Christina Applegate discovers she never had MS after five years, but doctors still don't know what's wrong

Hollywood actress Christina Applegate has revealed that she was wrongly diagnosed with multiple sclerosis (MS) five years ago, leaving her without an explanation for the illness that has severely affected her life.

The 54-year-old actress broke down in tears while sharing the news on Tuesday's episode of her MeSsy podcast, which she co-hosts with fellow actress Jamie-Lynn Sigler.

Applegate recalled her doctor entering her hospital room and telling her that she did not have MS, a disease she had believed she was battling since 2021.

But the news did not bring the relief everyone expected.

"I was, like, not happy at all. Everybody else was so happy," she said.

The Dead to Me star explained that her condition had not improved despite the revised diagnosis. She still struggles to walk and sometimes requires a wheelchair.

So how did doctors discover the mistake after five years?

According to Applegate, questions emerged when her doctor stopped an infusion treatment and monitored her B cells, a type of immune cell.

The results prompted further investigation into her original diagnosis.

Neurologist Dr Marwa Kaisey explained on the podcast that MS can be difficult to diagnose because there is no single test that definitively confirms the disease.

She said nearly one in five people previously diagnosed with MS may actually have another condition.

Applegate also admitted feeling confused about her role as an advocate for people living with the disease.

The actress had stepped away from much of her acting career after experiencing debilitating symptoms.

Doctors are now investigating what has caused those symptoms since 2021.

For Applegate, the corrected diagnosis has not answered the question that matters most: what is making her sick? The answer to this question remains pending.