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6 Types of Myasthenia Gravis: What Are the Differences?

Posted on January 23, 2024

If you or a loved one has been diagnosed with myasthenia gravis, you may wonder about the various types and how they are different. Doctors typically divide myasthenia gravis into three categories based on:

  • The part of the body affected by myasthenia gravis symptoms
  • The types of immune system proteins (antibodies) a person has
  • The person’s age at diagnosis

This article explores the types of myasthenia gravis and how your doctor may classify them. The type you have will play a role in the myasthenia gravis symptoms you experience and which treatment options your doctor may recommend.

Myasthenia Gravis Based on Affected Areas of the Body

Myasthenia gravis is an autoimmune disorder, meaning that the body’s own immune system attacks healthy cells and tissues. Specifically, the immune system creates proteins known as autoantibodies that tag certain parts of muscle cells for destruction. This process causes weakness in any of the body’s voluntary or skeletal muscles (the muscles we control on demand).

There are two main types of myasthenia gravis — ocular myasthenia gravis (which involves symptoms affecting the eyes) and generalized myasthenia gravis. The treatments for ocular and generalized myasthenia gravis are typically the same. Doctors may prescribe:

  • Immunosuppressive drugs such as azathioprine (Imuran and Azasan) to dampen the immune system
  • Corticosteroids such as prednisone to control inflammation
  • Acetylcholinesterase inhibitors, such as pyridostigmine (Mestinon)

Depending on details about the type of myasthenia gravis you have, your doctor may recommend newer, targeted drugs such as:

1. Ocular Myasthenia Gravis

People with myasthenia gravis usually notice ocular symptoms as the first sign of their condition. They may have ptosis (droopy eyelids) due to weakened eyelid muscles. One or both eyes may be affected. In some cases, your eyelids may be so weak that you have trouble seeing.

Myasthenia gravis can also affect the extraocular muscles. These muscles attach to the eyeball and control its movement within the eye socket. People with weakened eye muscles from myasthenia gravis can develop diplopia (double vision). Your brain and eye muscles work hard to keep your eyes aligned and your vision sharp. Double vision occurs when the eyes become misaligned, causing you to see the same object in two different locations.

Overall, more than half of people with myasthenia gravis develop droopy eyelids and double vision as the first signs of the condition. Around 15 percent of people with ocular myasthenia gravis never progress to generalized myasthenia gravis.

2. Generalized Myasthenia Gravis

Roughly 50 percent of people who experience ocular symptoms will go on to develop generalized myasthenia gravis within two years. Muscle weakness in generalized myasthenia gravis tends to spread from the top of the body down. At first, you may notice symptoms affecting your face, jaw, and neck. This is known as bulbar weakness because it affects the nerves that come from the bulblike area of the brainstem.

Around 15 percent of people with generalized myasthenia gravis experience symptoms from bulbar weakness, according to the Muscular Dystrophy Association. These include difficulties with:

  • Chewing
  • Swallowing (known as dysphagia)
  • Talking (known as dysarthria), causing speech to sound nasally or slurred
  • Controlling facial expressions

Muscle weakness in generalized myasthenia gravis can also continue spreading downward, affecting the arms and hands, then the legs. People with generalized myasthenia gravis may have trouble standing up from a sitting position, climbing stairs, or lifting their arms over their heads.

Myasthenia Gravis Based on Antibody Type

People with myasthenia gravis typically have one of three types of autoantibodies, or immune proteins attacking the tissues, that cause their symptoms. The type of autoantibodies you have can play a role in your symptoms and what treatments may work best.

3. Acetylcholine Receptor Antibody-Positive Myasthenia Gravis

Our nerves and muscles use the chemical messenger acetylcholine to communicate with one another. Acetylcholine sends signals through the neuromuscular junction (NMJ), the space between nerve endings and muscle fibers.

When your nerves send a signal for your muscles to move, they release acetylcholine into the NMJ. Your muscle cells have acetylcholine receptors (AChRs) on them that act like a net to “catch” (bind with) the acetylcholine molecules. When the receptors bind with acetylcholine, your muscles receive the message to contract.

