In fact, experts say that while there is no one thing that can singlehandedly lead to diagnosis, there is a symptom that roughly one-third of MS patients report experiencing. If you notice this feeling when you nod your head, you should speak with your doctor about screening for other signs of MS. Read on to find out which symptom is a major red flag for multiple sclerosis, and why this strange phenomenon occurs. RELATED: If You Notice This On Your Skin, Get Checked for MS. Though each MS patient will experience the disease differently from the next, there are a few symptoms that are considered somewhat common across the board. Lhermitte’s sign, a symptom first noted in 1918 as a possible sign of MS, is one such symptom. A 2015 study published in the medical journal Annals of Indian Academy of Neurology found it was reported by over 33 percent of MS patients.ae0fcc31ae342fd3a1346ebb1f342fcb “Lhermitte’s sign (pronounced Ler-meets) is a sudden sensation resembling an electric shock that passes down the back of your neck and into your spine and may then radiate out into your arms and legs,” says the Multiple Sclerosis Trust, a U.K. health charity. “It is usually triggered by bending your head forward towards your chest” or nodding, they explain. RELATED: If You Notice This While Walking, It May Be an Early Sign of MS. Many symptoms of MS are caused by demyelination. As the Mayo Clinic explains, demyelinating diseases are those that result in damage to the myelin sheath, the protective covering of fatty tissue that surrounds nerve fibers in your brain, optic nerves, and spinal cord—and MS is the most common condition with this feature. “When the myelin sheath is damaged, nerve impulses slow or even stop, causing neurological problems,” the clinic notes. According to the 2015 study, Lhermitte’s sign occurs when the nerves become demyelinated and subsequently miscommunicate. The shock-like sensation is the result of  the “hyper excitable” dorsal column of the spinal cord—a sensory pathway of the central nervous system that communicates sensations of touch and vibration—becoming stretched. This can cause significant pain in MS patients. A 1993 study published in the journal Archives of Neurology notes that this symptom is also associated with spinal lesions in MS patients. “The findings confirm the presumption that a lesion in the posterior columns of the cervical spinal cord is the cause of Lhermitte’s sign in multiple sclerosis,” the team concluded. Though Lhermette’s sign is most commonly associated with MS, it can also have other underlying causes. The Indian Academy of Neurology study points out that Lhermette’s can be the result of chemotherapy, physical trauma, disc herniation, lupus, parasitic invasion in the spinal cord, spinal cord compression, a herpes zoster infection, and more. Speaking with your doctor about your symptoms may allow them to rule out these other conditions in order to reach a diagnosis. RELATED: For more health news sent directly to your inbox, sign up for our daily newsletter. Knowing the other common symptoms of multiple sclerosis may help you reach a diagnosis faster. According to the National MS Society, those with the condition often experience fatigue, walking difficulties, weakness, numbness or tingling, stiffness or muscle spasms, vertigo, dizziness, vision problems, pain, itching, or a squeezing sensation around the torso. MS patients also commonly experience cognitive changes, including difficulty with problem solving, slowed ability to process new information, and emotional changes. Less frequently, MS patients experience problems with speech, swallowing, breathing, hearing, and taste. Some individuals with MS will experience seizures or tremor. Talk to your doctor if you notice these or any other symptoms that you believe could be associated with the central nervous system. RELATED: Selma Blair Just Gave an Update on Her MS Symptoms.