Actor Christina Applegate revealed Oct. 20 that she was misdiagnosed with multiple sclerosis. The revelation underscores how elusive an MS diagnosis can be and highlights the persistent challenge of diagnostic errors across the healthcare industry.
Seven notes:
1. Ms. Applegate, who was diagnosed in 2021, said on her podcast MeSsy that a test involving a spinal tap ruled out the disease. Her symptoms persist, however, leaving her “back at square one,” she said, according to CBS News.
2. Because no single test confirms MS, clinicians must piece together a wide spectrum of symptoms, imaging and biomarkers to make a diagnosis. Misdiagnosis usually occurs when abnormalities on patients’ brain scans are misinterpreted, Robert Bermel, MD, director of the Mellen Center for MS at Cleveland Clinic, told CBS News. While brain lesions are a common sign of MS, they can also be caused by migraines, smoking or high blood pressure.
3. Misdiagnoses are usually discovered after patients seek a second opinion because their symptoms aren’t improving, Dr. Bermel said. Persistent symptoms don’t always mean the diagnosis is wrong, but they can signal the need for more advanced testing.
4. Estimates of how often MS is misdiagnosed vary by study and patient population. About 17% of MS patients at Los Angeles-based Cedars-Sinai Medical Center and 19% at UCLA Health were misdiagnosed, according to a 2019 study of 241 patients. Migraine was the most common alternative diagnosis, followed by several neurological and spinal disorders.
“What that study showed, and a lot of subsequent studies showed, was that there were a lot of common disorders that were frequently mistaken for MS and shouldn’t have been,” study author Andrew Solomon, MD, a neurologist who co-authored the study, told NBC News. “A lot of these misdiagnoses could be prevented, but that requires a lot of education and implementation.”
5. Bruce Bebo, PhD, chief research & medical affairs officer at the National Multiple Sclerosis Society, told NBC News that the findings don’t necessarily represent all MS patients, as the study involved referred patients whose cases were already difficult or severe. Larger studies place the misdiagnosis rate between 15% and 20%, according to Dr. Bermel.
6. In 2025, an international committee of experts sponsored by the European Committee for Treatment and Research in Multiple Sclerosis and the National Multiple Sclerosis Society published revisions to the McDonald diagnostic criteria for MS in The Lancet Neurology. The update includes two new MRI markers that help distinguish MS lesions from those caused by other conditions, such as vascular disease or migraine.
7. MS misdiagnosis reflects a broader diagnostic safety problem across healthcare. Nearly 70% of diagnostic errors occur during the testing process, which includes ordering, processing and communicating results, according to a 2024 ECRI analysis of more than 3,000 patient safety events. In 2024, the CDC partnered with CMS and the Agency for Healthcare Research and Quality to develop new resources to help hospitals reduce diagnostic errors.
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