Learn The BasicsMyasthenia gravis (MG) is a rare disease characterized by weakness in the voluntary muscles. Depending on which muscle groups are affected, the symptoms may vary. Patients may also experience generalized fatigue affecting the entire body.
Eye muscles
The muscles in the eyelids and those responsible for moving the eyes are often the first affected in MG.
Eye muscle weakness leads to symptoms such as droopy eyelids that can affect one or both eyes and blurry or double vision, also called diplopia.
In some people with MG, eye muscle weakness is the only symptom ever experienced. This is known as ocular MG.
Face and throat muscles
Muscle weakness can also affect the face and throat in patients with MG.
This can lead to symptoms such as difficulty speaking and slurred speech. It can also cause difficulty chewing, which worsens as more time is spent chewing, and difficulty swallowing, which can lead to choking and inhaling food. Some patients may experience recurrent chest infections due to eating difficulties.
Weakness in the face muscles can cause changes in facial expression, like the inability to smile.
Neck, arm and leg muscles
Weakness in the neck muscles can lead to difficulties holding up the head, and weakness in the leg muscles may make walking challenging. However, leg muscle weakness is rarely serious enough for patients to require a wheelchair for mobility.
Arm weakness can make everyday tasks, like brushing teeth and washing hair, more difficult.
Muscle weakness affecting only the arms and legs is very uncommon in MG and is thought to affect only around 5% of patients.
Myasthenic crisis
In rare cases, muscle weakness can affect the diaphragm and other muscles used for breathing and cause shortness of breath.
Breathing muscle weakness can lead to a serious symptom called a myasthenic crisis. It’s characterized by worsening muscle weakness, which can lead to respiratory failure and be life-threatening if left untreated. Up to 90% of patients with myasthenic crisis require intubation and mechanical ventilation.
A ‘snowflake disease’
MG is sometimes called a “snowflake disease” because of the way each patient’s symptom set is unique, like each snowflake is unique.
In addition, like a snowflake, the symptoms may appear and disappear very quickly and can last from minutes to days.
Disease course
Not only do the symptoms of MG vary greatly from one person to another, but they also differ considerably according to the time of day and a patient’s age.
Muscle weakness tends to worsen towards the end of the day as the muscles are used and improves after rest.
Some days might also be worse than others, with symptoms fluctuating regularly. However, symptoms usually are at their worst within one to three years of disease onset.
Sometimes, the disease may go into remission, in which symptoms disappear altogether. The length of time during which no symptoms occur also varies from one person to another, but the remission periods last around five years on average. Some people may experience more than one remission period in their lifetime.
Reviewed by Debjyoti Talukdar, M.D., on June 6, 2025.