Muscle weakness is the main symptom of myasthenia gravis. The eye and facial muscles and those that control swallowing are commonly affected.
The symptoms of myasthenia gravis can come on suddenly, but it may take some time before the condition is correctly diagnosed.
Weakness of the eye muscles is often the first symptom to develop, although in some cases slurred speech or swallowing problems can occur first. The severity of muscle weakness varies from one person to another.
The muscle weakness of myasthenia gravis is not usually painful in itself, but people with the condition often experience aching muscles, particularly during periods of physical activity.
Eyes, eyelids and face
In myasthenia gravis, one or both eyelids may droop (ptosis). You may also have blurred or double vision.
Most people with the condition have problems with their eye muscles at some point. In some cases, the eye muscles remain the only muscles affected. This is known as ocular myasthenia.
Where the facial muscles are involved, a person's facial expression may be affected. For example, in some cases, a person may appear to have a "snarling" smile because of lower facial weakness.
Swallowing and breathing
If the muscles around your mouth are affected, you may have difficulty swallowing (dysphagia), chewing and talking. This can lead to impaired speech and a nasal-sounding voice.
Some people with myasthenia gravis also have breathing difficulties, particularly when exercising or lying flat.
A person with moderate to severe swallowing or breathing problems will need to be admitted to hospital to receive urgent medical care (breathing assistance). This is known as a myasthenic crisis.
Limbs and movement
Myasthenia gravis can sometimes affect the muscles of the arms, legs and neck. This can cause mobility problems, such as a waddling gait, head drop and difficulty performing physical tasks such as lifting.
Physical activity often leads to tiredness because the muscles are weak.