Why Is Multiple Sclerosis So Commonly Misdiagnosed?

More than five years after revealing that she had multiple sclerosis ( MS ), Christina Applegate announced on Tuesday that she was misdiagnosed with the condition on the most recent episode of her and Jamie Lynn Sigler’s podcast, MeSsy. This was her first time back on the show, she said, after taking a seven-month break to “process” the news after receiving it from her doctor.

“She came into my room and said, ‘Congratulations, you don’t have MS,’” Applegate recalled on the podcast. “I was, like, not happy at all. Everybody else was so happy.” Now, she says she’s “back at square one,” working with doctors to try to identify the actual cause of her debilitating symptoms.

As it turns out, what happened to Applegate isn’t all that unusual. According to a 2019 study out of Cedars-Sinai, nearly 20 percent of patients once informed they were suffering from MS were actually given the wrong diagnosis.

But why is a condition estimated to affect nearly one million people in the United States misdiagnosed so frequently? And why are these misdiagnoses so problematic? Rolling Stone spoke with a neurologist specializing in MS to find out.

Multiple sclerosis is a chronic, progressive neurological disorder as well as an immune-mediated disease, meaning it causes an abnormal immune system response. (Autoimmune diseases, when the body attacks its own healthy tissue, are a subset of immune-mediated disease.) More specifically, in MS, the immune system damages myelin , the protective coating around the nerve fibers in the brain and spinal cord. Myelin’s job is to help nerves send messages quickly, so when it’s compromised , messages between your brain and body slow down or get blocked altogether, causing MS symptoms.

The symptoms of MS can vary from person to person, as well as during the course of the disease, depending on which nerve fibers are affected. Common symptoms include numbness or tingling of the face, torso, or limbs; extreme mental and/or physical fatigue; vision problems (like double vision or inflammation of the optic nerve); muscle weakness; and dizziness. In some cases, MS can cause mood and/or cognitive changes. Editor’s picks The 250 Greatest Albums of the 21st Century So Far The 100 Best TV Episodes of All Time The 500 Greatest Albums of All Time 100 Best Movies of the 21st Century

However, in some cases, people who go on to be diagnosed with MS don’t have any symptoms. “It’s called radiologic isolated syndrome,” says Tirisham Gyang, MD , a neurologist and associate professor of neurology at the Ohio State University Wexner Medical Center. “They get an MRI for a different reason, like headaches or an accident. Nobody is thinking they have MS. They’ve never had any symptoms of MS. Yet the brain MRI looks just like MS.”

Because of the evolving understanding of multiple sclerosis, the diagnostic criteria were revised in 2024 to be more sensitive and specific.

Prior to that, MS was exclusively a clinical diagnosis — meaning the patient had to have specific symptoms, like vision loss or weakness, for example.