Muscle rigidity, difficulty walking and other motor problems are linked to the development of Alzheimer's disease, says a study in the April issue of the Archives of Neurology.
Researchers at Rush-Presbyterian-St. Luke's Medical Center in Chicago found older people who had a rapid progression of these symptoms were eight times more likely to develop Alzheimer's disease than those with no worsening of such symptoms.
Seniors with slow to moderate progression of the symptoms had a two to five times greater risk of developing Alzheimer's.
"So any progression of this at all was a bad prognostic sign and suggested somehow there are degenerative changes occurring in the brain that must be contributing to these (symptoms)," says study author Robert S. Wilson, a professor of neuropsychology at Rush-Presbyterian.
He and his colleagues studied 824 older Catholic clergy members from about a dozen states. Their average age at the start of the study was 75.4 years old. None of them had any clinical signs of Parkinson's or Alzheimer's at the start of the study.
The clergy members were followed for an average of 4.6 years. Some were studied for as long as eight years; 114 of them developed Alzheimer's during the study.
Once a year, subjects had clinical exams and completed a modified version of a test that measures signs of Parkinson's disease. They also had detailed cognitive testing and were checked for signs of Alzheimer's disease.
The researchers found that motor skill problems worsened in 79 percent of the subjects over the course of the study.
Among that group, those with the most rapid symptom progression had more than eight times greater risk of developing Alzheimer's disease than the people whose symptoms did not worsen. The risk of Alzheimer's more than doubled in those with slight symptom progression and more than tripled in those with moderate progression.
The study also found the rate at which the symptoms worsened was inversely associated with rates of decline on tests that measured cognitive function.
While these symptoms are similar to those seen in people with Parkinson's disease, Wilson says they're not actually caused by Parkinson's.
"We don't think that these people actually are going to go on to have Parkinson's disease. The cause of these motor abnormalities is not securely known, and we think that's going to be an important next step," Wilson says.
There are some theories about what causes the decline in motor ability.
"I think certainly stroke is one thing that's being looked at and we're very suspicious about. We're also looking at diabetes," Wilson says. "Both are things that can increase the risk of Alzheimer's disease as well."
All the people in this study agreed to donate their brains when they die to help further this research. Wilson and his team have collected nearly 250 of those brains so far for analysis.
While this study is interesting, its findings aren't all that surprising, says Bill Thies, vice president of medical and scientific affairs at the Alzheimer's Association.
"Alzheimer's disease is typically worse in people who have more dysfunction, and I think that's what this is sort of indicating here," he says.
Perhaps the most significant aspect of the study is the data showing that annual declines in motor ability are paralleled by reductions in cognitive function, Thies says. "There's a pretty decent relationship that would seem to indicate that the faster you're changing in the motor scores, the faster you're changing in cognition," he says.
While it isn't necessarily a new concept, this study provides actual evidence of a link between motor and mental skills.
"You hear lots of people talk about this relationship. I haven't seen a lot where they've actually measured it. It's been an observation more than anything else. So, from that standpoint, I think it's one of those studies that sort of confirms a commonly held belief," Thies says.