What is Myasthenia Gravis?
Myasthenia gravis (MG) is a chronic autoimmune disorder characterized by weakness and fatigue of voluntary muscles. It results from an abnormal immune response in which the body’s immune system mistakenly targets the neuromuscular junction—the specialized connection between nerves and muscles. This leads to impaired communication between the nerves and muscles, resulting in muscle weakness and fatigue that worsens with activity and improves with rest.
Causes & Symptoms
The primary underlying cause of myasthenia gravis is the production of autoantibodies, specifically antibodies called acetylcholine receptor antibodies (AChR antibodies) or, in some cases, muscle-specific kinase (MuSK) antibodies. These antibodies target and bind to the acetylcholine receptors at the neuromuscular junction, interfering with the normal transmission of nerve impulses to the muscles. As a result, the muscles receive fewer signals, leading to weakness and fatigue.
Myasthenia gravis can affect individuals of any age, but it is more commonly diagnosed in young adult women and older men. The specific symptoms and the muscles affected can vary widely among individuals. Common manifestations include weakness and fatigue in the muscles controlling eye movement, facial expression, swallowing, and limb movement. Double vision (diplopia), drooping of the eyelids (ptosis), difficulties in chewing and swallowing, and weakness in the arms and legs are often observed.
The Neuromuscular Junction is a Gap Between the Ends of Nerves and Muscles
Nerves release a chemical called acetylcholine, which then attaches to muscles and starts a series of chemical and electrical reactions that make the muscle contract. There are a number of conditions that interfere with this communication and process, the most common being myasthenia gravis.
Myasthenia gravis is a neuromuscular junction disorder in which an individual’s immune system makes antibodies (immune proteins) that block acetylcholine from binding onto muscles, making it harder for muscles to contract.
- This causes intermittent weakness, especially with sustained muscle use and later in the day.
- It tends to have the most effect on muscles that have to work continuously, such as eyelids, neck muscles, and thighs, so patients may experience double vision, droopy eyelids, and leg heaviness.
- If the disorder affects the whole body, it is called generalized myasthenia.
- In some instances, myasthenia only affects muscles in the head (bulbar myasthenia), causing eyelid droopiness (ptosis), difficulty swallowing (dysphagia) and double vision (diplopia).
- The neurologist will perform a detailed history exploring symptoms, other medical problems, medications, and family history.
- This is followed by an examination of the nerves and muscles by asking the patient to perform a number of tasks, such as looking up at a target for 30-60 seconds and checking strength of muscles in your arms and legs.
- If there is suspicion for myasthenia gravis or associated conditions, we order blood tests for myasthenia antibodies. However, in many cases of myasthenia the blood tests are negative.
- In those instances, specialized nerve conduction studies (repetitive stimulation) can be helpful.
- If those are negative, specialized needle electromyography (EMG) testing called single fiber EMG is often performed to measure the electrical activity in the muscle.
- Additionally, many individuals with myasthenia have residual thymus (a gland in the chest that usually shrinks away during young adulthood), so we will usually order a chest scan (MRI or CT).
One of the most important points in management is to avoid medications that can worsen myasthenia.
In individuals with myasthenia, symptoms are usually manageable with a medication called pyridostigmine which increases the amount of acetylcholine available to muscles and helps overcome the fatigue and weakness.
While pyridostigmine can be very effective at reducing symptoms from myasthenia, it does not treat the underlying disorder.
For treatment of the underlying condition in patients who need rapid relief from bothersome symptoms, physicians can order IV gamma globulin infusions or, less commonly, a blood-filtering process (plasmapheresis) which is similar to dialysis.
For long term management, many patients need immunosuppressants (medications that reduce immune activity), such as prednisone, azathioprine, and mycophenolate.
Myasthenia Gravis Care Team
The specialist at the Pacific Brain Health Center in California are trained experts ready to evaluate and treat you, helping you to stay involved with the activities and people who matter to you.
We offer convenient access to specialists who can provide kind, thorough clinical evaluations including EMG/NCS tests (electromyogram and nerve conduction studies), and infusion therapies. Pacific Neuroscience Institute also offers speech and language pathology services for patients with myasthenia gravis.