Clinically isolated syndrome (CIS) is one of the first clinically visible and evident symptoms of multiple sclerosis (MS), a neurologic condition in which a person's immune system mistakenly attacks myelin, the protective covering on nerve fibers in the brain and spinal cord. About 85 percent of people with MS experience CIS first, according to the journal Multiple Sclerosis and Related Disorders.

Symptoms of CIS typically affect the eyes and limbs, with patients developing new, painful vision loss or double vision; loss of sensation of any limb or one side of the body or both legs; paralysis; dizziness; problems with their gait; or imbalance. A neurologist's examination can help confirm that the patient has lost vision, which typically affects one eye; has impaired eye movement or balance; has lost muscle strength or sensation in their limbs; or has started walking abnormally.

Patients can expect the evaluation to include an MRI of their brain or spinal cord so the neurologist can look for lesions typical of MS. Lesions represent damaged areas of the nervous system—especially involving the myelin, axons (the part of nerve cells that conducts impulses), and surrounding tissue—and look like scars on the brain or spinal cord. The abnormal immune system that begins to attack the brain and spinal cord in MS is the main driver of this damage.

Neurologists treat CIS like they do relapsing MS, a type of the disease in which patients alternate between periods of new or worsening symptoms and periods of recovery or remission. People with CIS have numerous treatment options, as the U.S Food and Drug Administration has approved more than 25 disease-modifying therapies (drugs that target a condition's underlying cause instead of just the symptoms in the hope of slowing down or changing the disease progression). They include oral medications such as dimethyl fumarate (Tecfidera), fingolimod (Gilenya), siponimod (Mayzent), and teriflunomide (Aubagio). Drugs delivered via injection or infusion also are available.

People whose MRIs show that they have brain lesions similar to those seen in MS have a 60 to 80 percent chance of experiencing a second neurologic event and being diagnosed with MS, according to the National Multiple Sclerosis Society. The risk is lower—just 20 percent—if an MRI does not reveal brain lesions in a patient with CIS.

Because of this risk of eventually developing MS, neurologists monitor patients for new lesions and MS attacks. A patient who has both CIS symptoms and an MRI that shows potential evidence of MS would undergo a spinal tap to confirm whether they have MS.

Some people have a greater risk of developing CIS, including younger White women, people who were obese at a younger age, and those who have had a vitamin D deficiency. Keeping kids and young adults healthy with the goal of having a normal body weight and optimal vitamin D levels in addition to not smoking may protect them against developing CIS and, in turn, MS.

Clinically Isolated Syndrome Resources

• Multiple Sclerosis Association of America
• Multiple Sclerosis Foundation
• National Multiple Sclerosis Society

Dr. Yadav is interim chair and professor of neurology, endowed professor for MS research, head of the division of MS and neuroimmunology, and director of the MS/neuroimmunology fellowship program at Oregon Health & Science University. She also is a staff neurologist, researcher, and assistant director of clinical care at MS Centers of Excellence—West in the Veterans Affairs Portland Health Care System