Tennis icon Monica Seles reveals myasthenia gravis diagnosis. What to know about the disease.

Tennis legend Monica Seles is opening up about her journey with myasthenia gravis, a neuromuscular autoimmune disease she was diagnosed with three years ago.

In a recent interview with The Associated Press, Seles, 51, said she chose to share her diagnosis ahead of the U.S. Open later this month to raise awareness about the disease, also known as MG.

Myasthenia gravis affects about 20 out of every 100,000 people in the world, according to the Cleveland Clinic.

"The actual number may be higher, as some people with mild cases may not know they have the condition," the clinic notes. "In the United States, there are approximately 60,000 people affected by myasthenia gravis at any given time."

Seles, whose career included nine Grand Slam titles and a place in the International Tennis Hall of Fame, said it took time to process the diagnosis.

"It took me quite some time to really absorb it, speak openly about it, because it's a difficult one. It affects my day-to-day life quite a lot," she told the AP.

Myasthenia gravis symptoms

Seles said she was referred to a neurologist after noticing symptoms such as double vision and weakness in her arms and legs.

"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," Seles said, adding even blowing out her hair "became very difficult."

In addition to eyes, arms and legs, myasthenia gravis can target muscles in the face and neck, according to the Cleveland Clinic, with symptoms that include:

Muscle weakness and fatigue

Droopy eyelids

Blurry or double vision

Limited facial expressions

Difficulty speaking, swallowing or chewing

Trouble walking

Muscles usually get weaker when someone is active and strengthen when they rest, the clinic adds.

What causes myasthenia gravis?

The autoimmune form of MG happens when the body's immune system mistakenly attacks itself, the Cleveland Clinic says. It is unclear why this happens.

"Studies suggest that certain immune system cells in your thymus gland have trouble identifying what's a threat to your body (like bacteria or viruses) versus healthy components," the clinic adds.

While the disease can affect people of any age, the Mayo Clinic notes it is more common in women younger than 40 and in men older than 60.

Myasthenia gravis treatment

There is no cure for myasthenia gravis, although treatment can help with symptoms.

Treatment options include medications, thymus gland removal surgery, lifestyle changes and more, according to the National Institute of Neurological Disorders and Stroke.

"Some cases of myasthenia gravis may go into remission, either temporarily or permanently and muscle weakness may disappear completely," the institute added.

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