Up to 20% of MS diagnoses may be wrong, like Christina Applegate's

A multiple sclerosis expert answers questions about MS misdiagnosis after Christina Applegate said she doesn’t have the chronic condition after all.

Actor Christina Applegate announced Tuesday that she had been misdiagnosed with multiple sclerosis after years of believing she had the condition — and experts say her experience is more common than many people realize.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 at the Cedars-Sinai Medical Center department of neurology, said that almost 1 in 5 people who are told they have multiple sclerosis "didn't actually have it." There is no single test to confirm MS, a disease where the body's immune system attacks the central nervous system. Symptoms vary from person to person and it can progress in different ways, according to the National Multiple Sclerosis Society.

How can an MS misdiagnosis be discovered?CBS News spoke with Dr. Robert Brumel, the director of the Mellon Center for MS at Cleveland Clinic, a multidisciplinary center that cares for more than 11,000 patients with multiple sclerosis, about the risk of an MS misdiagnosis and what patients need to know. He said a misdiagnosis is most often found when a person seeks out a second opinion because their symptoms aren't getting better. This doesn't always mean the diagnosis is wrong, but can be an indicator for more advanced tests. (Brumel said most MS