Up to 20% of MS diagnoses are incorrect, like Christina Applegate’s. Here’s what doctors say patients should know.

Actress Christina Applegate announced Tuesday that she had been misdiagnosed with multiple sclerosis after years of believing she suffered from the condition — and experts say her experience is more common than many people think.

Applegate shared the news on her podcast, MeSsy, where she and actor Jamie-Lynn Sigler discuss life with MS. In a follow-up episode, Dr. Marwa Kaisey, an associate professor in the department of neurology at Cedars-Sinai Medical Center, said that nearly one in five people who are told they have multiple sclerosis “don’t actually have it.”

There is no single test to confirm MS, a disease in which the body’s immune system attacks the central nervous system. Symptoms vary from person to person and can progress in different ways, according to the National Multiple Sclerosis Society.

How to discover a misdiagnosis of MS?

CBS News spoke with Dr. Robert Brumel, director of the Mellon Center for MS at the Cleveland Clinic, a multidisciplinary center that cares for more than 11,000 multiple sclerosis patients, about the risk of misdiagnosing MS and what patients need to know.

He said a misdiagnosis most often occurs when a person seeks a second opinion because their symptoms are not improving. This does not always mean the diagnosis is wrong, but can be an indicator for more advanced testing. (Brumel said that most MS treatments, especially those most commonly used, are “very safe” and would not put a person’s health at risk.)

When misdiagnosis occurs, the root cause is usually that abnormalities seen in brain scans were misinterpreted, Brumel said. Brain damage is considered a hallmark of MS, but it can also be caused by other medical problems such as high blood pressure, smoking or migraines. More advanced MRI sequences can help differentiate MS lesions from those caused by other conditions, Brumel said.

When concerns about a potential misdiagnosis arise, the next steps usually involve running specialized tests. These may include advanced MRI sequences to study lesions more closely, an MRI of the spine or spinal fluid analysis to identify specific abnormal immune proteins, Brumel said.

How common are MS misdiagnoses?

On MeSsy, Kaisey described MS misdiagnoses as “pretty common.” Brumel said the largest studies looking at the risk of misdiagnosis have shown that between 15% and 20% of patients diagnosed with MS do not actually have the disease.

Dr. Josef Gutman, director of the Long Island Comprehensive MS Care Center at NYU Langone, told CBS News that the broad spectrum of symptoms that can be attributed to multiple sclerosis makes the disease difficult to diagnose.

“It’s important to keep in mind that these symptoms are not necessarily specific in many ways. It’s sort of the history, combined with the MRI imaging, combined with other markers like cerebrospinal fluid, that help us make the diagnosis of MS,” Gutman said. “It’s not like diabetes, where there’s a blood test and if the result is above that number it’s diabetes, if it’s below that number it’s not. There are a lot of things to consider in the diagnosis.”

New diagnostic criteria for multiple sclerosis, developed by an international panel of experts in the field, were published in 2025 to try to reduce this risk. These criteria are more precise than before, according to Brumel, particularly when it comes to interpreting brain lesions.

“We place great importance on getting a correct diagnosis from the start, so that we can then confidently move on to highly effective MS treatment,” Brumel said.

What happens after a misdiagnosis of MS?

If a patient is misdiagnosed with multiple sclerosis, doctors will then begin looking for other potential causes of their symptoms, Brumel said.

They may suffer from an autoimmune disease, which can cause system-wide joint pain, swelling, and inflammation. Fibromyalgia is a “commonly identified diagnosis that mimics MS,” Brumel said. Migraines are also a possible diagnosis, as migraine can cause damage and other neurological symptoms. Chronic pain or fatigue syndromes can also “masquerade as MS,” Brumel said.

Sometimes a person may not have one disorder but several, Brumel said, noting that an incorrect diagnosis “really throws things off course.”

“MS can sometimes be a rewarding solution for a patient with many symptoms, because it’s seen as sort of a single, solitary cause,” he said, adding that he’s seen patients whose fatigue was caused by a sleep or thyroid disorder, while rheumatoid disease or fibromyalgia caused pain and swelling.

On her podcast, Applegate said that learning she had a misdiagnosis has made things more difficult at the moment, because there is still no explanation for the debilitating symptoms that are affecting her daily life and mobility.

“There’s no misdiagnosis and all of a sudden I’m better,” Applegate said. “If anything, my condition has gotten worse. So I’m back to square one where I don’t know what’s happening to me. And this is going to be an online investigation that my doctors are going to embark on just to find out what’s been happening since 2021, why did this happen?”

When to seek a second opinion

Even though only a minority of patients are misdiagnosed, anyone concerned about their diagnosis should always feel comfortable seeking a second opinion, Brumel said. Even when the initial diagnosis is correct, a second opinion can help the patient find other resources, he emphasized.

“MS is a life-changing diagnosis, and anytime someone is faced with something like this, I always think a second opinion is potentially necessary,” Brumel said.

Patients can also consult a multiple sclerosis expert, Brumel said. The National Multiple Sclerosis Society maintains an online registry and map of MS care centers and specialists nationwide. Brumel called the list “a very good starting point for identifying” nearby resources.

MS specialists are likely to be familiar with the diagnostic criteria, Gutman said. They are also more likely to experience conditions that mimic multiple sclerosis and have access to more specific tests that can help confirm a diagnosis.