PD develops over time as neurons in certain areas of the brain that control muscle movement slowly waste away, according to background information in the article. The degeneration occurs in areas that produce a neurotransmitter known as dopamine. Typical symptoms of PD--including severe tremors, rigidity and slow movements--begin when the brain loses more than half of its dopamine production ability.
Lonneke M. L. de Lau, M.D., and colleagues at the Erasmus Medical Center, Rotterdam, the Netherlands, hypothesized that individuals who were developing PD might experience some other, milder symptoms before clinically recognizable symptoms of PD occur. They examined 6,038 elderly people who did not have PD or dementia. The participants answered questions about their motor skills, including whether they had experienced stiffness, tremors, falling, slowness or a feeling of imbalance. More than half of them reported at least one of these complaints. They were then assessed for PD at two follow-up visits and their medical records were analyzed.
Over the course of the study, which followed participants for an average of 5.8 years, people who had initially reported stiffness, tremors or imbalance were more likely to develop PD than those who had not. Of the 56 people who developed PD during the study, 71.8 percent had reported at least one motor complaint and 41 percent at least two.
"Our findings support the notion that clinically manifest PD is preceded by a preclinical phase that is not entirely asymptomatic," the authors report. "Subjective complaints related to motor function might indicate a very early phase of not-yet-diagnosable PD during which dopamine loss is not sufficient to produce overt typical PD symptoms but may result in subtle signs that are very mild or only intermittently present and therefore not likely to be detected in routine screening or examination."
Since such a large percentage of elderly people report these motor symptoms and a relatively small percentage of them go on to develop PD, it's unlikely that screening for these complaints alone would be effective in detecting the disease, the authors report. However, as researchers continue work to pinpoint biological markers of PD, assessing these types of complaints might help narrow down candidates for brain imaging, psychological testing or other methods of early diagnosis, they conclude.
(Arch Neurol. 2006; 63: (doi: 10.1001/archneur.63.3.noc51312). Available pre-embargo to the media at www.jamamedia.org)