Myasthenia Gravis

Myasthenia gravis, or severe myasthenia, is an autoimmune disease in which the body attacks the structures where the nervous system and muscles meet (neuromuscular junction), specifically, the acetylcholine receptors. As a result of the incorrect functioning of neurotransmitters, the movement of voluntary muscles (those that require a signal to activate) becomes difficult.

Depending on how it manifests, there are two types of severe myasthenia:

• Generalized Myasthenia Gravis: Affects the entire body and usually presents after the age of 60. It typically hinders facial, respiratory, chewing movements, or those involved in speech. If it leads to a myasthenic crisis where breathing becomes impossible, it can cause death.
• Ocular Myasthenia Gravis: The most common form, which occurs before the age of 40. It affects the eyelids, causing ptosis, and the muscles controlling eye movement, leading to nystagmus (involuntary rapid eye movement).

Since it is a condition caused by an immune system disorder, myasthenia gravis is chronic and has no cure. However, there are treatments to alleviate symptoms and slow its progression.

In most cases, when medical recommendations are followed, patients with myasthenia gravis can live a normal life, and their life expectancy is not reduced.

Symptoms

Symptoms vary depending on the type of myasthenia gravis. The most characteristic ones are:

• Generalized Myasthenia Gravis:
• Muscle weakness
• Muscle fatigue that improves with rest
• Loss of strength
• Dysarthria (difficulty speaking)
• Dysphagia (difficulty swallowing)
• Dyspnea (breathing difficulties)
• Difficulty chewing
• Facial or body asymmetry
• Gait disturbance
• Death from myasthenic crisis (inability to breathe)
• Ocular Myasthenia Gravis:
• Ptosis (drooping eyelids), which affects both eyes but not symmetrically
• Diplopia (double vision)
• Nystagmus (involuntary, repetitive eye movements), which may be vertical, horizontal, or circular

Causes

The primary cause of myasthenia gravis is the presence of specific antibodies that attack the muscle tissue.

Additionally, it may be related to abnormalities in the thymus, an organ located under the sternum responsible for producing white blood cells. This gland is large at birth and shrinks over time, but some patients with myasthenia gravis have an abnormally enlarged thymus or present with thymomas (benign tumors).

Although it occasionally appears in several generations within the same family, myasthenia gravis is not hereditary. However, there is a genetic predisposition to developing autoimmune diseases.

Risk Factors

Myasthenia gravis is a rare disease that can occur in any person, though the following factors may increase the risk of developing it:

• Being over 60 years old: generalized myasthenia gravis is more common in older individuals.
• Being a woman under 40 years old: ocular myasthenia gravis is more frequent in younger women.

Complications

The most common complication of severe myasthenia is difficulty moving, speaking, swallowing, chewing, or breathing. As it affects respiratory muscles, it can lead to dyspnea and acute respiratory failure, potentially requiring hospitalization. This condition is known as myasthenic crisis and can be fatal.

Prevention

There is no known way to prevent myasthenia gravis.

Which doctor treats myasthenia gravis?

Neurologists and neurophysiologists are responsible for diagnosing and treating myasthenia gravis.

After analyzing the symptoms reported by the patient, the following tests are conducted to confirm the diagnosis:

• Blood tests to determine antibodies generated to destroy muscle movement receptors, the most common being anti-acetylcholine receptor antibodies.
• Electrophysiological studies: these are more revealing for detecting myasthenia gravis. Two main tests are conducted:
• Repetitive nerve stimulation to check if it can send signals to the muscle.
• Single-fiber electromyography to measure electrical activity between the muscle and the brain.
• Neurological examination: tests muscle strength and tone, reflexes, coordination, and balance, among other capabilities.
• Imaging tests to examine the state of the thymus.