Almost one in 1,000 people in the United States has MS, according to the review.
"Our estimate of MS prevalence is about 50 percent higher than a comprehensive review from 1982," says researcher Deborah Hirtz, M.D., in an American Academy of Neurology news release. "Whether this reflects improvement in diagnosis or whether incidence is actually increasing deserves further study," says Hirtz, who works at the National Institute of Neurological Disorders and Stroke.
Hirtz and colleagues analyzed about 500 studies published from 1990 to 2005 to track 12 neurological disorders. Their findings appear in the Jan. 30 issue of Neurology.
The researchers tracked the prevalence (total number of cases) of the following conditions:
These conditions aren't necessarily the most common neurological disorders, note Hirtz and colleagues. For instance, they didn't track sleep disorders, chronic pain, or mental retardation. And though autism and cerebral palsy are lifelong conditions, data were only available for cases in children.
Besides the rise in MS prevalence, the researchers also note a "possible" increase in nonfatal stroke and a "substantial" rise in Alzheimer's disease, compared with the 1982 review. Those trends are likely due to America's aging population and better diagnosis, according to the review.
Traumatic brain injuries are down by about half since the 1982 review.
"It is likely that this reflects more restrictive hospital admission criteria, although improvements in motor vehicle safety may also contribute," write Hirtz and colleagues.
They note no major changes in rates of cerebral palsy, epilepsy, migraine, ALS, or Parkinson's disease. Previous estimates weren't available for autism spectrum disorders or Tourette's syndrome.
Past data were "too sparse" to track trends in spinal cord injury, the researchers say.
Since high-quality U.S. data on most disorders were lacking, the researchers often applied data from other countries to the U.S. population. That approach isn't ideal, the researchers admit. They call for better studies to track neurological disorders in the United States.
Still, they say, their findings show "the burden of neurologic illness affects many millions of people in the United States."
SOURCES: Hirtz, D. Neurology, Jan. 30, 2007; Vol. 68: pp. 326-337. Albert, S. Neurology, Jan. 30, 2007; Vol. 68: pp. 322-323. News release, American Academy of Neurology.
By Miranda Hitti
Reviewed by Louise Chang, M.D