Pesticide Tied to Sleep Problem

REM sleep behavior disorder, a rare condition, appears to share some risk factor associations such as occupational pesticide exposure with Parkinson’s disease.

A rare sleep disorder characterized by disturbances of rapid eye movement (REM) sleep shares some environmental risk factors with Parkinson’s disease, an international case-control study suggested.

For example, occupational pesticide exposure has been clearly linked with Parkinson’s disease, and in this study patients with REM sleep behavior disorder were twice as likely to have been exposed to pesticides as controls, according to Ronald B. Postuma, MD, of McGill University in Montreal, and colleagues.

But other environmental risk factors common to Parkinson’s disease do not come in to play in the sleep disorder. For instance, patients who don’t drink coffee have consistently been shown to be at higher risk for Parkinson’s disease, but no such association was found in patients with the REM sleep disorder, the researchers reported online in the July 31 issue of Neurology.

REM sleep behavior disorder is characterized by the absence of muscle atonia usually present during REM sleep and by “dream enactment,” during which disruptive and aggressive behaviors can occur.

The condition has been linked with the later development of Parkinson’s disease and Lewy body dementia, and may be a preclinical sign or a specific subtype.

“Idiopathic [REM sleep behavior disorder] as a syndrome has an unusual status — it exists both as an independent sleep condition and as a prediagnostic marker of synuclein-mediated neurodegenerative disease,” Postuma and colleagues explained.

Because of the rarity of the disorder — the prevalence has been estimated to be 0.4% to 0.5 percent in adults — little has been known about risk factors.

So the international REM Sleep Behavior Disorder Study Group has combined the patient populations from 13 centers in 10 countries, and Postuma and colleagues have analyzed behavioral and exposure risk factors for 347 patients with the disorder.

A control group consisted of 218 patients with other sleep disorders and 129 healthy volunteers, matched for age and sex.

Mean age of the cases was 68 years and 81 percent were men.

Overall, factors that were associated with the REM sleep disorder were pesticide exposure, cigarette smoking, head injury, lower educational achievement, and working on a farm.

Unlike Parkinson’s disease, where nonsmokers typically have been considered at greater risk for the disorder, in this analysis patients who had ever smoked cigarettes had an increased risk for the REM sleep disorder compared with controls.

Current cigarette smokers also were at elevated risk.

“One of the most intriguing aspects of this work is the picture of similarities and differences among risk factors,” observed Christian Guilleminault, MD, of Stanford University in Palo Alto, Calif., and colleagues.

“While pesticide exposure appears to be a risk factor for both disorders, smoking, for example, which is protective for [Parkinson’s disease], is a risk factor for [REM sleep behavior disorder],” Guilleminault’s group wrote in an accompanying editorial.

Patients with the REM disorder were more likely to have experienced a head injury with loss of consciousness.

Additional factors associated with the sleep disorder included the number of years of schooling, and farming as an occupation.

Other types of jobs such as mining and teaching were not associated with the disorder, while a borderline relationship was seen for welding.

In a sensitivity analysis, the association between certain factors such as smoking, head injury, and farming and the REM disorder was stronger when affected patients were compared with healthy controls than when they were compared with patients who had other sleep disorders. That may have been related to the “healthy volunteer effect,” in which people who volunteer to participate in research may be more health-conscious in general, the authors noted.

However, overmatching with controls who have other sleep disorders could have occurred if they shared risk factors with the REM disorder, the investigators also noted.

Limitations included the cross-sectional design of the study and the possibility of recall bias, particularly for patients who may have preclinical dementia.

There also may be differences in patients with REM sleep behavior disorder who are referred to specialty clinics and those who are never seen at such centers, so a population-based study could provide additional useful information, the researchers noted.

By Nancy Walsh