Definition (of MG)

MG Information > Definition (of MG)

What is this little known disorder which can strike fear into the hearts of the newly diagnosed and their families? It is not until you discover people who have been diagnosed and have learned to cope and lead fulfilling lives that you gain reassurance.

MG is a disorder which presents as acute attacks or chronic weakness of the voluntary muscles which increases with use and decreases with rest.

The muscles which we use all the time such as those which keep our eyelids open are often, but not always the first to indicate that something is wrong. Troubles with our facial muscles, the ones we use to smile, speak, or swallow are also among the first to reveal that there is a problem. Other symptoms which may, or may not, be present include:

Although the term Myasthenia Gravis (MG) is used most commonly in referring to the disorder there are some variations of the condition

Ocular Myasthenia, where the condition is only seen in the eye muscles.

Lambert Eaton Myasthenic Syndrome (LEMS) This is a different problem at the neuromuscular junction producing weakness without fatigue-ability. Unlike general MG if anything some people with LEMS improve with exercise.

Congenital Myasthenia (CM) is a condition with which one is born. The onset of symptoms may appear shortly after birth or may not show for some years.

CM is caused by a faulty gene affecting the nerve to muscle signalling. Because this is not an autoimmune problem, none of the immune treatments are suitable. Non-immunological treatments such as Mestinon may still however be useful in alleviating weakness.

In other cases babies born to Myasthenic mothers may, for a brief period of about four weeks, exhibit transient myasthenic symptoms. They fully recover if properly supported during this period while the mother’s antibodies clear from the baby’s blood.

As we have referred to differences in the way the nerves activate the muscles it is useful to describe, briefly, how our muscles work. MG is generally only found in the voluntary muscles. That is the ones which we control. For a voluntary muscle to contract, the brain transmits a signal to a specific nerve. The nerve endings are very close to the muscles but do not actually touch, the space between them is referred to as the neuromuscular junction. The nerve releases a chemical known as Acetylcholine (Ach) which travels across the gap to sites on the muscles known as AC receptors (AchR) This in turn activates the receptors to generate an electrical impulse along the muscle causing the muscle to contract. The malfunctioning of these receptors is at the root of the common form of autoimmune MG.

MG starts most commonly in young women, but also occurs in men and can start at any age. As patients often have the condition for many years and grow older with it, there are actually more older women than younger women with the condition at any time. In other words it is no respecter of race, age or gender.

We cannot describe MG without reference to the Thymus Gland (not to be confused with the Thyroid Gland). The Thymus is a small gland located within the chest cavity behind the breast bone. It is part of the body’s immune system programming groups of cells which produce antibodies to attack foreign invaders in the body. In the case of MG, the rogue antibodies which are against the acetylcholine receptors (AchR)at the nerve-muscle junction are confused and start attacking the body they are meant to protect. (autoimmune disease)

A few general observations here will help to reinforce the fact that MG is no longer regarded as a fatal disease. Incurable yes, but with the present treatment available it is quite manageable. It is not contagious, nor is the acquired form with AChR antibodies considered to be hereditary. It is known however that other siblings in a family have an increased risk of being diagnosed with MG. Given the low incidence of the disease the chances of siblings experiencing MG is still uncommon.

The maximum level of progression of the disease is usually known in the first few years after diagnosis. If it remains limited to ocular muscles (Ocular MG) for 2 years it is unlikely to spread to other muscles.

Your MG may be with you for your life, as remission occurs in only about 25% without treatment. Medical treatment to control the disease is often required to be taken life-long. (Just as in other conditions such as epilepsy or diabetes mellitus)

In the next chapter we will refer to the various treatments available depending upon the circumstances surrounding your diagnosis and your continuing symptoms.