CT scan can be used to check for lesions in the brain, spinal cord, and other parts of the nervous system. A careful vision examination can detect damage to the nerves involved in vision, such as the optic nerve.
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