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
Many people with myasthenia gravis feel strongest shortly after waking. That’s because sleep allows the neuromuscular junction time to recover, which can temporarily improve the ability of nerves to activate muscles.
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
By late afternoon or evening, repeated muscle use can lead to more noticeable weakness. Symptoms can include:
- 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.
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