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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.
Diagnosis
A physical examination and review of the patient’s symptoms will be performed by the healthcare provider. They could conduct a variety of tests, such as:
- Neurological examination: An examination of reflexes, muscle strength, muscle tone, senses of touch and sight, coordination, and balance are some of the neurological processes that a healthcare provider may use to determine neurological health.
- Imaging test: To screen for a tumor or other abnormality in the thymus, a healthcare provider may request a computed tomography (CT) scan or a magnetic resonance imaging (MRI).
- Electromyography (EMG): This test evaluates the electrical signals passing between your brain and muscles. It requires the insertion of a thin wire electrode through your skin into a muscle to examine the activity of a single muscle fiber.
- Ice pack test: In cases of a droopy eyelid, a common approach used by doctors is the application of an ice-filled bag on the affected eyelid. After a duration of approximately two minutes, the bag is removed, and the doctor carefully evaluates the eyelid for any noticeable signs of improvement.
- Blood analysis: A majority of individuals with MG exhibit elevated levels of acetylcholine receptor antibodies in their bloodstream, accounting for around 85% of cases. About 6% of patients with MG possess muscle-specific kinase (MuSK) antibodies. It should be noted that antibodies may not be detectable in less than 10% of individuals diagnosed with MG.
- Repetitive nerve stimulation: During a nerve conduction study for diagnosing myasthenia gravis, medical professionals apply electrodes to the skin above the targeted muscles. By administering small electrical pulses through these electrodes, they assess the nerve’s capacity to transmit signals to the muscles. Through repetitive testing, doctors observe if the nerve’s signal transmission deteriorates with fatigue, which aids in the diagnosis of myasthenia gravis.
- Pulmonary function tests: These tests assess if your breathing is being impacted by your condition.
Treatment
Treatment options for myasthenia gravis include a range of approaches that can be used individually or in combination. The choice of treatment depends on factors such as your age, the severity of your condition, and the rate of its progression.
- Medications
- Cholinesterase inhibitors: Pyridostigmine (Mestinon, Regonal) is a medication that enhances the communication between nerves and muscles, leading to improved muscle contraction and strength for certain individuals. While it is not a curative treatment, it can be beneficial. However, potential side effects may include gastrointestinal discomfort, diarrhea, nausea, as well as increased salivation and sweating.
- Corticosteroids: Prednisone is a type of corticosteroid that works by suppressing the immune system, thereby reducing antibody production. Although it can be effective, prolonged usage of corticosteroids carries the risk of significant side effects. These include bone thinning, weight gain, the potential development of diabetes, and an increased susceptibility to certain infections.
- Immunosuppressants: In addition to corticosteroids, doctors may prescribe medications such as azathioprine, mycophenolate mofetil, cyclosporine, methotrexate, or tacrolimus to modify the immune system. These immunosuppressants, although they may require several months to take effect, can have significant side effects including a heightened susceptibility to infections as well as potential damage to the liver or kidneys.
- Intravenous therapy: The following treatments are typically used in the short term to alleviate a rapid worsening of symptoms prior to surgery or other treatments.
- Plasmapheresis: This procedure employs a dialysis-like filtering process where your blood is directed through a machine to eliminate antibodies that hinder the transmission of signals between your nerve endings and muscle receptors. Nonetheless, the positive outcomes are typically temporary, lasting only a few weeks, and undergoing multiple treatments can pose challenges in accessing veins for the procedure. Plasmapheresis carries risks such as a decrease in blood pressure, bleeding, irregular heart rhythms, or muscle cramps. Additionally, certain individuals may experience allergic reactions to the solutions used as plasma replacements.
- Intravenous immunoglobulin (IVIg): The immune system’s reaction is changed by this therapy’s supplying the body with healthy antibodies. Benefits might last between three and six weeks and are usually seen in less than a week.
- Monoclonal antibody: Rituximab and eculizumab are intravenous medications utilized in the treatment of myasthenia gravis. Typically reserved for individuals who have not responded to alternative therapies, these drugs may produce significant side effects.
- Surgery:
- Myasthenia gravis patients may have a thymoma tumor in their thymus gland, which can be surgically removed through a procedure called thymectomy. However, even without a tumor, thymectomy can still potentially improve symptoms of myasthenia gravis, although it may take several years to see the benefits. Thymectomy can be performed either as an open surgery, where the sternum is split to access and remove the thymus gland, or as a minimally invasive procedure.
Minimally invasive surgery, aimed at removing the thymus gland, utilizes smaller incisions and may incorporate the following techniques:
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- Video-assisted thymectomy: During a specific type of surgical procedure, a small cut is made either in the neck or a few minor incisions are created on the side of the chest. Subsequently, surgeons employ a slender camera known as a video endoscope, along with tiny instruments, to visualize and extract the thymus gland.
- Robot-assisted thymectomy: During this type of thymectomy, surgeons utilize a robotic system comprising a camera arm and mechanical arms. The procedure involves creating multiple small incisions on the side of the chest and using the robotic system to extract the thymus gland.
