Myasthenia gravis

Overview

An autoimmune condition called myasthenia gravis (MG) causes any muscles that are controlled by the voluntary system to weaken and quickly tire. It results from a breakdown in the regular connection between the nerves and muscles (neuromuscular junction.

Myasthenia gravis can be classified into two main types:

• Ocular: In this type, the muscles responsible for eye movement and eyelid control become weakened. Symptoms may include drooping eyelids, difficulty keeping the eyes open, and double vision. Ocular weakness is often the initial indication of myasthenia gravis. It’s worth noting that around half of individuals with ocular myasthenia gravis eventually progress to the generalized form within two years of experiencing the first symptom.
• Generalized: In this type, muscle weakness extends beyond the eyes and affects various other parts of the body, such as the face, neck, arms, legs, and throat. Individuals with generalized MG may experience difficulties in speaking, swallowing, raising their arms, getting up from a seated position, walking long distances, and climbing stairs.

While there is currently no cure for myasthenia gravis, various treatments are available to alleviate the signs and symptoms.

Symptoms

Myasthenia gravis (MG) typically manifests with abrupt onset of initial symptoms. This neuromuscular disorder leads to muscle weakness during periods of activity, which improves upon resting. However, over time, the symptoms of MG generally worsen, often peaking within a few years following the disease’s onset. While myasthenia gravis can impact any voluntarily controlled muscles, specific muscle groups are more frequently affected than others.
Face and throat muscles
In approximately 15% of individuals with myasthenia gravis, initial symptoms manifest in the muscles of the face and throat, resulting in various effects. These can include impaired speech, characterized by a soft or nasal quality depending on the affected muscles, as well as difficulties in swallowing, leading to easy choking and challenges with consuming food, liquids, or medication, with potential leakage through the nose. Chewing can also be affected, with the involved muscles becoming fatigued during a meal, particularly when faced with harder food items like steak. Additionally, facial expressions may undergo changes, such as a smile resembling a snarl.
Neck and limb muscles
Myasthenia gravis can result in weakened neck, arm, and leg muscles, affecting mobility and posture. The weakness in the legs can impact one’s ability to walk, while the weakened neck muscles make it difficult to maintain head support.
Eye muscles
Myasthenia gravis often presents with initial symptoms related to the eyes in over 50% of affected individuals. These symptoms commonly include drooping of one or both eyelids, known as ptosis, as well as double vision (diplopia). The double vision may appear horizontally or vertically and typically improves or goes away when one eye is closed.

If you experience any difficulties with breathing, seeing, swallowing, chewing, walking, using your arms or hands, or holding up your head, it is important to consult with a doctor. These symptoms could indicate underlying health issues that require medical attention. Seeking professional advice will help diagnose the problem and ensure appropriate treatment is provided to address your specific concerns.

Causes

Myasthenia gravis is an autoimmune condition. The immune system of the body attacks itself for unknown causes.

• Antibodies: Myasthenia gravis is a condition where the immune system produces antibodies that interfere with the normal functioning of the nerve-muscle junction. This junction relies on the release of acetylcholine, a neurotransmitter that binds to receptor sites on muscle cells. However, in myasthenia gravis, antibodies block or destroy many of these receptor sites, reducing the number of signals transmitted from nerves to muscles. As a result, muscle weakness occurs. Additionally, antibodies can target proteins such as muscle-specific receptor tyrosine kinase (MuSK) and lipoprotein-related protein 4 (LRP4), which are involved in the formation of the nerve-muscle junction. These antibodies can contribute to the development of myasthenia gravis. However, some individuals with myasthenia gravis do not have detectable antibodies against acetylcholine, MuSK, or LRP4. This type of myasthenia gravis is known as seronegative or antibody-negative myasthenia gravis. Although the specific antibodies involved in these cases are not yet identified, researchers believe that seronegative myasthenia gravis still has an autoimmune basis.
• Thymus gland: The thymus gland, located in the upper chest beneath the breastbone, is a part of the immune system. It is believed that the thymus gland plays a role in initiating or sustaining the production of antibodies that block acetylcholine. While the thymus gland is typically small in healthy adults, it can be enlarged in certain individuals with myasthenia gravis. Additionally, some individuals with myasthenia gravis may also develop thymomas, which are tumors of the thymus gland. Although thymomas are usually noncancerous (benign), there is a possibility for them to become cancerous (malignant).
• Other causes: Occasionally, mothers with myasthenia gravis may give birth to infants who also develop myasthenia gravis, known as neonatal myasthenia gravis. However, when promptly treated, these children typically experience recovery within two months of their birth. There is also a less common type of myasthenia gravis called congenital myasthenic syndrome, which is hereditary and present at birth.

Risk factors

The following factors increases the risk in developing Myasthenia gravis.

• Age. MG primarily impacts women between the ages of 20 and 40, as well as men between 50 and 80. Teenagers account for approximately 10% of MG cases, known as juvenile MG. Although MG can affect individuals of all ages, it is uncommon among children.
• History of other autoimmune diseases, such as rheumatoid arthritis and lupus
• Infections.
• Medications for malaria, heart arrythmias and cancer.
• Surgical procedures.
• Thyroid disease.