For those with Lewy body dementia (LBD)—the second most common type of dementia after Alzheimer’s disease—symptoms can be even more stark. Patients may experience failing motor skills, cognitive impairment, behavioral changes, hallucinations, malfunctions of the nervous system, and more. Unfortunately, there is no single test to determine whether an individual has LBD—doctors must instead rely on a patchwork of clues and symptoms to form their diagnosis and create a treatment plan. That’s why experts are sounding the alarm about one symptom of this often-overlooked disease that occurs during sleep. Read on to discover the symptom that 80 percent of men with LBD report having. RELATED: If You Notice This While Walking, Your Dementia Risk Is Higher, Study Says. From memory to movement, neurodegenerative disorders can take a toll on many areas of your life. For those with Lewy body dementia, symptoms can even occur in sleep. According to a report from the Mayo Clinic, “the strongest predictor of whether a man is developing dementia with Lewy bodies—the second most common form of dementia in the elderly—is whether he acts out his dreams while sleeping.” They add that patients are “five times more likely to have dementia with Lewy bodies if they experience a condition known as rapid eye movement (REM) sleep behavior disorder than if they have one of the risk factors now used to make a diagnosis, such as fluctuating cognition or hallucinations.” RELATED: If You Eat This Once a Day, Your Dementia Risk Increases, Study Says. During the rapid eye movement (REM) stage of sleep, your arms and legs typically undergo a temporary paralysis which stops you from enacting your dreams in real life. However, the Mayo Clinic says that in some individuals with LBD, no such paralysis occurs and they are free to act out their dreams while asleep. These movements may include “kicking, punching, arm flailing or jumping from bed, in response to action-filled or violent dreams, such as being chased or defending yourself from an attack,” their experts say. Those who experience the sleep disorder are likely to laugh, talk or shout, and are prone to “emotional outcries” while sleeping. For more health news sent directly to your inbox, sign up for our daily newsletter. There can be other underlying causes for REM sleep disorder—Parkinson’s disease and multiple system atrophy, to name a few—but experts say the symptom is significantly prevalent among those with Lewy body dementia. “As many as 75 to 80 percent of men with dementia with Lewy bodies in our Mayo database did experience REM sleep behavior disorder. So it is a very powerful marker for the disease,” says Melissa Murray, PhD, a neuroscientist at Mayo Clinic in Florida. Presence of the disorder may also help medical professionals to distinguish between LBD and conditions with similar symptoms, including Alzheimer’s disease. “It can sometimes be very difficult to tell the difference between these two dementias, especially in the early stages, but we have found that only two to three percent of patients with Alzheimer’s disease have a history of this sleep disorder,” says Murray.ae0fcc31ae342fd3a1346ebb1f342fcb Given their similarities, it can be difficult to distinguish between Alzheimer’s, Parkinson’s disease, and LBD, but experts say that doing so successfully can make all the difference in a patient’s treatment plan. “When there is greater certainty in the diagnosis, we can treat patients accordingly,” Murray says. She adds that those with LBD who lack certain markers of Alzheimer’s “are more likely to respond to therapy—certain classes of drugs—than those who have some Alzheimer’s pathology.” Though there is currently no cure for Alzheimer’s, Parkinson’s, or Lewy body dementia, reaching a diagnosis early can have a significant and meaningful impact on a patient’s quality of life. RELATED: If You Notice This When Cooking, It May Be an Early Dementia Sign, Doctors Say.