Myasthenia Gravis
Myasthenia Gravis (MG) is an autoimmune disease where the body’s immune system uses antibodies to attack and damage receptors on your muscles. This results in muscle weakness. If this involves the muscles of the eyelid, it can result in lid droop (ptosis). If it involves the muscles of eye movement, it can result in double vision. The double vision and lid droop may vary, being worse when you are tired or later in the day.
Anatomy:
When you want to move a particular muscle, the brain sends a signal via the nerves that go to the muscle. When this signal reaches the end of the nerve, it causes release of a chemical (called a neuro-transmitter) that diffuses across a narrow gap (the synapse) between the nerve and muscle. On the muscle side of the synapse, there are chemical receptors that are waiting to detect this neuro-transmitter. When the neuro–transmitter connects with them, they begin the process that results in the muscle contracting.
In a patient with MG, when the neuro-transmitter is released and diffuses across the synapse, it does not produce normal muscular muscle contraction. This is because the normal receptors have been blocked or eliminated by antibodies produced by the body’s immune system. Repeat attempts at moving the muscle will result in a gradual increase in weakness.
Muscles that are used most frequently are most likely to be weak. This is particularly true of the muscles that move the eye, resulting in ocular misalignment (double vision) and the muscles that lift up the lid, resulting in eyelid droop (ptosis). Muscles anywhere within the body may be affected.
Ocular Myathenia Gravis with droopy eyelids.**
Ocular Myasthenia Gravis with eye muscle weakness resulting in crossed eyes and double vision.**
Physiology:
As with other autoimmune diseases, the reason for development of MG remains unclear. It is possible that some external challenge (viruses, etc.) may have caused the immune system to start acting in this fashion. At this time, however, we do not have full understanding of why certain patients develop MG.
Patients with MG may have other autoimmune problems (such as thyroid eye disease). Like other autoimmune diseases, MG often spontaneously improves, but symptoms may recur. Over time, there may be some lessening effect, but MG produces variable disease that may last for years or indefinitely.
Symptoms:
The most common symptoms of MG relate to weakness of the muscles that lift up the lid (ptosis) or move the eyes (double vision). When only the eye muscles are affceted, teh condition is called Ocular Myasthenia Gravis, or OMG.
However, MG can affect muscles anywhere in the body including those of swallowing or breathing. If problems with breathing or swallowing ever develop, it needs to be brought to the attention of Dr. Banik immediately.
It has been felt that when MG fails to cause general muscle weakness over 2 years or more that the chances of developing weakness in other non-ocular muscles in the future is low. This is probably true but not a guarantee that systemic weakness will not occur.
It remains a very important fact that MG does not produce pain or numbness. If pain is present, there is something else going on and this needs to be further investigated.
Signs:
The most common sign seen by Dr. Banik are droopy eyelids and eyes that don’t work together leading to double vision. The eye movement problems may be difficult to detect and often patients with double vision related to MG have had it years before a diagnosis is made. It is not unusual for previous evaluations or testing to have been normal.
Diagnosis:
The diagnosis of MG can be most easily made with a blood test, but 50-70% of patients with MG restricted to the eye muscles may not have a positive test. Thus, the finding of a negative blood test does not exclude MG.
Rest and ice tests may be helpful in the diagnosis of MG. Occasionally, Dr. Banik may perform additional testing with an injection of medication into your muscle to see if your symptoms improve. Finally, an EMG (electromyogram), has a relatively high sensitivity for the diagnosis of myasthenia. This test requires sophisticated equipment and is done by a neuro-muscular specialist.
Prognosis:
As with other auto-immune conditions, MG tends to come and go. Symptoms may suddenly become worse. They may be worsened by the use of certain antibiotics (such as the fluoroquinolone class) and other drugs. Once the diagnosis of MG is made, it is important that patients inform all their physicians, particularly if they are ever seen in an Emergency Department or are scheduled for any type of surgery with anesthesia.*
Treatment:
Unfortunately at this time, there is no known cure for the autoimmune condition MG. However, MG can be treated by medications that decrease the turnover of normal neuro-muscular transmitters. These may be taken in pill form and can be effective in improving weak muscles. Steroid therapy (prednisone) may also be effective in improving muscle function. As steroids need to be used for long term, it is important to consider whether or not the benefits are outweighed by the risks of side effects associated with steroids. Occasionally other medications that suppress immune function may help decrease the need for prednisone. If medications are not effective for eyelids or double vision, then lid or eye muscle surgery may be a long-term option.
Occasionally surgery to remove the thymus gland may be effective in treatment of MG and it is common to check for thymus enlargement with a chest CT scan.
During your visit, Dr. Banik will spend the time to review all the options for MG treatment which are best for you.
If you have any questions about droopy eyelids, double vision, or Myasthenia Gravis, schedule a complimentary phone consult with Dr. Banik. Just click the button below. You will be glad you did!
*Adapted from nanosweb.org
**Images courtesy of aao.org