Myasthenia Gravis (MG)

What is myasthenia gravis (MG)?

Deriving from the Greek and Latin words for “grave muscle weakness,” the very literally named myasthenia gravis (or MG) is the most common autoimmune neuromuscular disorder. People with MG experience varying degrees of weakness and fatigue in voluntarily controlled muscles groups. The more active the individual is at any given time, the more their symptoms may worsen. Resting usually allows symptoms to improve again. Myasthenia gravis currently has no cure and the symptoms are known to be progressive. However, the prognosis is far from “grave.” Only 10 percent of people with MG develop life-threatening respiratory complications. Instead, the majority of people not only live to an expected age, but treatment can drastically reduce MG’s impact on their daily lives. A subset of patients remains refractory to these traditional treatment options, which leads to refractory generalized myasthenia gravis (gMG). Myasthenia gravis impacts an estimated 20 per 100,000 individuals globally. The subdivisions of MG—including congenital myasthenia gravis, transient neonatal myasthenia gravis, and juvenile myasthenia gravis—occur more rarely.

What causes myasthenia gravis?

Myasthenia gravis is most often an autoimmune disorder, meaning it is not inherited and does not require any sort of family history. The condition develops as a result of the body attacking itself. Antibodies that should be acting against foreign invaders like germs instead target proteins necessary for nerves and muscle cells to communicate. As if they’re computers connected to a poor wifi network, the muscles can’t read signals from the brain, causing MG’s characteristically delayed muscle response and weakness.

How do people inherit myasthenia gravis?

Contrary to the description above, there is one form of MG that can be inherited: congenital myasthenia gravis (also called congenital myasthenia syndrome). This form of MG is a genetic disorder; rather than antibodies disrupting the proteins involved in regular neurotransmitter activity, gene mutations change the proteins so they can no longer complete their intended functions. Congenital myasthenia gravis is very rare compared to its autoimmune “cousin.” It’s usually inherited through both parents, with mutations occurring in the RAPSN, CHAT, DOK7, COLQ, and, most commonly, in the CHRNE gene. While it’s unknown how frequently congenital myasthenia gravis occurs, cases in medical literature number in the estimated 600s.

What are common symptoms of myasthenia gravis?

In general, myasthenia gravis symptoms can begin at any age and worsen with activity. However, there are a few differences in onset for the three MG subdivisions:

• Congenital myasthenia gravis begins in infancy and lasts a lifetime
• Transient neonatal myasthenia gravis also beings in infancy, but ends within a few weeks of birth
• Juvenile myasthenia gravis starts in adolescence (usually in women) and may fall in and out of remission throughout a person’s life

Regardless of type, myasthenia gravis causes weakness and fatigue in skeletal muscles—any voluntarily controlled, skeletal muscle group. Most people notice it in the arm and leg muscles, as well as in the muscles around the eyes, mouth, and throat. Some manifestations include:

• Drooping eyelids
• Double vision
• Trouble swallowing or chewing (dysphagia)
• Slurred speech
• Changed gait
• Neck or limb weakness/fatigue
• A small percentage of people may also develop a weakness in the chest wall that could lead to life-threatening breathing difficulties.

How is myasthenia gravis diagnosed?

Getting a proper diagnosis of any form of myasthenia gravis is easier said than done. Muscle weakness, the key characteristic of MG, can be linked to multiple other disorders, and there is no one “myasthenia gravis test” that guarantees an accurate diagnosis. If doctors suspect myasthenia gravis is a possibility, they can conduct a thorough examination and review the individual’s medical history. They may rely on one or more tests, such as blood tests or an electromyography (EMG), to reach a diagnosis. Some doctors even recommend starting a myasthenia gravis medication and using the individual’s response to provide confirmation.

What treatment options are available for myasthenia gravis?

While there is currently no cure, there are a variety of myasthenia gravis medications and treatment courses. These may include steroids, plasmapheresis, or surgery to remove the thymus gland (which has an unknown correlation with MG symptoms). Factors like age help determine treatment course and effectiveness. Even so, many find that myasthenia gravis medications improve muscle strength and general function. In a small number of cases, myasthenia gravis medications can actually induce periods of remission. With that being said, those with a more severe progression of MG, especially in regards to breathing, may need additional support.

Where can I find more information about myasthenia gravis (MG)?

• John Hopkin’s Medicine Health Library
• National Institute of Neurological Disorders and Stroke
• Myasthenia Gravis Foundation of America, Inc.
• U.S. National Library of Medicine:
  • Myasthenia Gravis
  • Congenital Myasthenia Gravis