What is myasthenia gravis?

Voluntary muscles include muscles that connect to a person’s bones, muscles in the face, throat, and diaphragm. They contract to move the arms and legs and are essential for breathing, swallowing and facial movements. Myasthenia gravis is an autoimmune disease, which means that the body’s defense system mistakenly attacks healthy cells or proteins needed for normal functioning.

The onset of the disorder may be sudden. Symptoms may not be immediately recognized as myasthenia gravis. The degree of muscle weakness involved varies greatly among individuals.

Sometimes the muscles that control breathing weaken to the point where a person needs a ventilator to breathe. This is called a myasthenic crisis and requires immediate emergency medical care. A myasthenic crisis may be triggered by infection, stress, surgery, or an adverse reaction to medication. Approximately 15-20% of people with myasthenia gravis experience at least one myasthenic crisis and up to 50% of those may not be able to identify a trigger for their myasthenic crisis.

Who is more likely to get myasthenia gravis?

Myasthenia gravis affects both men and women and occurs across all racial and ethnic groups. It most commonly impacts young adult women (under 40) and older men (over 60), but it can occur at any age, including childhood. Myasthenia gravis is not inherited or contagious. Occasionally, the disease may occur in more than one member of the same family.

Myasthenia in children and infants

Although myasthenia gravis is rarely seen in infants, in a condition called neonatal myasthenia the fetus may acquire antibodies from the mother. Neonatal myasthenia gravis is generally temporary, and the child's symptoms usually disappear within two to three months after birth.

Rarely, children of healthy parents may develop congenital myasthenia. This is not an autoimmune disorder but is caused by mutations in genes required for normal function of the neuromuscular junction (the place where nerve cells connect with the muscles they control) and can cause similar symptoms to myasthenia gravis.

Scientists supported by NINDS are studying congenital myasthenic syndromes to improve diagnosis, treatment, and prevention, including developing targeted gene therapy for treating the disorders.

Causes of myasthenia gravis

Myasthenia gravis is caused by an error in how nerve signals are sent to muscles, specifically when communication between the nerve and muscle is interrupted at the neuromuscular junction.

Neurotransmitters are chemicals that neurons, or brain cells, use to communicate. When electrical signals or impulses travel down a nerve responsible for triggering movement in the muscle, the nerve endings release a neurotransmitter called acetylcholine. Acetylcholine binds to receptors on the muscle and activate a process that causes the muscle to contract.

In myasthenia gravis, antibodies (immune proteins produced by the body's immune system) block, alter, or destroy the receptors for acetylcholine at the neuromuscular junction, which prevents the muscle from contracting. This is most often caused by antibodies to the acetylcholine receptor itself, but antibodies to other proteins, such as MuSK (Muscle-Specific Kinase) protein, also can impair transmission at the neuromuscular junction.

The thymus gland controls immune function and may be associated with myasthenia gravis. The thymus gland grows gradually until a person reaches puberty and then gets smaller until it is replaced by fat. Throughout childhood, the thymus plays an important role in the development of the immune system because it is responsible for producing T-lymphocytes or T cells, a specific type of white blood cell that protects the body from viruses and infections.

In many adults with myasthenia gravis, the thymus gland remains large even after a person becomes an adult. People with the disease typically have clusters of immune cells in their thymus gland and may develop tumors in the thymus gland known as thymomas. Thymomas are most often harmless, but they can become cancerous. Scientists believe the thymus gland may give incorrect instructions to developing immune cells, ultimately causing the immune system to attack its own cells and tissues and produce acetylcholine receptor antibodies.

Several common medications, including statins, which are prescribed to help lower cholesterol, may rarely worsen myasthenia gravis. Individuals with myasthenia gravis should talk with their healthcare provider about how any medication might interact with the disorder.

Diagnosing myasthenia gravis

There are several tests that can confirm a diagnosis of myasthenia gravis:

Physical and neurological examination—A doctor will review your medical history and conduct a physical examination. In a neurological examination, the physician will check:

Muscle strength and tone

Coordination

Sense of touch

Eye movements



Electrodiagnostics—Diagnostic tests include:

Repetitive nerve stimulation repeatedly stimulates the nerves with small pulses of electricity and tests the electrical responses of the muscle receiving those stimuli.



Single fiber electromyography (EMG), which is considered the most sensitive test for myasthenia gravis, detects impaired nerve-to-muscle transmission. EMG can be very helpful in diagnosing mild cases of myasthenia gravis when other tests fail to demonstrate abnormalities.



Blood test—People living with myasthenia gravis may have abnormally elevated levels of acetylcholine receptor antibodies or anti-MuSK antibodies. A blood test also can detect these antibodies. In some individuals with myasthenia gravis, neither of these antibodies is present; this is called seronegative (negative antibody) myasthenia.

Because weakness is a common symptom of many other disorders, it can be difficult to diagnose myasthenia gravis in people who have mild weakness or whose weakness is restricted to only a few muscles. - Source: MayoClinic. Contact Corachia Ockhuizen at 081 747 6470 for more information on the MG Myasthenia Gravis Foundation Namibia

Did you know?

Life

Most people with myasthenia gravis live to an average life expectancy, with treatments available to help reduce and improve muscle weakness.

STATS

Symptoms

Weakness of the eye muscles (ocular myasthenia)

Drooping of one or both eyelids (ptosis)

Blurred or double vision (diplopia)

Changes in facial expressions

Difficulty swallowing

Shortness of breath

Impaired speech (dysarthria)

Weakness in the arms, hands, fingers, legs, and neck

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