context: At first glance, it might not seem like multiple sclerosis ( MS) and strokes have a lot in common. When you have a stroke, a blocked or burst blood vessel cuts off the blood supply to part of your brain. With MS, you have a lifelong disease where your immune system, your body's defense against germs, attacks the nerves in your brain and spinal cord. Two very different conditions, but they can look and feel alike. That's because they both harm your brain. The symptoms of MS and strokes can be close enough that even doctors don't always get it right. It's important to know the difference. While you can wait to talk to your doctor about an MS flare-up, waiting to get treatment for a stroke can be a matter of life and death. The common ground for MS and strokes is the symptoms they cause. Depending on which part of the brain they affect, both can make you: Feel confused or have changes in the way you think and focus Get dizzy and lightheaded Get a headache Feel numb or weak in your arms, face, or legs Have speech problems, like slurring Find it hard to walk Have problems seeing It may not be easy. A test called an MRI may be able to show the difference pretty clearly, but that doesn't help when you're at home with a numb arm or blurred vision and wondering what to do. If you have any doubts, call 911 right away. None of these are foolproof, but here are some clues you can look for: Pay attention to how fast your symptoms came on. A stroke is sudden. One moment, you're fine. The next, you're definitely not. An MS flare-up tends to show up more slowly, usually over hours or days. So the speed at which the symptoms strike can give you some idea of what's going on. But if you're asleep when a flare-up starts or you miss the first signs, it may not be so clear. Keep track of how your MS flare-ups usually go. You know your body best. Over time, you'll likely learn the ups and downs of your MS symptoms and figure out when you're having a flare-up. You may be able to use that experience as a way to tell the difference between a flare-up and the symptoms of a stroke. That said, when you have a flare, your symptoms get much worse or you may get new ones. And that may throw off your judgment. So always keep your doctor in the loop. Watch for unusual symptoms. Loss of ability to speak and understand aren't very common symptoms of MS. So if you don't normally have this problem with a flare-up, they could be a stroke warning sign. MS can cause other issues that stroke normally wouldn't, like muscle spasms, pain, and bowel and bladder problems. Having these symptoms could mean it's more likely a flare-up. It's also unusual to develop MS after age 50, while strokes are more common after that age. Keep in mind that these are just clues, and you may need a doctor's help to sort it out. Always get medical help if you have any doubts about whether it's a stroke or MS. It takes experience to learn how to tell the conditions apart. Even then, it may not be clear. Given how serious a stroke can be, you're better safe than sorry. If it is a stroke, you don't have time to wait. Quick treatment can save your life and help prevent long-term problems. If it turns out to just be an MS relapse, that's important for your doctor to know, too. It could be a sign to make some changes in how you manage your MS. MS flares may need to be treated in the hospital with IV steroids. Pseudoflares caused by infection may also need treatment. One of the best things you can do is talk to your doctor about your chances of having a stroke. If you have problems like diabetes, heart disease, high blood pressure, or high cholesterol, your risk is higher. Your doctor can help you get those under control.