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Muscular and Bone
 What
Is Myasthenia
Gravis (MG)
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What
Is Myasthenia Gravis |
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What Is Myasthenia Gravis?
Myasthenia gravis is a chronic disorder characterized by weakness and rapid
fatigue of any muscles under your voluntary control. It results from a breakdown
in the normal communication between nerves and muscles.
The disorder leaves your nerves and muscles healthy, and the muscle weakness
you experience improves with rest. In moderate to severe cases,
myasthenia gravis may cause difficulties with speech, chewing, swallowing
and breathing, as well as weakness of your limbs.
Myasthenia gravis is rare but affects both children and adults. It's most common
in women younger than age 40 and in men older than age 60. Treatments can't
cure myasthenia gravis, but they can relieve symptoms
Signs and Symptoms
Myasthenia gravis may affect any of the muscles that you voluntarily control.
It more commonly affects certain muscles, including those of the face, eyes, arms
and legs, and those involved in chewing, swallowing and breathing. Signs and
symptoms may include:
Facial muscle weakness, including drooping eyelids
Double vision
Difficulty in breathing, talking, chewing or swallowing
Muscle weakness in the arms or legs
Fatigue brought on by repetitive motions
The more a muscle action is repeated, the worse the weakness becomes.
In myasthenia gravis, good days alternate with bad. Remissions may occur,
however, and may last for months. In rare cases, breathing or swallowing
problems worsen, requiring emergency medical care.
Causes
When your nervous system is functioning normally, the chemical acetylcholine
transmits nerve impulses to your muscles. At specialized areas of your muscles,
called neuromuscular junctions, receptor sites receive impulses and signal your
muscles to contract in daily movements, such as raising a spoon to your mouth.
In myasthenia gravis, there's a breakdown in communication between your nerves
and muscles. The culprit is your immune system. For unknown reasons,
myasthenia gravis causes your immune system to produce antibodies that block
or destroy many of your receptor sites up to 80 percent of them. With fewer
receptor sites, your muscles receive fewer nerve signals, causing the weakness.
It's believed that the thymus gland, a part of your immune system located in the
upper chest beneath the breastbone, may trigger or maintain the production of
these antibodies. Large in infancy, the gland shrinks in healthy adults. However,
some people with myasthenia gravis have abnormally large thymus glands.
About 15 percent develop tumors of the thymus.
Some factors can make myasthenia gravis worse, including illnesses such as a
cold, stress and overexerting yourself
When To Seek Medical Advice
If you experience muscle weakness or have difficulty controlling the muscles of
your eyes, face and mouth, difficulty breathing or fluctuating weakness in your
arms and legs, see your doctor. These could be indications of myasthenia gravis.
Although there's no cure for myasthenia gravis, the outlook for managing its
symptoms is good. The sooner you see your doctor, the sooner treatments can
help you improve your muscle strength and the sooner you can learn about
strategies that can help you use your energy in the most efficient ways.
Screening And Diagnosis
The key symptom that points to the possibility of myasthenia gravis is muscle
weakness that improves with rest. Tests to confirm the diagnosis may include:
Neurologic examination. This may include testing of your reflexes, muscle
strength, muscle tone, senses of touch and sight, gait, posture, coordination,
balance and mental skills.
Electromyography. During the first part of this test, a small electrical impulse is
applied to your skin to stimulate your nerves to test the strength of your muscle
contraction. In the second part, a thin-needle electrode inserted into one of your
muscles helps measure patterns of electrical activity in your muscle at rest and
with slight muscle contraction.
Blood analysis. A blood test may reveal the presence of abnormal antibodies
that disrupt the receptor sites where nerve impulses signal your muscles to move.
Edrophonium chloride test. Injection of the chemical edrophonium chloride
(Tensilon) may result in a sudden, although temporary, improvement in your
muscle strength, an indication that you may have myasthenia gravis.
Edrophonium chloride acts to block an enzyme that inhibits the transmission of
signals from your nerve endings to your muscle receptor sites.
Treatment
There is no cure for myasthenia gravis. But these treatments, alone or in
combination, relieve symptoms for many people:
Medications. Several drugs, called cholinesterase inhibitors, enhance
communication between nerves and muscles. These drugs don't treat the
underlying problem, but they do improve muscle contraction. Corticosteroids
inhibit the immune system, limiting antibody production. Prolonged use of
corticosteroids can lead to serious side effects, such as bone thinning,
weight gain, diabetes, increased risk of some infections and a redistribution
of body fat.
