Myasthenia gravis: Year of the Zebra 2024

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Myasthenia gravis is an autoimmune disorder that causes weakness in skeletal muscles. It occurs when the body mistakenly produces antibodies that attack the neuromuscular junction, which is the meeting point between nerve endings and muscle fibers.
Typically, when the brain sends a signal to move a muscle, it travels down motor nerves until it reaches the neuromuscular junction.
At this junction, nerve cells release a chemical messenger called acetylcholine, a neurotransmitter which crosses a small gap and binds to receptors on the surface of muscle cells, triggering muscle contraction.
With myasthenia gravis, antibodies bind to these receptors, blocking their interaction with acetylcholine and weakening muscle contraction.
Over time, these antibodies can damage and reduce the amount of receptors on the muscle cell surface, further leading to weak and easily fatigued muscles.
Although it is unclear why, myasthenia gravis tends to affect young females in their twenties and thirties and older males in their sixties and seventies.
It is also more common in people who have a thymoma, which is a type of tumor that develops in the thymus gland. The hallmark symptom of myasthenia gravis is muscle weakness that worsens after activity and improves with rest.
Initially, myasthenia gravis may only affect the muscles that control movement of the eye and eyelids, causing symptoms like double vision or drooping eyelids.
When the arm and leg muscles are involved, people might experience severe fatigue and difficulties with walking or climbing stairs.
Weakness in the muscles responsible for swallowing and speech production can cause symptoms like a change in voice and slurred speech, as well as difficulty swallowing.
Finally, if the muscles that control breathing are affected, people can develop a myasthenic crisis, which is a life-threatening manifestation of the disorder that causes muscle weakness of the respiratory muscles, leading to difficulty breathing which rapidly results in respiratory failure if not treated.
Some factors that may trigger a myasthenic crisis include infections, surgery, medications, or even stress. Diagnosis is usually based on suggestive symptoms and the presence of the anti-acetylcholine receptor antibodies in the blood.
A simple bedside test that can assist in the diagnosis is the ice pack test, which involves placing an ice cube over the person’s eyelids for a couple of minutes and then checking if there is an improvement in muscle strength.
The cooling effect of the ice pack temporarily slows the breakdown of acetylcholine, which can improve muscle weakness in people with myasthenia gravis.
Additional tests may include electromyography and nerve conduction studies, which typically show decreased muscle activity with repetitive stimulation.
Once myasthenia gravis is diagnosed, a CT scan or MRI of the thorax may be done to check for thymoma. Treatment of myasthenia gravis consists of medications that increase the amount of acetylcholine available to muscle cells, like neostigmine or pyridostigmine.
Severe cases can also be treated with immunosuppressive medications, like prednisone, which reduce the production of harmful antibodies.
Finally, many individuals with myasthenia gravis undergo surgical removal of the thymus, which can improve symptoms even in those that don’t appear to have any issue with the thymus gland itself.
Alright, as a quick recap… Myasthenia gravis is an autoimmune disorder caused by antibodies against the neuromuscular junction.
It is clinically characterized by muscle weakness that worsens with activity and improves with rest. The purpose of treatment is to reduce the immune system's attack on the muscles and improve muscle strength by increasing the amount of acetylcholine available around muscle cells.
Myasthenia gravis: Year of the Zebra: Video | Osmosis