Christina Applegate's MS misdiagnosis after 5 years of treatment exposes alarming medical reality

Christina Applegates recent revelation that she was misdiagnosed with multiple sclerosis is raising questions about how the disease can be confused with other conditions — even after years of treatment.

The actress, 54, shared the news during an Oct. 20 episode of her podcast, "MeSsy," alongside co-host Jamie-Lynn Sigler, saying she was in a complete "state of shock."

Applegate was first diagnosed with MS in 2021 after experiencing debilitating symptoms and undergoing extensive testing, including brain and spinal MRIs and a . She said doctors found dozens of lesions on her brain.

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After years of treatment, her doctor decided to stop her regular infusions and monitor her B cells.

"And my B cells didn't change. They didn't go higher, they didn't go lower, they didn't change, and she had never seen that. So I guess that began kind of a study into my diagnosis," Applegate shared.

After additional brain scans, the doctor came into Applegates room and said, "Congratulations, you don't have MS."

The actress did not consider this to be good news, however.

"Because you don't get misdiagnosed and then all of a sudden [youre] better," she said. "I haven't gotten better … If anything, I've in some ways."

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Applegate noted that she has "every symptom" of someone with MS, adding that there are many conditions that mirror the disease.

She recalled that her MRIs clearly showed around 30 lesions, but said her neurologist identified a different feature — which she described as a "string" — that led to the conclusion that she did not have MS.

"So I'm back at square one [and] don't know what's going on with me."

Dr. Marwa Kaisey, an associate professor of neurology at Cedars-Sinai in Los Angeles, said during a follow-up "MeSsy" podcast episode that misdiagnosis of MS is "fairly common."

In a study of patients referred to MS clinics at UCLA and Cedars-Sinai, Kaisey — who has not treated Applegate — said she found that nearly one in five who arrived with an ultimately did not have the disease.

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"Some [had been diagnosed] for decades," she said. "And a majority of them were on medication to treat their MS."

The primary challenge, according to the doctor, is that there is no single test for MS. "It's not like we have something like a pregnancy test that says, yes, you have it, no, you don't."

Instead, Kaisey said, "It's a list of criteria, some of which remain a little bit subjective."

Most misdiagnosed patients did have some type of white matter spots, or lesions, on their , Kaisey noted, but they had a different cause that was not MS.

Newer imaging techniques may help doctors distinguish MS lesions from white matter spots caused by other conditions.

Kaisey pointed to the "central vein sign," an MRI finding that looks for small running through the center of lesions, which is a characteristic associated with MS. The sign was incorporated into updated MS diagnostic criteria to help doctors determine whether white matter lesions are consistent with the disease.