Diagnosis and treatment of ocular myasthenia gravis with ptosis and diplopia

What is myasthenia gravis?

What is myasthenia gravis? When you experience muscle weakness and muscle fatigue, it is called myasthenia gravis.

In order for us to move our muscles, we need nerves that control them, so the nerves are attached to the muscles. And it gives you a command so that your muscles can move. This is the part where the nerves and muscles meet, so it's called the 'neuromuscular junction'. Myasthenia gravis is a disorder of this neuromuscular junction. When you have nerves, the nerve endings secrete a substance called acetylcholine. These substances bind to the receptors, or receptors, of acetylcholine in the muscles to give commands. When myasthenia gravis occurs, the receptors are broken. Patients with myasthenia gravis have a good amount of acetylcholine secreted, but their receptors are all broken down, and they lose their muscles. Normally, a 30% decrease in acetylcholine receptors can lead to this condition.

Myasthenia gravis?

Patients with myasthenia gravis may only have ptosis, which is drooping eyelids, but the majority of patients complain of double vision in addition to ptosis. In about 25% of cases, the strength of the muscles that close the eyes decreases, and the eyes open again even if the eyes are tightly closed.

So, what about the natural history of ocular myasthenia gravis? What's interesting is the 'Rule of Two'. About 1/2 of all myasthenia gravis patients do not come because they are weak, but because they have ptosis or double vision. In addition, 1/2 of patients with myasthenia gravis will have myasthenia gravis spread throughout the body if left untreated. This progression usually occurs within two years. Therefore, I can tell you that patients with myasthenia gravis who come to the ophthalmologist for the first time can rest assured that if it does not spread to the whole body for about two years and the medication is going well, there is no possibility of it spreading to the whole body.

Diagnostic methods for ocular myasthenia gravis

There is an electromyography test called 'EMG'. It's an electrical impulse around the peripheral muscles. When stimulated, you normally have to go back and forth above the threshold level, but in the case of myasthenia gravis, the response drops below the threshold level. In other words, myasthenia gravis means that the more stimulation you give, the more fatigue you get and the weaker your muscle strength becomes.

It is also tested with ice. If you put ice on it, your eyes may light up. We don't know what causes it yet, but we think that cold ice inhibits acetylcholinesterase enzymes. They are also tested after injecting a substance called pyridostigmine that inhibits the breakdown of acetcholine.

Finally, a CT scan of the chest may be done. CT scans of the chest show abnormalities in more than half of cases, or nearly 75% of cases.

How to treat myasthenia gravis]

Myasthenia gravis should be treated early and well. So what are the treatments? The most commonly used are acetylcholinesterase inhibitors. Drugs such as mestinone are the most basic.

Other drugs include steroids and immunosuppressants. They are known to help prevent damage to the neuromuscular junction and prevent myasthenia gravis from turning into a systemic one. And then there is thymectomy. The thymus gland is where the body's immune cells are trained. In particular, it is the thymus gland that plays an important role in the differentiation and training of T-cells. In this regard, in 1939, Dr. Blalock reported that the removal of the thymus gland in people with hypertrophia thymus improved myasthenia gravis, and in the 1990s, it was established as standard treatment to remove the thymus gland with thymoma in patients with generalized myasthenia gravis. In 2016, a study showed that patients with myasthenia gravis with acetylcholine receptor antibodies had less use of steroids and immunosuppressants and shortened hospital stays when they removed a normal thymus gland that did not have a problem with the thymus.

So, will this thymectomy also help with ocular myasthenia gravis, which is confined to the eye? There is no established understanding of whether or not thoracic resection is helpful for myasthenia gravis, which is limited to the eye, unlike generalized myasthenia gravis.

theorem

To sum up, myasthenia gravis is a disease in which acetylcholine receptors, the muscle receptors that receive the secretion of acetylcholine from nerves that control muscles, are damaged. As a result, the muscles get tired easily, which can lead to double vision, ptosis, which is the drooping of the eyelids, and a weakening of the ability to close the eyes. One of the characteristics is that these things are fine in the morning, but in the afternoon, they become more tired and have a fluctuating circadian routine.

Tests may include an ice test to see if the eyelids are raised, an electromyography test, and pyridostigmine to see if eye movement disorders improve. And then we do a blood test to see if we have positive antibodies to the acetylcholine receptor, and we do a CT scan of the chest to see if it's a thymoma, a thymus problem.

The first basic treatment is to use drugs such as pyridostigmine, an acetylcholinesterase inhibitor, and mestinone for commercial use. And to prevent myasthenia gravis in the eye from becoming systemic and to prevent receptor damage, steroids or immunosuppressants may be added.

Lastly, we can think of surgical treatment to remove the thymus gland. Myasthenia gravis may be considered when acetylcholinesterase receptor antibodies are positive and do not respond to conventional treatment, or when complications from drug-induced steroids or immunosuppressive drugs are severe. Thymectomy is the standard treatment for myasthenia gravis when there is an abnormality in the thymus gland or positive acetylcholine receptor antibodies, but the results for ocular myasthenia gravis have not yet been established.