A suspected misdiagnosis involving Christina Applegate has reopened a difficult question in neurology: what happens when a life-altering diagnosis is wrong—or when the right diagnosis arrives years too late?

DeMonica Amerson spent nearly two decades being treated for multiple sclerosis before specialists determined that she had neuromyelitis optica spectrum disorder (NMOSD), a rare autoimmune disease that can mimic MS. Her initial diagnosis followed years of uncertainty, including suspected optic neuritis and lupus. She eventually received daily injections, then monthly infusions, and built her life around managing MS. “I was mad, I was hurt, I was nervous, confused, all the things,” she recalled.¹

Her case illustrates one side of the problem: an incorrect diagnosis can expose patients to years of unnecessary treatment while delaying care for the disease they actually have. Doctors told CBS News that studies estimate 15% to 20% of people diagnosed with MS are later found not to have it. Because MS has no single definitive test, clinicians combine symptoms, MRI findings, spinal-fluid results and other markers. “There’s a lot of things going into the diagnosis,” said Dr. Josef Gutman.¹

But the opposite failure is also consequential. An account from a person living with MS describes years of psychiatric misdiagnosis before an MRI finally revealed neurological disease. The writer argues that patients can be dismissed whether their symptoms are attributed to mental illness, MS or something else—and that Applegate’s experience shows how unstable the boundary between “diagnosed” and “undiagnosed” can be.²

The perspectives converge on a central point: diagnostic uncertainty is not the same as imagined illness. Amerson ultimately shifted treatment and now says Uplizna is working well, while continuing to experience fatigue and pain. “I choose to keep going forward,” she said.¹ Yet her recovery from a wrong diagnosis does not erase the years lost. Nor does a correct diagnosis eliminate the fear that doctors may later reconsider it. The challenge is not simply to diagnose MS more accurately, but to ensure patients are taken seriously throughout the search for answers.