Christina Applegate spent five years believing she had multiple sclerosis — undergoing infusion treatments, abandoning her acting career, becoming the public face of the disease — only to learn this week her doctors got the diagnosis wrong. If it can happen to a wealthy, connected celebrity, imagine what happens to ordinary Americans navigating the same system without the money or the platform.

Applegate revealed the news Tuesday on her podcast "MeSsy," tearfully explaining that her doctor discovered the error after taking her off an infusion treatment to observe her B-cell response. The cells didn't react as expected, triggering a re-examination of her diagnosis. "She came into my room and she said, 'Congratulations, you don't have MS,'" Applegate recounted. "I was, like, not happy at all."

She shouldn't be happy. Applegate said she still can't walk from the car to the doctor's office without a wheelchair. She still has numbness, tingling, and balance problems. She still does physical therapy three times a week. The only thing that changed is the label — and the years of treatment directed at the wrong disease. "You don't get misdiagnosed and then all of the sudden I'm better," Applegate said. "If anything, I've gotten worse."

Here is the number that should stop every American cold: Dr. Marwa Kaisey, an associate professor in Cedars-Sinai Medical Center's neurology department, said on the podcast that almost one in five people told they have MS "didn't actually have it." Misdiagnoses with the condition are "fairly common," Kaisey said, because there is no single definitive test for the disease. CBS News reported Kaisey's statistic straight; Variety didn't mention the doctor or her one-in-five figure at all, choosing instead to focus on Applegate's emotional state.

Applegate underwent spinal taps and MRIs when she was first diagnosed in 2021. Scans showed lesions on her brain. The medical establishment ran its standard battery and still got it wrong — for five years. She retired from acting after the finale of Netflix's "Dead to Me," where she used a wheelchair on set and the script was rewritten around her declining mobility. She launched a podcast and became what she called a "poster child" for MS advocacy. Now she says she feels like she "let everybody down."

"I lost everything. I lost my job … It stopped my life," Applegate said. "Nothing magical happened when she said, 'You don't have MS.'"

Variety noted that "new technology" led to the discovery of the misdiagnosis — raising the obvious question of why that technology wasn't deployed before five years of wrongheaded treatment. Neither outlet pressed that angle.

Applegate said a new medical investigation into her actual condition begins next week. She's back at square one, as she put it, after half a decade of fighting the wrong disease.

The medical establishment has no single test for MS and gets the diagnosis wrong nearly 20 percent of the time. The question isn't just what's wrong with Christina Applegate — it's what's wrong with a system that can mislabel one in five patients and call it routine.