Do you often suffer from unexplainable muscle weakness? If yes, you may have myasthenia gravis (MG). According to the Myasthenia Gravis Foundation of America, the disorder, pronounced my-as-theen-ee-a grav-us, comes from the Greek and Latin words meaning “grave muscular weakness.” The organization further explains that “the most common form of MG is a chronic autoimmune neuromuscular disorder that is characterized by fluctuating weakness of the voluntary muscle groups. The prevalence of MG in the United States is estimated to be about 20/100,000 population. However, MG may be underdiagnosed and the prevalence may be higher.”
Unlike skin cancers that are more prevalent in white race, and brain tumors that affect more men than women, MG occurs in all races, both genders, and at any age. The disorder is not contagious, but it does occasionally happen in more than one member of the same family.
The Link Between Myasthenia Gravis and Cancer
Myasthenia gravis, especially at its late onset, carries a high risk for cancers outside of the thymus gland, according to a new study reported by Anna Pellisé, MD, from the Neurology Department at the Joan XXIII University Hospital in Tarragona, Spain.
MG is considered a paraneoplastic disease when accompanying thymoma, which affects up to 40% of patients who have thymoma, Dr. Pellisé said. Furthermore, patients with thymoma are at greater risk for a secondary malignancy whether or not they have MG. Myasthenia gravis by itself is a significant risk factor for extrathymic malignancies with or without the presence of thymoma. For example, a case report exclaims that myasthenia gravis is a presenting feature in a patient with lung cancer.
Older MG Patients at Risk for Extrathymic Neoplasms
Several studies have produced conflicting results regarding the prevalence of extrathymic malignancies in patients with MG. Between 2002 and 2012, Dr. Pellisé and her colleagues assessed the prevalence of extrathymic neoplasms. They compared the clinical characteristics and treatments of MG patients with or without extrathymic malignancies using a single-center retrospective chart. The focus group, comprising 38 patients diagnosed with MG, confirmed previous ones showing that old age is a significant factor in the elevated incidence of cancer in patients with MG. This includes men over 60 years of age, as well as women over 40 years of age.
Risk Factors of Myasthenia Gravis
Aside from age, researchers have found a connection between MG and the following factors:
1. Autoimmune Antibodies
The human body may form antibodies against acetylcholine receptors and destroy them. Acetylcholine receptors help nerve impulses enter the muscles, which gives them the energy required to function correctly. In the absence of acetylcholine, weakness will set in.
Antibodies produced by the immune system may also play a role in blocking a protein called tyrosine kinase, which the muscles need to ensure the neuromuscular junction works appropriately.
2. Tumors in the Thymus Gland
The thymus gland is found in the upper part of the chest. It is responsible for producing antibodies that fight viruses and infection. If a person suffers from an autoimmune disorder or genetic defect, the thymus gland can create antibodies that damage the acetylcholine receptors. Therefore, those with myasthenia gravis may have larger thymus glands or tumors in their bodies.
MG may also be caused by a genetic defect or a congenital syndrome, meaning there is a chance that children born to mothers with MG during pregnancy may have some of the antibodies. This may result in the baby exhibiting symptoms of MG for a few months after they are born.
Risk Factors that Precipitate Flares
The following may increase the chances of having a disease “flare”:
- Scorching temperatures
- Medications or antibiotics, including seizure drugs, anesthesia, and beta blockers.
Signs and Symptoms
Muscle weakness and fatigue are some of the primary symptoms of myasthenia gravis, which worsens over time, especially when the muscle is frequently used. Symptoms usually alleviate themselves with rest, meaning any muscle weakness may come and go. On the other hand, myasthenia gravis symptoms can also progress and reach their worst within a few years after the onset of the disease.
Although MG can affect any muscle that can be controlled voluntarily, specific muscle groups are more commonly affected than others, including:
1. Eye muscles
More than half the people with myasthenia gravis experience muscle weakness around their eyes. The first signs and symptoms involving eye problems are:
- Drooping of one or both eyelids, otherwise called ptosis.
- Double vision or diplopia, which improves or resolves itself when one eye is closed.
2. Face and throat muscles
Muscle weakness in the face and throat can cause:
- Difficulty swallowing. A patient with MG is prone to choking easily. This symptom makes it challenging to eat, drink, or take oral medication.
- Difficulty chewing. Muscles around the mouth may freeze halfway through a meal, mainly if the patient is eating something solid such as meats.
- Altered speaking. A patient’s manner of speech may sound very soft or nasal-like, depending on which muscles are affected.
- Limited facial expressions. If the muscles that control facial expressions are affected, an MG patient will find it hard to smile or show signs of emotion.
3. Neck and limb muscles
Myasthenia gravis may temporarily impair a person from moving due to muscle weakness in the neck, arms, and legs. This severe case of MG usually occurs along with muscle weakness in other parts of the body, including the eyes, face, or throat. If this muscle disorder affects the legs, a patient may waddle when walking or have difficulty standing altogether. If, on the other hand, the neck is concerned, it may become challenging to even hold the head up.
When properly treated, MG patients can remain physically active. Doctors use a variety of treatments, either alone or in combination, to relieve symptoms of myasthenia gravis. These treatments may include medications, intravenous therapy, surgery, and lifestyle changes.
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