Surgery. Removal of the thymus gland brings marked relief to about half the
people with severe myasthenia gravis, but the effect is often delayed for many
years and the response is more dramatic in younger people.
Plasmapheresis (plaz-muh-fuh-RE-sis). This procedure can remedy
life-threatening stages of myasthenia gravis. Plasmapheresis involves removal
of antibodies from your blood that block transmission of signals from your nerve
endings to your muscle's receptor sites. Blood is taken from your body, passed
through a filter that removes the specific antibodies and then is returned to your
body. This approach is expensive and time-consuming. Also, other forms of
therapy are necessary for long-term restoration of muscle strength. Otherwise,
the immune system soon makes new antibodies to replace those that have been
removed.
As part of your treatment, your doctor may suggest physical therapy and
occupational therapy to help you adjust to tasks you need to do around the house
and in your job.
Coping Skills
Supplementing your medical care with these approaches may help you make the
most of your energy and cope with the symptoms of myasthenia gravis:
Adjust your eating routine. Try to eat when you have good muscle strength,
possibly an hour after taking your medication. Also, take your time eating and
rest between bites. Try soft foods and avoid sticky foods.
Use safety precautions at home. Install grab bars or railings in places where you
may need support, such as when you're getting out of the tub. Keep the floors and
halls in your house clear of clutter, cords and loose rugs. Outside your home, keep
the steps, sidewalk and path to your car clear.
Use electric appliances and power tools. Save your energy in the bathroom, in the
kitchen or at the workbench by using electric appliances such as toothbrushes,
can openers and screwdrivers.
Wear an eye patch. Using an eye patch can relieve double vision if you suffer
from this effect. Wear the patch while you read or watch television. To avoid
eyestrain, occasionally switch the patch from one eye to the other.
Plan ahead. If you have a chore to do around the house, shopping to do or an
errand to run, plan the activity to coincide with when your medication provides
your peak energy level. If you're working on a project at home, gather everything
you need for the project at one time, to eliminate extra trips that may drain your
energy.
Ask for help. Depending on your energy level, you may not be able to do
everything you planned around the house or run every errand that you need to.
Ask family members and friends to lend a hand.
Manage stress. Because emotional stress can make myasthenia gravis worse,
look for ways to reduce stress. These may include relaxation techniques such as
biofeedback and meditation.
Safety and Myasthenia Gravis
Studies show that most accidents with injuries occur in the home.
The Myasthenia Gravis patient who may have double vision, trouble walking, and
general muscle weakness is at greater risk for injury.
To assist the myasthenia gravis patient, following are suggestions for safety in the
home.
In the Bathroom
Put grab bars by the tub or shower.
Use a shower chair with rubber grips in the tub or shower.
An elevated toilet seat and/or rails may be helpful.
Put non-slip strips or a mat in the tub or shower.
Use a hand-held shower head to make it easier to check the water temperature
and to help in bathing and rinsing off.
If unsure of yourself in the bath or shower, have someone on stand-by for help.
Be sure to mop up any water on the floor and have bath mats and rugs secured to the floor with tape or a rubber gripper under the rug.
Other Rooms
Remove area throw rugs.
Tape down edges of large rugs.
Have rails on both sides of staircases and check any rugs on the stairs to make
sure they are securely attached to the stairs.
Do not wax floors.
Pad sharp corners on shelves and furniture by taping a small towel on the corners.
Put furniture along walls and do not change the arrangement of furniture, if possible
Repair holes and rough spots in floors and steps
Keep clutter, toys, and any small items off the floor.
Move electrical and telephone cords out of walkways.
Mop up spills on the floor immediately.
Provide bright lighting throughout the house.
Keep small night lights on, especially in the bedroom, bathroom, stairs, and kitchen.
Have emergency lighting, such as flash lights, in a convenient location in case of power outages.
Remove wheels or casters from bed or chairs.
Place the bed within easy reach of telephone. lights, and bathroom.
Place a bell or whistle by the bed to use to call for help.
Wear low heeled shoes with non-slip soles. Bare feet are safer than socks or soft slippers.
If you must hold onto furniture or walls, obtain a cane or walker and arrange to have a therapist provide training on how to use the equipment.
Have smoke alarms on each floor of the house and make sure they work.
Have emergency numbers and a fire extinguisher readily available.
Outside the Home
Keep sidewalks and driveways repaired.
