Myasthenia Gravis : An autoimmune neuromuscular disorder
Myasthenia gravis (MG) is an autoimmune neuromuscular disorder of the muscles and the nerves that control them.
Causes and incidence
Myasthenia gravis is classified under the category of autoimmune disorder that occurs when the body’s own immune system considers its own healthy tissues as foreign bodies and attacks them. In the individuals with myasthenia gravis, the body produces antibodies that block the muscle cells from receiving the messages (from neurotransmitters) from the nerve cells.
The exact cause of this disorder is unknown by in some cases it is linked with the tumors of the thymus gland (one of the major organs of the immune system).
Although MG can affect individuals of any age, but it is more commonly seen in young women and older men.
Myasthenia gravis causes weakness of the voluntary (skeletal) muscles. Voluntary muscles are those that are under your control. In other words, you think about moving your arm, and it moves. The muscle weakness of myasthenia gravis worsens with activity and improves with rest.
The muscle weakness can lead to a variety of symptoms, including:
- Breathing difficulty because of weakness of the chest wall muscles
- Chewing or swallowing difficulty, causing frequent gagging, choking, or drooling
- Difficulty climbing stairs, lifting objects, or rising from a seated position
- Difficulty talking
- Drooping head
- Facial paralysis or weakness of the facial muscles
- Hoarseness or changing voice
- Double vision
- Difficulty maintaining steady gaze
- Eyelid drooping
The health care provider performs a physical exam, including a detailed nervous system (neurological) examination. This may show:
- Muscle weakness – eye muscles are usually affected first
- Reflexes and feeling (sensation) are normal
MG can be a difficult diagnosis, as the symptoms can be subtle and hard to distinguish from both normal variants and other neurological disorders. A thorough physical examination can reveal easy fatigability, with the weakness improving after rest and worsening again on repeat of the exertion testing. Applying ice to weak muscle groups characteristically leads to improvement in strength of those muscles. Additional tests are often performed, as mentioned below. Furthermore, a good response to medication can also be considered a sign of autoimmune pathology.
Tests and investigations include:
- Acetylcholine receptor antibodies associated with this disease
- CT or MRI scan of the chest to look for a tumor
- Nerve conduction studies
Muscle fatigability can be tested for many muscles. A thorough investigation includes:
- looking upward and sideward for 30 seconds: ptosis and diplopia
- looking at the feet while lying on the back for 60 seconds
- keeping the arms stretched forward for 60 seconds
- ten deep knee bends
- walking 30 steps on both the toes and the heels
- five sit-ups, lying down and sitting up completely
- “Peek sign”: after complete initial apposition of the lid margins, they quickly (within 30 seconds) start to separate and the sclera starts to show.
There is no known cure for myasthenia gravis. However, treatment may allow you to have prolonged periods without any symptoms (remission).
Lifestyle changes often help you continue your daily activities. The following may be recommended:
- Scheduling rest periods.
- An eye patch is double vision is bothersome.
- Avoiding stress and heat exposure, which can make symptoms worse.
Medications that may be prescribed include:
- Neostigmine or pyridostigmine to improve the communication between the nerves and the muscles.
- Prednisone and other medications (such as azathioprine, cyclosporine, or mycophenolate mofetil) if to suppress the immune system response, if you have severe symptoms and other medicines have not worked well.
Several medications may make symptoms worse and should be avoided. Therefore, it is always important to check with your doctor about the safety of a medication before taking it.
Crisis situations, where muscle weakness involves the breathing muscles, may occur without warning with under- or overuse of medications. These attacks seldom last longer than a few weeks. Hospitalization and assistance with breathing may be required during these attacks. Often procedure called plasmapheresis is used to help end the crisis. In this technique, the clear part of the blood (plasma) containing the antibodies is removed from the body and replaced with donated, antibody-free plasma or with other fluids.
Plasmapheresis may also help reduce symptoms for 4 – 6 weeks and is often used before surgery. Intravenous immunoglobulin infusions may work as well as plasmapheresis. In this technique, a large amount of helpful antibodies are given directly into the bloodstream.
Surgery to remove the thymus (thymectomy) may result in permanent remission or less need for medicines, especially when there is a tumor present.
Patients with eye problems may try lens prisms to improve vision. Surgery may also be performed on the eye muscles.