Myasthenia gravis: Year of the Zebra 2024

Myasthenia gravis is an autoimmune disorder that causes weakness in skeletal muscles. It occurs when the body mistakenly produces antibodies that attack the neuromuscular junction, which is the meeting point between nerve endings and muscle fibers.

Typically, when the brain sends a signal to move a muscle, it travels down motor nerves until it reaches the neuromuscular junction. At this junction, nerve cells release a chemical messenger called acetylcholine, a neurotransmitter which crosses a small gap and binds to receptors on the surface of muscle cells, triggering muscle contraction.

With myasthenia gravis, antibodies bind to these receptors, blocking their interaction with acetylcholine and weakening muscle contraction. Over time, these antibodies can damage and reduce the amount of receptors on the muscle cell surface, further leading to weak and easily fatigued muscles.

Although it is unclear why, myasthenia gravis tends to affect young females in their twenties and thirties and older males in their sixties and seventies. It is also more common in people who have a thymoma, which is a type of tumor that develops in the thymus gland.

The hallmark symptom of myasthenia gravis is muscle weakness that worsens after activity and improves with rest. Initially, myasthenia gravis may only affect the muscles that control movement of the eye and eyelids, causing symptoms like double vision or drooping eyelids. When the arm and leg muscles are involved, people might experience severe fatigue and difficulties with walking or climbing stairs. Weakness in the muscles responsible for swallowing and speech production can cause symptoms like a change in voice and slurred speech, as well as difficulty swallowing.