Phylicia Allen

Honors Biology

Professor Hunnicutt

What are the

Odds?

Myasthenia Gravis affects

approximately 2 out of every

100,000 people and can

occur within any age, race, or

sex. According to these odds

this is more likely to happen

than

•Finding a four-leaf clover on

the first try

•Being murdered

•Being considered possessed

by Satan.

A chronic autoimmune neuromuscular disease characterized

by varying degrees of weakness of the skeletal (voluntary)

muscles of the body.

The hallmark of myasthenia gravis is muscle weakness that

increases during periods of activity and improves after

periods of rest. Muscles that control eye and eyelid

movement, facial expression, chewing, talking, and

swallowing are often, but not always, involved in the

disorder. (muscles that control breathing and neck

movements also may be affected.)

What causes myasthenia

gravis…

MG is caused by a defect in the transmission of

nerve impulses to muscles, occurring when

normal communication between the nerve and

the muscle is interrupted at the neuromuscular

junction, the place where nerve cells connect

with the muscles they control.

Impulses travel down the nerve and the nerve

endings normally release a neurotransmitter

substance called acetylcholine. Acetylcholine

travels through the neuromuscular junction and

binds to the acetylcholine receptors which are

activated and generate a muscle contraction.

In MG, antibodies block, alter, or destroy the

receptors for acetylcholine at the

neuromuscular junction which prevents the

muscle contraction from occurring.

With MG, normal communication between the nerve

and muscle is stopped at the place where nerve

endings connect with the muscles they control—the

nerve muscle junction. Normally, the nerve endings

release a substance called acetylcholine, which binds

the muscle tissue at the nerve-muscle junction, causing

the muscle to contract. In someone with MG, the

body’s own immune system makes antibodies that

block the binding of acetylcholine to the muscle.

The role of the thymus

gland in myasthenia

gravis…The thymus gland lies in the upper chest

area beneath the breastbone and plays

an important role in the development of

the immune system in early life. It’s

somewhat large in infants, grows

gradually until puberty, and then gets

smaller and is replaced by fat with age. In

adults with MG, the thymus is abnormal.

Some individuals with MG develop

thymomas, or tumors of the thymus gland,

which are generally benign, but could

become malignant. Although the

relationship between the thymus gland

and MG is not yet fully understood,

scientists believe that it gives incorrect

instructions to developing immune cells,

ultimately resulting in autoimmunity and

the production of the acetylcholine

receptor antibodies, thereby setting the

stage for the attack on the neuromuscular

transmission.

•Drooping of one or both eyelids (ocular myasthenia gravis/ptosis)

•Blurred or double vision (diplopia)

•Problems walking (unstable or waddling gait)

•Weakness in arms, hands, fingers, legs, and neck

•Change in facial expression

•Having a hard time swallowing

(which leads to difficulty eating and ultimately extreme weight loss)

•Impaired speech (dysarthria)

•Shortness of breath (feeling like you can’t get enough air)

The onset of the disorder may be sudden. Symptoms often are not immediately recognized as myasthenia gravis. In most cases the most noticeable symptom is weakness of the eye muscles. In others, difficulty in swallowing and slurred speech may be the first signs. The degree of muscle weakness in MG varies greatly among patients, ranging from a localized form, limited to eye muscles, to a severe or generalized form in which many muscles-sometimes including those that control breathing-are affected.

Myasthenia gravis occurs in all ethnic groups and both

genders. It most commonly affects young adult women

(under 40) and older men (over 60), but it can occur at

any age.

MG in juveniles is common and is not directly inherited

nor is it contagious. However, the disease may

occasionally occur in more than one member of the

same family.

Diagnosis

It’s not uncommon in cases of MG for a delay in

diagnosis. The first step of diagnosis includes a

review of the individual’s medical history, and

physical and neurological examinations. If the doctor

suspects MG several tests are available to confirm

the diagnosis.

•Antibody blood tests: Blood tests detect the

presence of high levels of abnormal antibodies that

prevent normal nerve-to-muscle transmission.

•Edrophonium test: Drug is injected and weak eye

muscles will be temporarily strengthened.

•Nerve conduction test/repetitive stimulation: A

nerve linked with a specific muscle is stimulated to

see if the muscle action is weakened.

•Single fiber electromyography (EMG): Singe muscle

fibers are stimulated by electrical impulses. Muscle

fibers of people with MG do not respond to repeated

electrical stimulation as well as muscles that

function normally. Can detect problems with nerve-to-

muscle transmission.

•Computed Tomography (CT) or Magnetic Resonance

Imaging: Test shows if there is an abnormal thymus

gland or a thymus gland tumor.

There is no cure for MG, however there are several therapies that can

help strengthen the muscles of someone with MG.

•Medications: Drugs used including cholinesterase inhibitors, such as

pyridostigmine. These drugs help improve nerve signals to muscles and

increase muscle strength. Immunosuppressive drugs are used to

suppress the production of abnormal antibodies.

•Thymectomy: The surgical removal of the thymus gland, which is

abnormal in most persons with MG. The procedure is done for people

with MG who have tumors, as well as for some who don’t have tumors.

•Plasmapheresis: Procedure removes abnormal antibodies from the

blood, providing relief for MG symptoms for a few weeks.

•High-dose intravenous immune globulin: This treatment keeps the

immune system from damaging the nerve-muscle junction for a short

time. Provides relief from MG symptoms in many patients for weeks to

months.

Myasthenic Crises

Occurs when the muscles that control breathing

weaken to the point that ventilation is inadequate,

creating a medical emergency and requiring a

respirator for assisted ventilation. In patients whose

respiratory muscles are weak, crises-which generally

call for immediate medical attention-may be triggered

by infection, fever, or an adverse reaction to

medication.

Much has been learned about myasthenia gravis in recent years and, with treatment, the outlook for most patients with myasthenia gravis is

bright. They will have significant improvement of their muscle weakness and they can expect to lead normal or nearly normal lives. Some cases

of MG go into remission temporarily and muscle weakness may disappear completely so that medications can be discontinued. Stable,

long-lasting complete remissions are the goal of Thymectomy. Though much has been learned, there is still much more knowledge to gain. The

ultimate goal of myasthenia gravis research is to increase scientific understanding of the disorder. Researchers are seeking to learn what

causes the autoimmune response in MG, and to better define the relationship between the thymus gland and MG. Today’s research includes a broad spectrum of studies conducted and supported by

NINDS (National Institute of Neurological Disorders and Stroke) scientists, who are evaluating new and improving current treatments for the disorder. The objective of the study is to expand current knowledge

of the function of receptors and to apply this knowledge to the treatment of MG.

In July of this past year, I was diagnosed with

Myasthenia Gravis and immediately admitted to the

pediatric oncology unit of the Florida Hospital. By the

time of my diagnosis I had lost over 50 pounds and

reached crisis status. So much of my digested foods

had been inhaled into my lungs that I was beginning to

develop pneumonia. Since my diagnosis, I’ve been

undergoing treatment for the condition and have been

extremely satisfied with the results. I’ve never felt better

and couldn’t be happier.