Myasthenia gravis is a disease that affects the way that muscles receive signals from nerves. Myasthenia is Greek for “muscle weakness,” which is a good description of this disease’s symptoms. Muscle weakness, which worsens after physical activity but gets better with rest, is the primary symptom of the condition.
Weakness may occur in any skeletal muscle, but smaller muscles in the face are commonly affected. This leads to symptoms that may include:
- difficulty chewing or swallowing,
- speech impairment,
- altered facial expression,
- drooping eyelids, and
- blurred vision.
Weakness in the limbs is often a symptom when larger muscles are affected. One of the most serious consequences of myasthenia gravis is a myasthenic crisis, which occurs when the respiratory muscles that allow us to breathe are affected. Someone in myasthenic crisis may need a machine (ventilator) to help them breathe if they have trouble on their own.
An understanding of how nerves work with muscles is important to understanding the effects of myasthenia gravis. The brain sends signals through the nerves, telling them which direct body parts to move. The signals travel down nerves to nerve endings, which are located very close to—but not touching—muscle fibers. Nerves release chemicals called neurotransmitters to send signals that bridge the gap between the nerves and muscles. Neurotransmitters bind to molecules on the surface of the muscle cells (receptors) that send a signal inside the cell. Acetylcholine is a neurotransmitter that causes muscle movement when it binds to its receptor. The normal interaction between a neurotransmitter and receptor doesn’t always work as smoothly as it should. In some cases, the immune system interferes, producing proteins called antibodies that are meant to protect the body from substances that might harm it. In the case of myasthenia gravis, the immune system makes antibodies that bind to acetylcholine receptors, which prevents the interaction between the neurotransmitters and receptors.
The disease typically occurs in women under 40 and men over 60, but it can develop at any age. Myasthenia gravis may be debilitating, but the good news is that symptoms can usually be controlled with medication. Steroids can help limit the production of antibodies that target acetylcholine receptors. Drugs called acetylcholinesterase inhibitors increase muscle strength by slowing the breakdown of acetylcholine. When neurotransmitters remain for longer periods of time, signals to the muscles are more likely to go through.
As you enjoy the outdoors and weather during Myasthenia Gravis Awareness Month, keep in mind all the things your muscles and nerves are doing without you even thinking about it.
Rebekah Morrow, PhD, is an assistant professor of immunology and microbiology at the Alabama College of Osteopathic Medicine.