Walk on hard surfaces where you can see possible dangers such as holes or toys.
If possible, have hand rails on both sides of stairs.
If stairs are a problem to climb, a ramp can be used or built for easy access.
Have toys, tools, lawn equipment and other obstacles off the walk area.
In icy or snow conditions, have all walk-ways and steps clear. Avoid trying to do it
yourself. Apply cat litter or sand on the area to provide traction.
If your mailbox is far from the house, ask the post office to deliver your mail to the
door.
Other services, such as trash pick-up, newspaper delivery, and recycling pick-up,
can be contacted to pick-up at the house instead of curb side.
Reviewed/compiled by:
Tina M. Vassar, RN, MSN, CS
This publication has been approved by the National Medical Advisory Board.
Myasthenia Gravis Foundation, 1996.
Diagnosis/Symptoms
The Creatine Kinase Test
Almost everyone with a neuromuscular disorder has had, or will have, a
creatine kinase test. But what exactly is creatine kinase (CK), and why are its levels
measured in neuromuscular diseases?
CK, also known as phosphocreatine kinase, or CPK, is a type of protein called an
enzyme. It catalyzes, or "encourages," a biochemical reaction to occur. The
normal function of CK in our cells is to add a phosphate group to creatine, turning
it into the high-energy molecule phosphocreatine. Phosphocreatine is burned as a
quick source of energy by our cells.
However, the normal function of CK isn't as relevant, in this case, as what happens
to CK when muscle is damaged. During the process of muscle degeneration,
muscle cells break open and their contents find their way into the bloodstream.
Because most of the CK in the body normally exists in muscle, a rise in the amount
of CK in the blood indicates that muscle damage has occurred, or is occurring.
To measure CK levels, a blood sample is taken and separated into fractions that
contain cells and a fraction that doesn't the serum. The amount of CK in the
serum is reported in units (U) of enzyme activity per liter (L) of serum. In a healthy
adult, the serum CK level varies with a number of factors (gender, race and activity),
but normal range is 22 to 198 U/L (units per liter).
Higher amounts of serum CK can indicate muscle damage due to chronic disease
or acute muscle injury. For this reason, if you're scheduled to have blood drawn
for a CK test to diagnose a potential muscle disorder, you should limit your
exercise to normal activities before the test.
CK tests are used to evaluate neuromuscular diseases in five basic ways:
To confirm a suspected muscle problem before other symptoms occur
To determine whether symptoms of muscle weakness are caused by a muscle
or a nerve problem
To differentiate between some types of disorders such as dystrophies versus
congenital myopathies
To detect "carriers" of neuromuscular disorders, particularly in Duchenne
muscular dystrophy. A carrier has a genetic defect, but doesn't get the full-blown
disease. A carrier's child may have the full disease.
To follow the course of a disease that fluctuates (primarily the inflammatory
myopathies), or to document episodes of acute muscle injury, as might occur in
some metabolic myopathies.
Because elevated CK levels indicate muscle damage, many parents wonder
why their children with Duchenne muscular dystrophy (DMD) had higher CK levels
when they were younger and had more muscle function. This seeming paradox
occurs because muscle degeneration is more rapid at the earlier stages and,
possibly, because there's more muscle bulk available to release CK into the
circulation at this time.
CK levels can be slightly elevated (500 U/L) in nerve disorders like
Charcot-Marie-Tooth disease, amyotrophic lateral sclerosis or spinal muscular
atrophy, or grossly elevated (3,000 to 3,500 U/L) in DMD or inflammatory
myopathies.
During episodes of acute muscle breakdown (rhabdomyolysis), CK levels can
temporarily go off the scale, topping out at 50,000 to 200,000 U/L. At the same time,
some neuromuscular disorders, such as the congenital myopathies (nemaline,
central core disease and others) and myasthenia gravis, may not trigger any
elevation of CK levels. CK levels don't always reflect the level of functional impact
on the individual.
Electromyography and Nerve Conduction Velocities
Diagnosis of neuromuscular disease hinges on a doctor's ability to identify a
specific defect of neuromuscular function. Sometimes, a doctor can infer this
functional defect - and the disease associated with it - by giving a physical exam,
doing a blood test or looking at the anatomy of nerves and muscles.
But other times, the doctor may have to directly evaluate the functions of nerves
and muscles and the connections between them by using two complementary
techniques - nerve conduction velocity testing (NCVs) and electromyography
(EMGs).