People with myasthenia gravis have autoantibodies that target and destroy AChRs. Without enough receptors to catch acetylcholine molecules, the muscles can’t contract properly. This causes muscle weakness associated with myasthenia gravis. Studies show that around 85 percent of people with myasthenia gravis have AChR autoantibodies (also known as anti-AChR antibodies).

Those who have AChR antibodies are also more likely to experience generalized muscle weakness or a combination of ocular and generalized symptoms. On the other hand, people who are negative for AChR antibodies tend to only have ocular myasthenia gravis.

4. Muscle-Specific Kinase Antibody-Positive Myasthenia Gravis

If tests for AChR antibodies are negative, doctors may also test for muscle-specific kinase (MuSK) antibodies. These antibodies interfere with signals in the NMJ. MuSK antibodies are less common than AChR antibodies. In fact, studies from the journal Frontiers in Neurology show that only 5 percent to 8 percent of people with myasthenia gravis have MuSK antibodies.

Some groups, especially females and Black individuals, are more likely to have MuSK antibody-positive myasthenia gravis, as cited in a study from Neurologic Clinics. This likelihood is higher when compared to males and white individuals. MuSK antibodies are also associated more with bulbar weakness and less with ocular symptoms.

Researchers have learned that people with MuSK antibody-positive myasthenia gravis don’t respond as well to anticholinesterase medications as others with myasthenia gravis. In total, around 16 percent of those with MuSK antibodies respond to this type of treatment, according to Neurologic Clinics, and 20 percent experience a negative reaction or worsening of symptoms. If you have MuSK antibody-positive myasthenia gravis, your doctor may prescribe an immunosuppressant instead.

5. Seronegative Myasthenia Gravis

People with seronegative or double-negative myasthenia gravis have no AChR or MuSK antibodies. Studies from the American Academy of Ophthalmology report that around 10 percent of people with myasthenia gravis have the seronegative type.

As cited in JAMA Neurology in 2011, researchers first reported that people with seronegative myasthenia gravis have low-density lipoprotein receptor-related protein 4 (LRP4) antibodies. LRP4 plays an important role in the NMJ, helping nerves and muscles communicate. LRP4 antibodies are uncommon — researchers have found that only 2 percent of those with myasthenia gravis have them.

As doctors have continued to learn more about seronegative myasthenia gravis, they’ve noticed some trends. People with seronegative myasthenia gravis tend to have ocular and bulbar weakness rather than generalized myasthenia gravis symptoms. This finding means that they tend to have double vision, droopy eyelids, and trouble speaking or swallowing. The American Academy of Ophthalmology has found seronegative myasthenia gravis tends to affect females more often and to develop in people at a younger age.

Studies from a 2023 issue of Brain Sciences show that people who have seronegative myasthenia gravis with LPR4 antibodies may be treated with typical myasthenia gravis therapies like acetylcholinesterase inhibitors. Immunosuppressants and plasmapheresis (a treatment that filters blood to remove antibodies) may also be effective.

Myasthenia Gravis Based on Age at Diagnosis

Myasthenia gravis can affect anyone at any age, although it’s more common in men over the age of 60 and women under the age of 40, according to Mayo Clinic. Doctors usually describe myasthenia gravis as:

  • Early-onset — Affects adults ages 40 and younger
  • Late-onset — Affects adults over the age of 40

Myasthenia gravis can also develop in children, which is known as juvenile myasthenia gravis. Symptoms of the condition may vary in younger individuals, affecting their growth and development. Treating this form often requires special approaches designed specifically for children.

6. Juvenile Myasthenia Gravis

According to the Children’s Hospital of Philadelphia, myasthenia gravis is a rare condition affecting around 10 in 1 million people. Of those who are diagnosed, around 10 percent of them are children. Juvenile myasthenia gravis causes symptoms similar to those seen in adults. Children with juvenile myasthenia gravis may also have droopy eyelids, double vision, and trouble walking.

