Overview of Myasthenia Gravis

An autoimmune neuromuscular disorder that causes profound muscle weakness

In This Article

Myasthenia gravis is a condition that causes profound muscle weakness as a result of a person's immune system attacking receptors (docking sites) located on muscle tissue. The muscles in the eyelids and those attached to the eyeball are commonly the first (and sometimes only) muscles affected in myasthenia gravis. Other muscles that may become weak include jaw, limb, and even, breathing muscles.

Diagnosis of myasthenia gravis requires a thorough medical history and neurological examination, along with blood antibody test(s), electrodiagnostic studies, and imaging tests. While there is no cure yet for myasthenia gravis, the upside is that there are several therapies available to improve symptoms.

Cause

Myasthenia gravis occurs when antibodies, which are proteins produced by a person's immune system, misguidedly attack the receptors for acetylcholine—a chemical messenger released by nerve cells to stimulate muscle contractions. These antibodies are called acetylcholine receptor (AChR) antibodies and as a result of their interference with the transmission of nerve to muscle signaling, muscle weakness develops.

It's important to note that in some cases, instead of antibodies produced against acetylcholine receptors, a person with myasthenia gravis has antibodies produced against proteins located on the surface of the muscle membrane. These antibodies are called muscle-specific receptor tyrosine kinase (MuSK) antibodies.

Symptoms

The primary symptom of myasthenia gravis is significant, specific muscle weakness that tends to get progressively worse later in the day, especially if a person is using the affected muscles a lot.

A common first symptom of myasthenia gravis is droopy eyelids or "tired eyes" (called ptosis) and/or blurry or double vision (called diplopia).

While some people with MG only experience eye muscle weakness (called ocular myasthenia), other progress to a more generalized form of the disease, where multiple muscles are affected.

In those individuals, besides eye-related problems, these symptoms may occur:

  • Mouth/jaw weakness, leading to trouble chewing or swallowing food, or slurred speech
  • Limited facial expressions
  • Arms, hands, fingers, legs, and or neck weakness

Keep in mind, the "weakness" of myasthenia gravis is different than, for example, the tiredness someone might feel in his or her legs after standing or working all day. "Weakness" implies only barely being able to move a particular muscle.

Rarely, a myasthenic crisis may occur. This is a life-threatening condition, often triggered by a change in medication, infection, or surgery, that is characterized by difficulty breathing due to severe weakness of the respiratory muscles. Due to the severe shortness of breath, intubation (when a person is placed on a breathing machine) and monitoring in an intensive care unit are required.

Diagnosis

The diagnosis of myasthenia gravis begins with a medical history and neurological examination. Then, if symptoms and signs suggestive of myasthenia gravis are present, additional confirmatory tests will be performed (often by a neurologist).

Medical History and Neurological Exam

During the medical history, a doctor will listen carefully to your health story and ask you pertinent questions. For example, he may ask the following questions if he suspects myasthenia gravis based on your complaint of "tired or dropping eyes."

  • Are you having any difficulties speaking or swallowing?
  • Besides your eye weakness, are you experiencing weakness anywhere else in your body (e.g., arms or legs)?
  • Is your weakness worse in the morning or evening?

After these questions, your doctor will perform a neurological exam in which he evaluates your muscle strength and tone. He will also check your eyes to see if there are any problems with eye movement.

Blood Test(s)

In addition to a medical history and physical exam, if a person has symptoms suggestive of myasthenia gravis, there are antibody blood tests that can be done to confirm the diagnosis.

The most specific test is to check the blood for the presence of abnormal antibodies using the acetylcholine receptor antibody test. Presence of the antibodies confirms the diagnosis. Your doctor may also check for the presence of MuSK antibodies.

Electrophysiological Studies

Electrophysiological studies, such as repetitive nerve stimulation studies and single-fiber electromyography (EMG), can be very helpful in diagnosing myasthenia gravis, especially if other tests (like the antibody blood test) are normal, but a doctor's suspicion for MG is still high, based on a person's symptoms.