Action Potentials
Both NCV and EMG rely on the fact that the activity of nerves and muscles
produces electrical signals called action potentials. A nerve is actually a bundle
of axons, cables that conduct action potentials from one end of a nerve cell (or
neuron) to the other.
In motor neurons (neurons that connect to muscle), these action potentials travel
toward the muscle, where they cause release of a chemical called acetylcholine.
Acetylcholine opens tiny pores in the muscle, and the flow of sodium and
potassium ions through these pores creates action potentials in the muscle,
leading to contraction.
In NCV and EMG, these tiny electrical events are amplified electronically, then
visualized on a TV-like monitor called an oscilloscope and even heard using
audio equipment.
NCV and Axons
NCV measures action potentials conducted by axons, so doctors use it for
diagnosing diseases that primarily affect nerve function, such as different forms of
Charcot-Marie-Tooth disease (CMT).
It's done by placing surface electrodes (similar to those used for electrocardiograms)
on the skin at various points over a nerve. One electrode delivers a mild electrical
shock to the nerve, stimulating it to generate an action potential. The other
electrodes record the action potential as it's conducted through the nerve.
Doctors often use NCV to determine the speed of nerve conduction (hence, its
name). Conduction speed is influenced by a coating around axons, called myelin.
Myelin insulates each axon and normally forces action potentials to "jump" quickly
from one end of the axon to the other. If the myelin breaks down (as in CMT1), the
action potential travels more slowly.
NCV also can measure the strength of the action potential in the nerve, which is
proportional to the number of axons that contribute to it. If axons degenerate (as in
amyotrophic lateral sclerosis) or become clogged with debris (as in CMT2), the
action potential becomes smaller.
EMG and Muscle
An electromyogram measures the action potentials produced by muscles, and is
therefore useful for diagnosing diseases that primarily affect muscle function,
including the muscular dystrophies. Also, some EMG data can reveal defects in
nerve function.
In EMG, the doctor inserts a needlelike electrode into a muscle. The electrode
records action potentials that occur when the muscle is at rest and during voluntary
contractions directed by the doctor.
While a healthy muscle appears quiet at rest, spontaneous action potentials are
seen in damaged muscles or muscles that have lost input from nerve cells (as in
ALS or myasthenia gravis). During voluntary contraction, dystrophic (wasted)
muscles show very small action potentials, and myotonic (stiff) muscles show
prolonged trains of action potentials. Altered patterns of muscle action potentials
can indicate defects in nerve function.
A Little Discomfort
Though NCVs and EMGs are valuable tools for doctors, they can be distressing
for patients. Some people find the electric shocks of the NCV or the needle
penetration of the EMG uncomfortable or even painful. Young children might
struggle during the tests, making it difficult for doctors to carefully monitor nerve
and muscle activity. To ease discomfort, topical anesthetic can be applied to the
skin - but it won't prevent muscle pain during the EMG. Sometimes sedating
medications are needed to keep a child calm.
Partly because of these factors, NCVs and EMGs are generally used when it's not
possible to gather the right information from other diagnostic tests. Muscle biopsy
(excising and examining muscle tissue; see Quest, vol. 7, no. 4) can reveal
hallmark anatomical features of some neuromuscular diseases, making EMG
and NCV unnecessary. Genetic tests are now available for diagnosing some
diseases, and in those cases, EMG and NCV usually can be bypassed.
Nonetheless, NCV and EMG remain the gold standards for evaluating the function
of nerve and muscle. So, when a doctor suspects that a patient has a
neuromuscular disease that isn't clearly associated with anatomical or genetic
defects (like some types of CMT, or myasthenia gravis), NCV and EMG are
among the most valuable diagnostic tools
Common Questions Patients
Ask About
Thymectomy Surgery In Myasthenia Gravis
Myasthenia Gravis is often associated with enlargement of the thymus gland;
about 10% of MG patients have a tumor of the gland (thymoma). Since the 1940s,
MG has been treated with surgical removal of the thymus gland (thymectomy),
with the observation that most patients improve a year or so following surgery.
In general, a thymectomy is performed in patients under the age of 60, in those
with moderate or severe symptoms and in those suspected of having a thymoma.
The thymus gland is located in the upper chest under the breastbone. It is
composed of two main lobes and is shaped somewhat like a butterfly lying over
the windpipe. The exact role of the thymus in Myasthenia Gravis is not completely
understood.
