American actor Christina Applegate says she was misdiagnosed with multiple sclerosis, after she first publicly announced her battle with the disease in 2021. How did it happen? According to latest data from the Public Health Agency of Canada, 290 in every 100,000 Canadians over the age of 20 live with the autoimmune disease of the central nervous system. Seven out of 10 are women. The symptoms of MS are unpredictable and vary because it affects the brain and spinal cord. Symptoms can include difficulty walking, lack of co-ordination, vision problems, fatigue, cognitive changes, bladder and bowel dysfunction and pain, tingling or numbness. Applegate revealed the misdiagnosis on the latest edition of her podcast “MeSsy,” which she hosts with fellow actor Jamie-Lynn Sigler, saying she doesn’t “know what’s going on” with her. So far, she has not been given a new diagnosis. The actor says the news of her misdiagnosis has put her in a tough spot because she has become a prominent advocate for people with MS, adding that she feels like she “let everybody down.” According to a medical expert who is not involved with Applegate’s care, other conditions have overlapping symptoms with MS, which could lead to a misdiagnosis. Dr. Michael Kornberg, associate professor or neurology at Johns Hopkins University, told CTV Your Morning on Thursday that there is no “one single test” that is positive in everyone with MS and negative for other conditions. “The challenges are that MS affects the brain, the spinal cord. These are organs that are not very accessible. We’re not doing biopsies on individuals,” Kornberg said. “(Diagnosis) is really a combination of having typical neurologic symptoms, typical findings on a brain MRI, supplemented by other tests like spinal fluid, and there’s other conditions that have overlapping symptoms.” Oftentimes, someone has neurological symptoms that are “somewhat unusual or atypical” for MS, along with abnormalities on a brain MRI that could look consistent with MS. “That will lead to the misdiagnosis,” he explained. Misdiagnosis isn’t a “common scenario,” Kornberg said, but it does happen. He said studies have shown that five to 20 per cent of people who are initially diagnosed with the disease will ultimately be told it was the wrong diagnosis. Speaking to The Associated Press about Applegate’s case, another doctor estimated the misdiagnosis rate at about 10 per cent. “It’s never wrong to seek a second opinion. I think it is always good practice to be seen by a neurologist who has a good bit of experience in multiple sclerosis,” Kornberg said, speaking about whether a patient should seek a second opinion if they’ve been diagnosed with MS. According to the medical expert, some neurological symptoms can vary day to day. MS symptoms don’t typically migrate like that, and last for more than 24 hours. “When you have symptoms that are kind of quick on, quick off, or if they’re associated with non-neurologic symptoms like joint pain, joint swelling, skin rashes… things that are harbingers of a more systemic autoimmune process,” those are times when a second opinion can be helpful, Kornberg said. He added that Applegate’s misdiagnosis was “troubling,” because it doesn’t bring her any closer to symptom relief or treatment as she lives with chronic symptoms. “Her team of doctors is going to be revisiting her symptoms and exploring other possibilities, and as she also articulated, it’s really tough for people who have lived with this for five years,” Kornberg said. “They felt like they knew what was going on in their body, and to have that taken away is really difficult.” With files from The Associated Press