Myasthenia Gravis and other Myasthenic syndromes


Myasthenia gravis (MG) is an autoimmune disease, usually caused by antibodies that attack the acetylcholine receptors or a protein called MuSK on voluntary muscle (muscle that we consciously use to move parts of our body). The acetylcholine receptors bind a chemical called acetylcholine, which is an essential message signal released from the nerve ending when we want to tell our muscles to move, for example when we need to walk or open our hand to pick up a pencil or a cup. The loss of these receptors reduces communication between the nerve and the muscle and causes muscle weakness with fatigue.

Of the other myasthenic syndromes, Lambert-Eaton Myasthenic syndrome (LEMS) is also an autoimmune disease, caused by antibodies directed at the calcium channels at the nerve terminal on which acetylcholine release is dependent. This results in a decrease in the amount of acetylcholine released by the nerve impulse.

In the congenital myasthenic syndromes (CMS) the immunological system is not involved at all. These are inherited genetic conditions in which mutations in a number of genes responsible for producing proteins (currently at least 12) at different sites at the neuromuscular junction interfere with the signals sent from the nerve to the muscle.

Most adults have the autoimmune form of the condition, whereas this is much less common in childhood. Consequently, CMS accounts for a relatively greater proportion of children with myasthenia than among adults.


Medical text written February 2010 by Doctor Stephanie Robb, Consultant Paediatric Neurologist, Dubowitz Neuromuscular Centre, Great Ormond Street Hospital, London, UK.

What are the symptoms?

MG is characterised by fluctuating weakness that becomes worse with increasing effort. Sometimes it affects only the eye muscles (ocular myasthenia) causing double vision and drooping of the eyelids. More commonly, the condition is generalised with weakness variously affecting not only the eye muscles but also the face, throat, neck, trunk, limbs and muscles that are involved in breathing. Some improvement in strength is achieved by rest.

Individuals with LEMS also have weakness of the legs and arms and there may also be disturbance of the autonomic nervous system, which can cause dry mouth and constipation. This type of MG is extremely rare in children.

CMS causes variable muscle weakness affecting the eyes, face, trunk, limb, breathing and swallowing muscles, which may be present from birth or develop in early childhood.

How is it treated?

MG usually responds at least partially to treatment with pyridostigmine by mouth, which prolongs the action of acetylcholine at the nerve-muscle junction and makes the muscles stronger. In more severe cases, treatment with steroids and/or other immunosuppressive medications such as azathioprine may be needed to reduce antibody production and improve muscle strength. In generalised MG with antibodies that attack the acetylcholine receptor, a thymectomy (an operation to remove the thymus gland, which is situated behind the breast bone) may help improve muscle strength. Thymectomy is not helpful in MG with MuSK antibodies, LEMS or CMS. LEMS is treated with 3, 4 diaminopyridine (DAP), which enhances acetylcholine release from nerve endings and/or other immunological treatments (not thymectomy). Some CMS respond well to pyridostigmine and 3,4 DAP. However, some subtypes of the condition are made worse by pyridostigmine, so it is important to have a precise genetic diagnosis before treatment, or for medication to be given for the first time in hospital.

Salbutamol (albuterol) or ephedrine may be helpful in these cases. Treatment with quinidine or fluoxetine is used for a subtype of CMS called the slow channel syndromes.

Adults and children with MG, LEMS and CMS are at risk of life-threatening swallowing and breathing difficulties, particularly with chest infections and should have fast-track access arranged to their local hospital. Temporary supportive care using a breathing machine and/or tube feeding may be needed to aid recovery. Those with repeated breathing problems should also be under the care of a specialist respiratory centre.

Inheritance patterns and prenatal diagnosis

Inheritance patterns
There is a very weak familial susceptibility to MG and to other autoimmune diseases in the families of patients with MG and LEMS. However all CMS are genetic disorders, most are autosomal recessive, apart from the slow channel syndromes, which are autosomal dominant. It is important to be referred to your regional genetics centre for further information if a CMS is diagnosed.

Prenatal diagnosis
This is not applicable to MG and LEMS. Prenatal diagnosis is now possible for CMS families, once the exact genetic fault is identified.

Is there support?

Myaware (Myasthenia Gravis Association)

Helpline: 01332 290 219
Email: [email protected]

The Association is a Registered Charity in England and Wales No. 1046443. It provides information and support to people affected by Myasthenia Gravis, Congenital Myasthenic Syndrome and Lambert Eaton Myasthenic Syndrome. Myaware Kids provides support for children with myasthenia and their parents and carers via its active Facebook group, and holds an annual weekend get-together. 

Group details last updated February 2016.

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