Myasthenia Gravis Fatigue: What Causes It and Why It Changes Throughout the Day

Myasthenia gravis (MG) is a chronic autoimmune neuromuscular condition that causes muscle weakness and severe fatigue. The fatigue associated with MG is often described as “fatigable weakness,” meaning the more you use a muscle, the weaker it becomes.

Because of this, symptoms often fluctuate — not just from day-to-day, but over the course of a single day. Someone with myasthenia gravis may wake up feeling relatively strong but find it harder to keep their eyes open, chew food, speak clearly, or lift their arms later in the day.

Why does this happen? And what can people with MG do to manage fatigue as symptoms change throughout the day?

To understand why fatigue happens in myasthenia gravis, it helps to look at the neuromuscular junction — the point where nerves communicate with muscles to tell them to move.

Because fewer receptors are available to receive the signal, communication between the nerve and muscle becomes less effective, says Xinli Du, PhD, a neurologist with the VCU Health Department of Neurology in Henrico, Virginia.

“Myasthenia gravis is the result of impaired nerve-muscle communication at the neuromuscular junction,” she says.

“It’s becoming clear that there are two parts to fatigue: One is directly related to the disease itself — the neuromuscular transmission. The second part is what we call central fatigue, which is also seen in other autoimmune disorders like multiple sclerosis.”

One hallmark of myasthenia gravis is that symptoms often fluctuate throughout the day, which happens because the nerve-muscle signal becomes weaker with repeated use.

As a result, muscles may work normally at first but gradually become weaker the more they are used. “That’s why people with myasthenia gravis often notice that their symptoms improve after rest,” Dr. Du says.

“Depending on the level of physical activity throughout the day, the degree of weakness can vary significantly,” she says.

Morning Strength

Usage Drain

Dr. Roda uses an analogy to help patients understand why the muscles feel weaker throughout the day with repeated activity.

“Imagine there’s a barrier, like a fence, that lies between the connection of the motor neuron and the muscle, and it must be scaled every time the muscle is used. For a healthy person, that fence is very small and poses no problems, but for a patient with myasthenia gravis, every time they do an activity, that fence gets higher and higher, and their ability to jump over it is lower,” says Roda.

Because the barrier to activating muscles is higher, repeated activity can quickly lead to weakness and fatigue, he says.

As muscles are used repeatedly, the limited number of working receptors becomes overwhelmed. Even small movements like blinking, chewing, speaking, or holding up the head can gradually drain the system.

Evening Decline

• Drooping eyelids
• Double vision
• Soft, nasal, or slurred speech
• Difficulty chewing or swallowing

Environmental Factors

Certain environmental conditions can also worsen fatigue.

“Hot and humid weather aggravates symptoms of myasthenia gravis because it accelerates the breakdown of the neurotransmitter used for communication between nerve and muscle,” Du says.

Stress, illness, and poor sleep can also contribute to worsening fatigue, says Roda.

Although myasthenia gravis fatigue cannot always be avoided, certain strategies may help reduce symptom flare-ups.

Strategic Pacing

“Because of the nature of the disease, patients have a limited amount of energy to use throughout the day. They need to plan ahead and use strategies to maximize their energy and minimize fatigue,” says Roda.

Planning activities around times when energy is highest can make a big difference.

Many people with myasthenia gravis find it helpful to schedule demanding tasks earlier in the day.

Du also recommends resting before activities that require significant muscle use.

“Until the disease is well controlled, it’s important to understand your body’s limitations and avoid overusing muscles,” she says.

Lifestyle Adjustments

Environmental changes can also help reduce fatigue. For example, maintaining a cooler environment can help prevent heat-related worsening of symptoms, Du says.

Breaking large tasks into smaller segments and taking regular breaks can also help conserve energy, says Roda.

Find ways to make repetitive tasks easier. For example, using electric tools such as an electric toothbrush or a can opener will keep those tasks from draining you.

Eye Care

Eye symptoms are often among the earliest signs of myasthenia gravis. Weakness in the muscles controlling eye movement can lead to drooping eyelids (called “ptosis”) or double vision.

Rest can temporarily improve muscle strength in myasthenia gravis. “When ptosis worsens, closing the eye or using an eye patch can temporarily improve eyelid muscle strength,” Du says.

For people who can still safely drive, resting your eyes before driving may help, says Roda.

Mealtime Pacing

“Chewing and swallowing are repetitive activities that can potentially cause muscle fatigue,” says Du.

• Eat when you feel strongest.
• Take smaller bites.
• Eat smaller, more frequent, meals.
• Eat more slowly.
• Choose softer foods later in the day.

Medication Timing

Many people with myasthenia gravis take pyridostigmine (Mestinon), a medication that improves nerve-muscle communication.

Pyridostigmine typically starts working within about 30 minutes and lasts roughly four hours, Du says. “It’s a good idea to plan more strenuous activities — including meals — during this window,” she says.

It’s important to get myasthenia gravis properly treated so that the disease is in remission or symptoms are very mild to improve fatigable muscle weakness, says Du.

She recommends discussing all aspects of your myasthenia gravis with your doctor, including:

• The type of myasthenia gravis you have and symptoms related to your MG
• What triggers or factors are most likely to worsen your MG symptoms and the best strategies to minimize them
• The basics of how your MG medications work and how to observe benefits and side effects

“It’s a team effort; your feedback to your doctor is equally important as the information your doctor provides to you,” says Du.

If your myasthenia gravis is well-controlled and you are still experiencing fatigue, talk with your doctor about checking your thyroid function and vitamin levels, she says. Sleep issues and depression should also be evaluated as potential contributing factors, says Du.

Roda agrees that identifying and treating sleep or mood issues can make a big difference in fatigue. “People with MG are statistically more likely to have a higher rate of nocturnal hypoxia, which can contribute to fatigue,” he says.

Unfortunately, you can have your motor symptoms well-controlled and still have fatigue, says Roda.

“All the fatigue in MG isn’t caused by motor symptoms. There are two parts to MG fatigue, and people can still have ‘central’ fatigue, which is different from fatigable weakness. It’s more similar to the type of fatigue that people with multiple sclerosis experience,” he says.

“We still have a lot to learn about this disease,” adds Roda.

• Myasthenia gravis causes a type of fatigue where muscles become weaker the more they are used, so many people feel stronger in the morning and more fatigued later in the day.
• The fatigue happens because the immune system disrupts communication between nerves and muscles.
• Rest can help temporarily by giving muscles time to recover. Planning activities for times when you feel strongest, taking breaks, avoiding heat, and timing tasks around medication may help manage fatigue.
• Getting myasthenia gravis well controlled is the most important step to improve muscle weakness, but if fatigue continues, talk with your doctor about other possible causes, such as sleep problems, mood issues, underactive or overactive thyroid, and low vitamin levels.