Edrophonium Test

The edrophonium test, also called the Tensilon test, has mostly fallen out of use due to the unavailability of the chemical used in the test (edrophonium).

Historically though, during this test, a doctor injects edrophonium—a medicine that prevents the breakdown of acetylcholine—into a vein. If muscle strength improves after this medicine is given, the test is considered positive and offers strong support for the diagnosis of MG.

Imaging Tests

Most people with myasthenia gravis have a tumor of the thymus gland—an immune system gland that is located in your chest. Imaging tests, usually a computed tomography (CT) scan or magnetic resonance imaging (MRI), can diagnose thymomas.

Keep in Mind

An MRI of the brain may also be ordered during the diagnostic process to evaluate for mimicking conditions like stroke, brain tumor, or multiple sclerosis.

Treatment

While there is no cure for myasthenia gravis, there are treatments that ease symptoms and calm the disease down.

Acetylcholine Inhibitors

Drugs called acetylcholinesterase inhibitors, which block the breakdown of acetylcholine, can help increases the levels of acetylcholine at the neuromuscular junction. The main acetylcholinesterase inhibitor used to treat myasthenia gravis is pyridostigmine (Mestinon).

Potential side effects of this drug include diarrhea, abdominal cramping, and nausea; although taking it with food can reduce these gastrointestinal effects.

Medications That Suppress the Immune System

Glucocorticoids, such as prednisone, are often used to suppress the abnormal production of antibodies in people with myasthenia gravis.

Other immune-system suppressing drugs sometimes used to treat myasthenia gravis include:

  • Imuran (azathioprine)
  • CellCept (mycophenolate mofetil)
  • Prograf (tacrolimus)
  • Rituxan (rituximab)

Important Note

Immunosuppressant medications require careful monitoring by your doctor, as they all may cause potentially serious side effects.

Plasmapheresis

Plasma exchange (plasmapheresis), in which the person's blood plasma containing the abnormal antibodies is removed and fresh plasma is put back in, is used to treat an acute myasthenic crisis. This procedure may also be done before surgery, which may trigger a myasthenic crisis.

The caveat about plasmapheresis is that while it works within days, the benefits are short-lived (usually just weeks). In addition, plasmapheresis is expensive and complications may arise, such as:

  • Heart arrhythmias
  • Low blood pressure
  • Bleeding
  • Muscle cramps

Intravenous Immunoglobulin

Intravenous immunoglobulin (IVIG) entails giving a person (through their vein) a high concentration of antibodies collected from healthy donors. The administration of IVIG is usually done over a period of two to five days. While possible side effects of IVIG are generally mild, serious complications may occur including kidney failure, meningitis, and allergic reactions.

Just like plasmapheresis, intravenous immunoglobulin (IVIG) may be used to treat a myasthenic crisis or administered prior to surgery. Also like plasmapheresis, the effects of IVIG are short-lived.

Thymectomy

Surgery to remove the thymus gland (called thymectomy) can reduce, and possibly even resolve, symptoms in people with myasthenia gravis.

While surgery is definitely indicated in people with a thymus gland tumor, whether thymectomy is indicated in other cases is less clear. In these instances, it's important to have a thoughtful discussion with a neurologist who has experience treating myasthenia gravis.

Prevention

A key strategy for preventing myasthenic attacks is to avoid/minimize possible triggers:

Potential triggers for myasthenic attacks include emotional stress, surgery, pregnancy, thyroid disease (underactive or overactive), and increases in body temperature. Certain medications can also trigger an attack, such as:

Important Note

Individuals with myasthenia gravis should be careful before starting any new medication and watch carefully after taking it for signs of muscle weakness.

Infection, such as with the flu or pneumonia, can also trigger a myasthenia flare. With that, be sure to obtain all recommended vaccines, such as your yearly flu shot.

A Word From Verywell

The future of myasthenia gravis is bright, as researchers work tirelessly to find therapies that target and perhaps fix or cure the immune system abnormality that lies at the crux of myasthenia gravis.

Until then, continue to remain active in your healthcare—see your doctor regularly, report any new symptoms right away, and take your medication as advised.

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