Many cases of juvenile myasthenia gravis are caused by abnormal growth in the thymus, known as thymic dysplasia. The thymus gland is responsible for creating and training immune cells to help fight infections. In children with juvenile myasthenia gravis, the thymus may be affecting the immune system, doing more harm than good. Juvenile myasthenia gravis can be treated with thymectomy (surgery to remove the thymus), which usually improves myasthenia gravis symptoms.

Like adult-onset myasthenia gravis, juvenile myasthenia gravis can also be treated with anticholinesterase inhibitors and immunosuppressants. Your child’s doctor will recommend the most effective dose to address their symptoms while reducing the risk of unwanted side effects.

If you or a loved one is living with myasthenia gravis, you’ll need to gain a good understanding of this autoimmune disorder. This examination of the six types, detailing how they affect the body, different antibody patterns, and age-related distinctions, gives a clearer roadmap for grasping the condition. Whether it’s droopy eyelids, double vision, or generalized muscle weakness, recognizing symptoms and how they may change over time is crucial. With this knowledge, you and your support networks can improve your ability to navigate discussions with your doctors.

Find Your Team

On MGteam, the social network for people living with myasthenia gravis and their loved ones, members come together to ask questions, give advice, and share their stories with others who understand life with myasthenia gravis.

Are you living with myasthenia gravis symptoms? What type of myasthenia gravis do you have? Share your experience in the comments below, or start a conversation by posting on your Activities page.

References
  1. Myasthenia Gravis — StatPearls
  2. Myasthenia Gravis (MG) — Cleveland Clinic
  3. Autoantibody Specificities in Myasthenia Gravis; Implications for Improved Diagnostics and Therapeutics — Frontiers in Immunology
  4. Myasthenia Gravis (MG) — Muscular Dystrophy Association
  5. Ocular Myasthenia Gravis — Brigham and Women’s Hospital
  6. Ocular MG — Myasthenia Gravis Foundation of America
  7. Extraocular Muscles — American Academy of Ophthalmology EyeWiki
  8. Acetylcholine (ACh) — Cleveland Clinic
  9. Myasthenia Gravis — NORD
  10. Autoimmune MG and Diagnostic Tests — Myasthenia Gravis Association of America
  11. Clinical Manifestations of Acetylcholine Receptor Antibody Positive and Negative Myasthenia Gravis — Journal of the Medical Association of Thailand
  12. Acetylcholine Receptor Antibody (Blood) — University of Rochester Medical Center
  13. Myasthenia Gravis With Antibodies Against Muscle Specific Kinase: An Update on Clinical Features, Pathophysiology and Treatment — Frontiers in Molecular Neuroscience
  14. MuSK-Associated Myasthenia Gravis: Clinical Features and Management — Frontiers in Neurology
  15. MuSK and Myasthenia Gravis Due to Other Antibodies — Neurologic Clinics
  16. Seronegative Myasthenia Gravis — EyeWiki
  17. Autoantibodies to Lipoprotein-Related Protein 4 in Patients With Double-Seronegative Myasthenia Gravis — JAMA Neurology
  18. Myasthenia Gravis: Autoantibody Specificities and Their Role in MG Management — Frontiers in Neurology
  19. Diagnosis and Management of Seronegative Myasthenia Gravis: Lights and Shadows — Brain Sciences
  20. Myasthenia Gravis — Mayo Clinic
  21. Myasthenia Gravis: Life Expectancy — RareDiseaseAdvisor
  22. Myasthenia Gravis — Children’s Hospital of Philadelphia
    Posted on January 23, 2024
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    Luc Jasmin, M.D., Ph.D., FRCS (C), FACS is a board-certified neurosurgery specialist. Learn more about him here.
    Emily Wagner, M.S. holds a Master of Science in biomedical sciences with a focus in pharmacology. She is passionate about immunology, cancer biology, and molecular biology. Learn more about her here.

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