Myasthenia Gravis: An Autoimmune Disorder

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  • 0:07 Autoimmune Disease
  • 0:51 What is Myasthenia Gravis?
  • 1:45 What Does M.G. Occur?
  • 5:16 Signs, Symptoms & Diagnosis
  • 6:54 Treatment of M.G.
  • 7:34 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson will go over a condition called myasthenia gravis. We'll talk about why it occurs, how your immune system is involved, how it can be treated, if it's curable, and what typical signs it produces in a person.

Autoimmune Disease

Most every one of us has played a game called 'monkey in the middle', or something along those lines. It's basically where at least one person stands in between at least two other people who throw or kick an object like a ball to one another. The role of the monkey in the middle is to block the ball from getting through to the other person. Typically, as was the case when I was the monkey in the middle, the person in the middle has a hard time intercepting the ball.

But in some cases of autoimmune diseases, diseases where your own body attacks itself, the monkey in the middle is devastatingly effective. So effective, in fact, that it causes serious problems, as this lesson will address.

What is Myasthenia Gravis?

The terrible game that our body plays with us isn't called monkey in the middle, it's called myasthenia gravis. This is an incurable autoimmune disease that leads a person to develop severe muscle weakness and fatigue.

Although, as with many diseases, myasthenia gravis can occur at almost any age, it seems to affect more women under 40 and more men over 60 years of age, and in the United States affects about 20 individuals for every 100,000 members of the population.

Some of the most famous people in the world have suffered from this terrible disease, such as Aristotle Onassis, the billionaire Greek shipping magnate who married Jackie Kennedy after JFK's assassination.

Why Does Myasthenia Gravis Occur?

Scientists are still working out the details of why myasthenia gravis may occur. We know that everything from genetics to immune reactions to drugs may increase the likelihood of developing this condition. Some researchers also believe the thymus , an organ located underneath your breastbone that is responsible for the proper development of the immune system, may play a role in the aberrations that occur in this disease. It has been noted that certain individuals with myasthenia gravis have a thymoma, or a tumor of the thymus.

What we do understand a bit better is the end result of most cases of myasthenia gravis. In this condition, your own body produces little proteins called autoantibodies, which are antibodies that target an individual's own body, organs, cells, and receptors for destruction or inactivation.

Normally, antibodies are supposed to target foreign invaders such as bacteria and viruses for destruction or inactivation. But in an autoimmune condition such as myasthenia gravis, the antibodies become directed against auto, or self.

Specifically, these autoantibodies attach themselves to the receptors on the skeletal muscles of your body; these are the muscles responsible for locomotion. By doing so, the antibodies prohibit the receptors on the muscles from receiving a specific signal or destroy the receptors outright. Namely, this signal comes from nerves innervating the skeletal muscles. These nerves release a neurotransmitter that activates muscles of locomotion, called acetylcholine.

Under normal conditions, the nerves release this acetylcholine and it lands on its receptor on the muscle the nerve innervates. Once it lands on the receptor on this muscle, the muscle gets all excited, contracts, and allows you to move. The release of acetylcholine occurs at the neuromuscular junction, the place where nerves meet the muscles they innervate. The space between the nerve ending and the muscle it controls is known as the synaptic cleft.

That's what happens normally. However, in people with myasthenia gravis the autoantibodies bind to the receptors on the muscle cells and thereby destroy or inactivate them.

You can liken the autoantibodies to our monkey in the middle, the nerve and muscle to our two players, the space between the two players as the synaptic cleft, the acetylcholine to our ball, and the receptors on the muscle cells to the hands of our player called 'the muscle.'

The nerve player wants to pass the ball to the muscle player, but the monkey latches onto the hands of the muscle player and blocks the muscle player from ever catching the ball. If the ball can't pass from one end to the other and can't land in the muscle's hands because those hands are blocked by the monkey, then the muscle player cannot become all excited about catching the ball, becomes depressed instead, and refuses to move because the game is no fun anymore.

Clinical Signs, Symptoms, and Diagnostics

Since the muscles are no longer excited to move, you shouldn't be shocked by the typical signs and symptoms associated with myasthenia gravis, which means 'grave muscle weakness' through its ancient Latin and Greek roots. These signs include:

  • Difficulty walking, eating, speaking, smiling, and swallowing
  • Droopy eyelids and double vision
  • In serious cases, respiratory failure, when the muscles of respiration can no longer work.

There are several ways by which a person with this condition can be diagnosed, including running bloodwork that identifies the autoantibodies I mentioned before.

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