The study, which focused on people with benign or inactive MS, was published in an online issue of Neurology, the medical journal of the American Academy of Neurology.
People with benign MS are those who remain "fully functional" after 15 or more years from disease onset.
Nearly 30 percent of the participants experienced significant worsening of the disease during the five years. People who failed more than two out of 10 cognitive tests were 20 percent more likely to progress over time. Men with benign MS were nearly three times more likely to later experience signs of MS compared to women. People with more brain lesions detected on scans were also more likely to develop signs of the disease.