What is myasthenia?
Acquired myasthenia is an autoimmune disease of the neuromuscular junction. It is characterised by a susceptibility to tiredness and muscle weakness. It is quite rare, affecting approximately 5 people in 100,000. Myasthenia can occur at any age but often affects older people of more than 50 years old and slightly more often it affects women than men.
Symptoms of myasthenia
The main clinical sign specific to myasthenia is muscle weakness. It increases considerably during activites which require effort or repeated movement. A long period of rest is then needed to return back to normal. This muscle tiredness can affect several muscles, especially those in the face: eyelids, cheeks, palate, muscles used for chewing or swallowing. Myasthenia can lead to several complications like problems swallowing or serious respiratory problems.
Types of myasthenia
We can distinguish between different forms of myasthenia depending on the function or the muscles affected by the disease.
- Ocular myasthenia: This disease affects the eye muscles. It is expressed by eye problems (double vision, drooping upper eyelids).
- Bulbar myasthenia: This concerns the muscles in the throat and face and can lead to false food routes. - General myasthenia: This form affects all of the muscles in the body, especially the shoulders, hips and neck. It commonly attributes a difficulty to remain stood up for a long time, or raise the arms.
Causes of myasthenia
Like every autoimmune illness, myasthenia is caused by a malfunction of the immune system against its own body. Autoimmune reactions are aimed against the componants of the neuromuscular junction, the motor plate between the nerve and muscle.
Abnormal antibodies attack the acetylcholine receptors, a neurotransmitter which communicates nervous signals to the muscles and release muscle contractions. The deterioration of these receptors prevents the communication of these nervous signals. This is what causes muscles to rapidly waste away. The precise causes of this autoimmune reaction are still virtually unknown. However a link has been detected with the thymus gland, a lymphatic organ found in front of the gap behind the sternum which produces these immune cells. In fact, researchers have shown that in more than ¾ cases of myasthenia, the thymus is abnormal. It is either underdeveloped or develops a tumour.
Myasthenia experiences varying degrees of development depending on the individual. However medical treatment, as well as regular monitoring, allows the majority of affected people to live almost normally. The aim of dealing with myasthenia is first and foremost to improve the function of the neuromuscular unction with the help of anticholinergics. Then corticoids and immunoregulatory drugs will help limit the autoimmune reaction. When myasthenia is caused by a thymus problem, its surgical removal, called thymectomy, can be vital. Also in around 15% of cases, it happens where myasthenia stops by itself.