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Myasthenia Gravis

Myasthenia gravis is a clinical condition where antibodies are generated within {the} body that attack {the} junctions between {the} nerves and {the} muscles, resulting in muscle weakness and tiredness. At {the} junction of {the} nerves and muscles (also called neuromuscular junction) are receptors called acetylcholine receptors. These receptors have {the} capability of binding to acetylcholine, a neurotransmitter that helps promote conduction of electrical impulses from {the} nerves to {the} muscle. Blocking of these in myasthenia gravis is what results in {the} clinical features.

In this article, we shall briefly discuss {the} signs and symptoms of myasthenia gravis, and touch upon {the} different management options available.

Clinical features

Patients with myasthenia gravis experience {the} typical feature of muscle fatigue. The muscles become weaker with time, and are particularly vulnerable when undergoing continuous activity. One of {the} muscle groups that are often involved is {the} eyelid. Patients have droopy eyelids - a condition called ptosis. This can affect one or both of {the} eyelids and can have additional effects such as double vision. This is called ocular myasthenia.

Other symptoms that may possibly be seen include slurred speech, difficulty walking, weakness of {the} muscles of {the} arms and legs, difficulty swallowing and even muscles that are required for breathing (in advanced cases).

Pathophysiology

The main underlying defect in myasthenia gravis (as described briefly above) is autoimmunity. This means that there are antibodies within {the} body that act against {the} individual’s own proteins. These antibodies are called auto-antibodies. There is some genetic link in myasthenia, though in most cases {the} underlying abnormality lies within a gland in {the} chest called {the} thymus gland. The auto-antibodies act against {the} acetylcholine receptor, thus interrupting normal neuromuscular unction function. This causes muscle weakness.

 

Diagnosis

Most cases of myasthenia gravis, particularly ocular myasthenia can be diagnosed by clinical history and physical examination. A simple bedside test can be performed where {the} patients are asked to look up at a point (or pencil) by only elevating their eyes and keeping their head still. In a few seconds, {the} muscles of {the} eyelid become weak and start to droop, resulting in ptosis. Blood tests may possibly be performed to identify {the} antibodies. Electromyography tests that assess conduction of nerve impulses in {the} muscles is also a useful tests.

In ocular myasthenia, {the} edrophonium test may possibly frequently be used. It is based on {the} principle that injection of edrophonium chloride will temporarily reverse ptosis in myasthenia patients, and not it other causes of ptosis.

Treatment

Medical treatment includes acetylcholinesterase enzyme blockers such as neostigmine and pyridostigmine. These drugs are useful in managing muscle weakness effectively, and are often started by {the} doctor in small doses. Stronger medications such as steroids, mycophenolate mofetil and azathioprine suppress {the} immune system and reduce {the} production of antibodies and are useful as well.

Special treatments include plasmapheresis - a procedure that helps remove these antibodies from {the} body. Intravenous immunoglobulin can also be used to eliminate these antibodies by binding to them. Finally, removal of {the} thymus gland may possibly also be offered - a procedure called thymectomy.

Surgery to raise {the} eyelid may possibly also be performed.

Conclusion

Myasthenia gravis is a condition that affects {the} muscles, particularly {the} eyes. Diagnosis is fairly straight forward, and treatment options are numerous.