When a thymectomy is being considered by the physician and patient, the referral
is made to a surgeon who has experience performing this type of surgery.
The surgeon then examines the patient and reviews the various medical records,
tests and x-rays. After learning about the surgery, including the preparation and
any possible complications, the patient and the surgeon make a decision on
whether or not to proceed with the surgery. In general, the patient should not
undergo thymectomy or any other surgery unless his or her physical condition is
good. Sometimes intravenous immune globulin (IVIg) or plasmapheresis can be
used to prepare a myasthenic for surgery.
A thymectomy is performed to improve the long-term clinical course of MG.
The response to thymectomy is variable; about 30% eventually experience
complete drug-free remission, and another 50% experience significant
improvement.
The following are some of the most common questions asked by a myasthenic
who is considering thymectomy surgery. Since each patients situation is unique,
it is essential to discuss these and all questions about this surgery with the
Myasthenia Gravis physician and surgeon.
How is surgery performed?
The surgery can be performed several ways. The first is the transsternal incision
in which the incision is made lengthwise on the chest and the breastbone (sternum)
is opened. This technique is the most widely used because it allows the surgeon
to be as certain as possible about the complete removal of the thymus. A second
type of incision is the transcervical, which is a smaller horizontal incision across
the lower part of the neck. A third type, video assisted or thorascopic surgery is
recent; data on its outcome for myasthenia is scarce. It is the least painful, and the
recovery time is shorter. With the thorascopic technique, surgeons only need to
make a small incision as well as small holes in to which to insert instruments.
The thorascopic contains a miniature camera; and surgeons watch what they are
doing on a video monitor. The surgeon will determine the optimal surgical
procedure, which may be based upon the position or number of lobes of the
thymus, as well as on experience and outcome data.
Intravenous Immunoglobulins
Common Questions Patients Ask About
IVIg Therapy In Myasthenia Gravis
What is IVIg?
IVIg is intravenous immune globulin. It is also known as pooled human gamma
globulin or simply, gamma globulin. IVIg has been used for decades in modern
medicine in the treatment of a variety of infectious or inflammatory diseases.
In patients who are lacking in the antibodies necessary to fight infection,
IVIg replaces those lost antibodies.
IVIg is used also in the treatment of a variety of autoimmune disorders. Over the
past two decades, IVIg has been used extensively in the treatment of some
autoimmune neurological disorders, including myasthenia gravis (MG). There are
indications that IVIg is an effective treatment for some patients with autoimmune
myasthenia gravis.
How does IVIg work?
IVIg seems to affect the function or the production of antibodies in the immune
system. The exact mechanism of how IVIg works in successfully treating
myasthenia gravis and other autoimmune disorders is not entirely understood.
Since IVIg is a blood product, is it safe?
IVIg is felt to be very safe with regard to exposure to infection or viruses. Donors
are screened. The processing of IVIg inactivates such infections as HIV, Hepatitis
B and C. Nonetheless, it is a human blood product that comes from multiple
donors.
Are there adverse effects that occur with IVIg treatments?
For the most part, IVIg is considered quite safe. However, there are several
adverse effects that may occur on occasion. Some patients develop headache,
chills, and aches during the infusion. Slowing the infusion and using medicines to
relieve these symptoms may be helpful.
Some patients will experience fatigue, fever, or nausea that may persist up to
24 hours after the infusion. Some patients may have migraine headaches,
aseptic meningitis, skin reactions or a more severe allergic type reaction.
Because IVIg is a highly concentrated protein, it can sometimes interfere with
blood flow and clotting.
Myasthenia Gravis Medication Information Card
(Drugs to be Avoided or Used with Caution in MG)
2000-2001
D-penicillamine and alpha-interferon should not be used in myasthenic patients,
as it they can cause MG. Botulinum toxin should be avoided.
Increased weakness in a significant number of MG patients has been reported
with the following drugs. Use only with caution and monitor for exacerbation of MG
symptoms: ? Neuromuscular blocking agents such as succinylcholine and
vecuronium- should only be used by an anesthesiologist familiar with MG
? Quinine, quinidine, or procainamide- avoid
? Selected antibiotics, particularly aminoglycosides and ciprofloxacin. Note: Many other antibiotics have been reported to increase MG weakness in occasional patients.
? Beta-blockers: propranolol, timolol maleate eyedrops
? Calcium channel blockers
? Iodinated contrast agents (a form of X-ray dye)
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