Myasthenia gravis (MG) is a chronic, autoimmune disorder caused by a breakdown in the communication between nerve endings and muscles in the neuromuscular junction. At the junction, the nerve ending and muscle communicate via a neurotransmitter known as acetylcholine.
In MG, antibodies block or destroy receptors at the junction, affecting signal transmission. This results in muscle fatigue and weakness.
Ocular MG: Affects only the eye muscles, causing intermittent drooping eyelids and double vision. It may remain localised to the eye muscles, or progress to generalised MG.
Generalised MG: Involves muscles beyond the eyes, including those used for breathing, swallowing and limb movement.
Early-onset: Before age 50, more common in females, and often linked to an enlarged thymus
Late-onset: After age 50, more common in males
Thymoma-associated: Linked to thymic tumours (around 10-15% of cases)
Congenital myasthenic syndromes (CMS): Inherited, non-autoimmune form present from birth.
Transient neonatal MG: Temporary weakness in newborns of mothers with MG, resolving after birth.
Seronegative MG: No detectable antibodies but similar symptoms; diagnosed clinically.
MG affects voluntary muscles in the body. Weakness may come and go, become more prominent as the affected muscle is used repeatedly, and improves with rest.
Signs may be generalised or localised:
Common signs include:
Not all signs occur at the same time or are always present. The signs usually occur slowly but may develop acutely with generalised weakness and rapid weakening of swallowing and breathing muscles. This is termed myasthenic crisis and needs immediate medical attention.
There is currently no known way to prevent myasthenia gravis as it is an autoimmune condition with unclear causes. However, for patients with MG, managing triggers and risk factors can help reduce symptom severity and prevent flare-ups. This includes taking medications as prescribed, avoiding infections, reducing stress and avoiding certain drugs that can worsen muscle weakness.
The exact cause of myasthenia gravis is not fully understood, but abnormalities in the thymus gland are often implicated. In many cases, the thymus, which plays a role in immune system development, is found to be unusually large (thymic hyperplasia) or may have a tumour (thymoma).
MG affects all ages, sex and ethnic groups. It is most common in young adult women under 40 and older men over 60. It may affect newborns when a mother with MG passes the abnormal antibodies to the foetus. In adults, it is usually not hereditary. MG is not contagious.
A consult with a neurologist is needed to confirm the diagnosis. Tests include:
Blood tests: To detect antibodies (e.g. anti-acetylcholine receptor antibodies) that are abnormally high in MG.
Repetitive nerve stimulation (RNS): Small, safe and tolerable electric currents are delivered to nerves in quick succession to check nerve responses and function.
Single fiber electromyography (SFEMG): A small needle electrode is inserted into the muscles to record differences in response time between muscle fibres.
Computed tomography (CT) scan: Approximately 10-15% of patients with MG have an associated thymoma, a tumour of the thymus. The thymus is a gland in the chest that is involved in the immune system. A chest CT scan may be needed to check for a thymoma. Most of these thymomas are not malignant.
With proper treatment, signs and symptoms of MG can be relieved and normal daily function achieved.
Intravenous immune globulin (IVIG) treatment
Immunoglobulins are derived from donated blood and contain normal antibodies that temporarily counteract the abnormal antibodies in the body.
Plasma exchange (plasmapheresis)
Abnormal antibodies are filtered out of the body by a machine, similar to the concept of dialysis. IVIG or plasmapheresis is used in acute cases.
Medications
Medication such as pyridostigmine is prescribed to improve muscle weakness by increasing the amount of neurotransmitters (acetylcholine) in the neuromuscular junction. Common side effects include increased phlegm, diarrhoea and abdominal discomfort.
Immunosuppressant such as steroid is prescribed to suppress the immune system. Side effects include weight gain, water retention, acne, hypertension, diabetes, infections, gastric ulcers, osteoporosis and cataracts. These side effects can be minimised with diet modications and medications.
The above list is not exhaustive and you should discuss these treatment options further with your doctor.
Surgery In certain instances (e.g. thymoma), removal of the thymus gland is necessary.
The initial signs of myasthenia gravis usually include muscle weakness that worsens with activity and improves with rest. Common symptoms are drooping eyelids, double vision, difficulty swallowing or speaking and general fatigue. Some people may also notice weakness in the arms or legs.
A diagnosis of myasthenia gravis is often prompted by symptoms of intermittent fatigue in the arms, legs, eyes or breathing muscles. Doctors will usually perform a range of tests, including blood tests to detect antibodies, electromyography (EMG) to assess muscle response and imaging scans to check the thymus gland for abnormalities.
Although myasthenia gravis cannot be cured, it can be managed. Treatment focuses on controlling symptoms and improving muscle strength, often with medications like acetylcholinesterase inhibitors, immunosuppressants or surgery to remove the thymus. With proper care, many people with MG can lead relatively normal lives.
Download the Myasthenia Gravis brochure.
Myasthenia gravis - symptoms, causes, treatment: Nord. National Organization for Rare Disorders. (2024, October 1). https://rarediseases.org/rare-diseases/myasthenia-gravis/
Myasthenia Gravis (MG) - diseases. Muscular Dystrophy Association. (2024, June 3). https://www.mda.org/disease/myasthenia-gravis
U.S. Department of Health and Human Services. (n.d.). Myasthenia Gravis. National Institute of Neurological Disorders and Stroke. https://www.ninds.nih.gov/health-information/disorders/myasthenia-gravis
Suresh, A. B. (2023, August 8). Myasthenia Gravis. StatPearls [Internet]. https://www.ncbi.nlm.nih.gov/books/NBK559331/
Home. Myasthenia Gravis Foundation of America. (2024, October 1). https://myasthenia.org/
De Baets, M. h., & Kuks, J. b. (2019). Immunopathology of myasthenia gravis. Myasthenia Gravis, 147–202. https://doi.org/10.1201/9780429276750-5
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