Hollywood actor Christina Applegate has revealed she’s been devastated to learn she is fighting a mystery illness after being misdiagnosed with multiple sclerosis (MS).

Applegate, 54, was told she had the disease in 2021 while filming the third and final season of Netflix series Dead To Me after developing a number of severe symptoms.

WATCH THE VIDEO ABOVE: Christina Applegate reveals MS misdiagnosis

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Illness has forced Applegate to use a wheelchair and cane to attend public events such as her Hollywood Walk of Fame induction in 2022, and the Primetime Emmys in 2024, where she presented an award.

MS causes the immune system to attack nerve cells in the brain and spinal cord, disrupting the brain’s ability to send signals across the body.

It leads to muscle and motor issues, severe fatigue, cognitive and mood changes, vision issues, and bladder and bowel complications.

There is currently not a test for MS, meaning those with symptoms usually spend years seeing multiple doctors to get a diagnosis.

But in a shocking twist, Applegate appeared on the MeSsy podcast with co-host Jamie-Lynn Sigler on Monday to reveal she was misdiagnosed with MS despite having all the symptoms.

“I had every symptom of someone with MS. Every single one,” Applegate said.

The Married With Children star said her doctor had her taking a number of infusions “that plays havoc on your body” for years before taking her off them to see how her immune system reacted.

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Removing the infusions would cause levels of B cells to fluctuate in an MS patient, but for Applegate they remained stable.

“You’re not going to freaking believe this ... (The doctor) came into my room and she said: ‘Congratulations, you don’t have MS’,” Applegate said.

While it may appear as a cause for celebration, the actor said it’s a lot more complicated.

After her doctor broke the news, Applegate said “I was not happy at all” because she was left with more questions about the health issues that upended her life and led to her retirement from acting.

“You don’t get misdiagnosed, and all of a sudden ‘I’m better’. I haven’t gotten better, Jamie. If anything, I’ve gotten worse in some ways,” she said.

“I still have to use wheelchairs when I go to the doctor’s office. I can’t walk from the car to the room. I’m still in this.

“Nothing magical happened when she said, ‘You don’t have MS’. Nothing magical happened.

“So, I’m back at square one, that I don’t know what’s going on with me.”

Applegate revealed she is now undergoing a number of further tests to find out what is causing her symptoms, but revealed the emotional impact of becoming the “poster child” for MS only to find out she doesn’t have the disease.

“I feel like I let everybody down,” she said.

“I had a reason as to why my day sucked every day and now I don’t have a reason ... It’s very unnerving and it’s really confusing for me.”