What is myasthenia gravis? Tennis legend Monica Seles diagnosed

Monica Seles, the nine-time Grand Slam champ who once dominated the court with her signature two-handed style, is facing a new kind of opponent — and this one isn’t standing on the other side of the net.

The 51-year-old International Tennis Hall of Famer recently revealed she’s been quietly battling myasthenia gravis, a rare neuromuscular disease, for the past three years.

“It took me quite some time to really absorb it, speak openly about it, because it’s a difficult one,” Seles told the Associated Press. “It affects my day-to-day life quite a lot.”

The tennis legend broke her silence just days before the 2025 US Open kicks off in Flushing Meadows, hoping to raise awareness about the chronic condition she’d never heard of until it landed in her own court.

Here’s everything you need to know.

What is myasthenia gravis?

It’s a rare autoimmune disorder that causes muscle weakness, often affecting those that control your eyes, face, neck, arms and legs, according to the Cleveland Clinic. 

The condition strikes when the body’s immune system turns on itself, producing antibodies that block or destroy the receptor sites your muscles need to receive signals from the brain in order to move.

With fewer working receptors, the message doesn’t get through — leading to a communication breakdown between brain and body. As a result, the muscles feel weak and tire out fast, even from everyday tasks.

What are the symptoms of myasthenia gravis?

For more than half of those with the condition, the first signs affect the eyes, often causing double vision or drooping eyelids, per the Mayo Clinic.

About 15% experience early symptoms that affect their face and throat muscles, which can:

• Make speech slurred or soft, sometimes sounding nasally, depending on which muscles are affected.
• Cause trouble chewing and swallowing, making it harder to eat, drink or take pills.
• Change facial expressions, like turning a smile into a snarl.

Myasthenia gravis can also weaken the neck, arms and legs, making it tough to lift things, walk steadily or even hold your head up.

Seles first noticed that something was wrong when symptoms started showing up on the court.

“I would be playing with some kids or family members, and I would miss a ball. I was like, ‘Yeah, I see two balls.’ These are obviously symptoms that you can’t ignore,” she told the AP. 

Then came the muscle weakness. “Just blowing my hair out … became very difficult,” the tennis champ said.

The weakness usually worsens the more you use the affected muscles but can improve with rest, which can sometimes make diagnosis difficult.

“Patients can present with fatigue and then healthcare providers have no idea what to do with that,” Dr. Beth Stein, director of neuromuscular diseases at St. Joseph’s Health in New Jersey, told The Athletic. 

Who’s at risk for myasthenia gravis?

It can strike anyone, but it’s most often diagnosed in women under 50 and men over 65, according to the Myasthenia Gravis Foundation of America.

It’s also slightly more common in people of African descent, though it affects all racial and ethnic backgrounds.

While still considered rare — affecting roughly 37 out of every 100,000 Americans — cases are on the rise. Experts believe this is at least partly because people are living longer lifespans and better tools have been developed to diagnose it.

What’s the outlook for someone with myasthenia gravis?

There’s no cure, but the condition can usually be managed with treatment, especially if it’s detected early, according to Johns Hopkins Medicine.

Treatment may include medications that suppress the immune system or intravenous immunoglobulin, a blood product that helps reduce the attack on the nervous system.

Doctors might also remove the thymus gland surgically, which can sometimes improve symptoms by altering the immune response.

Another option is plasmapheresis, a procedure that filters out abnormal antibodies from the blood and replaces them with healthy ones from donors.

For Seles, every day is about adapting.

“Some days are very extreme,” she told the AP. Other days, she plays tennis, pickleball and walks her dogs.

“As I tell kids that I mentor: ‘You’ve got to always adjust. That ball is bouncing, and you’ve just got to adjust,’” Seles said. “And that’s what I’m doing now.”

Is myasthenia gravis fatal?

Generally, no. Most people with myasthenia gravis have a normal life expectancy, but in rare cases, it can cause life-threatening complications.

That includes myasthenic crisis, a severe weakening of the muscles that control breathing, which can lead to respiratory failure and other medical emergencies

In such cases, a ventilator may be needed until muscle strength improves with treatment.