Christina Applegate speaking at the 2014 San Diego Comic Con International, for "The Book of Life", at the San Diego Convention Center in San Diego, California on July 25, 2014

Christina Applegate thought she had been living with multiple sclerosis since 2021. Now, after a fresh review using newer medical technology, doctors have told her that diagnosis was wrong—leaving her with the same debilitating symptoms but no clear explanation. She described the news as being back at square one on her podcast MeSsy, which she co-hosts with fellow actor and MS patient Jamie-Lynn Sigler.

Applegate said her doctors began taking a closer look after pausing her infusion treatment and observing that her B-cell levels did not change as expected. A later evaluation involving advanced brain-imaging technology led specialists to conclude that she does not have MS. The actor still reports weakness, pain and severe difficulty walking, however, and said her medical team must now investigate what has been causing those symptoms since 2021.

The uncertainty reflects a fundamental problem with MS: there is no single blood test, scan or examination that proves a person has it. Neurologists instead compare symptoms with evidence from MRI scans, spinal-fluid testing and examinations of the brain, spinal cord and optic nerves, while ruling out other conditions that can produce similar problems. That makes MS a diagnosis built from a pattern rather than a definitive yes-or-no test.

Diagnostic standards are evolving. The international 2024 revisions to the McDonald criteria, published in 2025, recognize the optic nerve as an additional location that can support an MS diagnosis. They also allow certain spinal-fluid findings to substitute for evidence that the disease appeared at different times, while newer MRI markers—including the central vein sign and paramagnetic rim lesions—can add specificity when available.

Those advances are intended to help doctors identify MS sooner without turning every suspicious scan into a diagnosis. The condition involves immune-system attacks on the central nervous system that damage myelin and nerve tissue, producing symptoms such as visual changes, numbness, dizziness, weakness and bladder problems. Early treatment matters because modern therapies can reduce new immune attacks and lower the risk of long-term disability, but treating someone for MS when they do not have it can expose that person to unnecessary risks while delaying the search for the real cause.

That is why a second opinion or later diagnostic review is not a sign that earlier care was pointless. New scans, revised criteria and a patient’s changing clinical history can all alter the balance of evidence. Applegate’s case is now moving into that uncomfortable middle ground: the MS label has been removed, but the symptoms remain, and finding an accurate diagnosis is the next medical challenge.

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Christina Applegate speaking at the 2014 San Diego Comic Con International, for "The Book of Life", at the San Diego Convention Center in San Diego, California on July 25, 2014 via Wikipedia Commons by Gage Skidmore with usage type - Creative Commons License. By Gage Skidmore - https://www.flickr.com/photos/gageskidmore/14781869542/, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=34342682