Researchers from the Mayo Clinic, Sun Health Research Institute and the Arizona Parkinson's Disease Consortium studied how patients with Parkinson's disease transition to an immediate state of cognitive problems before developing dementia.

Dementia is associated with Parkinson's in up to 40 percent of patients.

In the study, led by Mayo Clinic Dr. J.N. Caviness in Scottsdale, Ariz., subjects underwent testing for problems with memory, planning and abstract thinking ability, attention, language and visuospatial function. Researchers found 22 percent of subjects had significant cognitive problems in one or two areas, but not severe enough to be diagnosed with dementia.

"The value in identifying such a state of mild cognitive impairment is that this intermediate stage could provide clues about how cognitive ability can deteriorate in Parkinson's disease," said Caviness. "Understanding this intermediate state of cognitive impairment could help in finding treatments for cognitive problems in Parkinson's."

The study appeared in the July 15 issue of the journal Movement Disorders.