Working around PD.

Jobs that involve the use of certain common solvents may put people at risk for developing Parkinson disease at an earlier age and having more severe symptoms throughout the course of the disease, according to a study in the 12 September 2000 issue of Neurology. This is the first large clinical study to find evidence of a link between Parkinson disease and hydrocarbon exposure.

Parkinson disease is a progressive disease of the nervous system that can cause trembling or shakiness, rigid muscles, slowed movement, and impaired balance. It usually affects people in their 50s or older, although the National Institute of Neurological Disorders and Stroke has stated that physicians are noticing more cases among younger patients.

The study, conducted at the Parkinson Institute in Milan, Italy, included 188 patients with Parkinson disease who also reported significant past exposure to hydrocarbon solvents, found in many common products such as paints, glues, and petroleum derivatives. These patients were matched by sex and duration of disease with 188 patients who reported no such history of exposure. The researchers found that people in the exposed group were an average of 3.4 years younger than those in the nonexposed group at the time of diagnosis. In addition, the severity of symptoms was shown to be directly related to the degree of hydrocarbon exposure.

Over 90% of people in the exposed group fell into one of nine job classifications: petroleum, plastics, and rubber workers; painters, lacquerers, and furniture workers; engine mechanics; typographers and lithographers; leather workers; chemists; textile workers and weavers; farmers; or refrigerating system workers. The study authors note that most on-the-job exposures occurred in family-run businesses, where they found safety measures tended to be less stringent and more difficult to enforce.

One possible limitation of the study is that it relied mainly on self-reports of past exposures, which are subject to the vagaries of memory. However, the highly significant correlation between degree of exposure and severity of symptoms would tend to support the accuracy of the patients' self-reports. Also, although many people were already retired by the time of diagnosis, blood and urine samples taken from the 15 patients who said they were still exposed to hydrocarbons invariably yielded high concentrations of the compounds. Another possible weakness is that the study considered all hydrocarbons together, says Robert C. Feldman, a professor of neurology at Boston University. Analyses of products used by the still-exposed patients along with measurements of these substances in their blood and urine revealed mixtures of a wide range of possibly interacting chemicals, which makes it impossible to sort out the individual effects of particular compounds.

According to Feldman, there are insufficient data to indicate whether Parkinson disease was a direct toxic effect or an induced condition in genetically susceptible people. Nevertheless, the study may be an important new piece in the Parkinson puzzle by suggesting that hydrocarbon exposure is one of the contributing environmental factors.