One type of myasthenia gravis (MG) is characterised by easily becoming tired and weakening of the muscles controlling the eyelids and movement of the eyes. Double vision, drooping eyelids, and/or ocular closure are common symptoms. About 15% of MG patients only experience eye issues. The initial signs of MG are frequently ocular, and many patients go on to experience different types of generalised muscular weakness in the future. A blood test can identify autoantibodies against acetylcholine receptors (AChR) in about 50% of patients with ocular myasthenia gravis.
One type of MG that causes widespread muscle weakness is called generalised myasthenia gravis. Ptosis, or droopy eyelids, can cause double vision and other symptoms. Other symptoms include breathing difficulties, speaking difficulties, chewing and swallowing difficulties, difficulty doing daily tasks, and generalised muscle weakness. Blood testing for acetylcholine receptor (AChR) autoantibodies are positive in about 85% of patients with MG.
The percentage of MG patients that test positive for anti-muscle-specific kinase (MuSK) antibodies is approximately 6%. Both AChR and MuSK antibodies can be found in extremely uncommon circumstances. The majority of patients with generalised myasthenia gravis test positive for MuSK antibodies.
Treatment decisions for MG patients may be influenced by the quantity and kind of antibodies found in their blood. Individuals with AChR antibodies may react to drugs differently from those with anti-MuSK antibodies.
When anti-AChR and anti-MuSK autoantibodies are not detectable in the blood, a person with ocular or generalised myasthenia gravis is said to have seronegative myasthenia gravis. Similarities between patients with AChR and MuSK antibodies frequently exist in terms of symptoms and therapy response. To confirm an MG diagnosis, specialised diagnostic tests could be necessary (for more information, visit the Seronegative Resource Centre).
About 10% of MG patients are thought to be seronegative. Antibodies for other proteins, including agrin or LRP4 antibodies, can occasionally be found, indicating that these autoantibodies may be MG indicators. Fewer patients will probably be classed as seronegative when more recent MG antibodies are found.
Study up on seronegative MG.
Find out more about the various forms of MG.
Congenital myasthenic syndromes (CMS): This is the term used to describe a collection of rare, inherited neuromuscular junction illnesses. A genetic mutation in a particular protein component of the neuromuscular junction causes a variety of CMS forms. In individuals with suspected CMS, a comprehensive diagnostic examination is valuable due to the variety of forms and available treatments.
And what distinguishes autoimmune MG from CMS?
Not as common as autoimmune MG is CMS.
CMS typically appears early in life, frequently during infancy.
Generalised weakness and exhaustion are typical lifetime and/or relatively stable CMS symptoms, with fewer and less severe exacerbations.
Antibodies directed against the neuromuscular junction’s components are not linked to CMS.
Genetic mutations in neuromuscular junction components cause all CMS diseases.
Immunotherapies are not necessary for CMS symptoms.
Transient neonatal myasthenia: 10–15% of babies born to mothers with autoimmune MG develop this illness. Neonatal myasthenia is a transitory condition caused by maternal antibodies that cross the placenta in late pregnancy. A feeble cry or suck and widespread weakness at birth are among the symptoms. The symptoms go away over the course of a few weeks as the mother’s antibodies break down in the infant’s body. There is no longer a risk of long-term or future myasthenia gravis in infants with transient neonatal MG.
See Andrew G. Engel, MD’s information for additional details, provided by the National Organisation for Rare Disorders.
Myasthenic syndrome of Lambert-Eaton (LEMS)*: This is an additional autoimmune condition when the body’s own neuromuscular junction is attacked by the immune system. LEMS is brought on by autoimmune attacks to the nerve aspect of the neuromuscular junction, which interfere with nerve cells’ capacity to communicate with muscle fibres. This is distinct from autoimmune MG, which is brought on by attacks to the muscle portion of the neuromuscular junction.
Two types of LEMS exist:
One kind has an older age of onset and is linked to small cell lung cancer in 50–60% of cases.
The other kind, which accounts for 40–50% of cases, begins at a younger age and is unrelated to cancer.