Welders may have a higher-than-average rate of Parkinson’s disease symptoms, the results of a new study suggest.

Researchers found that among more than 1,400 welders from Alabama, the prevalence of Parkinson-like symptoms, including tremor, muscle rigidity and slowed movement, was 7 to 10 times higher than the norm for the general population.

The findings, based on a group of mostly male welders between the ages of 40 and 69 years, are published in the journal Neurology.

In an earlier study of 15 career welders, the same investigators found that the men started suffering Parkinson’s symptoms at an atypically early age - at age 46 on average, versus age 63 in a comparison group of non-welders. That led the researchers to speculate that an as yet unknown toxin in welding fumes might speed the onset of Parkinson’s disease in people who would likely have developed the disease at an older age.

That study, published in 2001, has since been cited in lawsuits against welding-rod manufacturers. Late in 2003, a jury awarded $1 million to a plaintiff who claimed that years of inhaling toxic welding fumes caused his Parkinson’s disease, and thousands of similar lawsuits have since been filed.

But exactly how common Parkinson’s is among welders has been unknown. To find out, Dr. Bruce A. Racette of Washington University School of Medicine in St. Louis and colleagues assessed 1,423 welders, mostly men, who were referred by an attorney for Parkinson’s screening. The researchers compared the welders’ rates of “definite” and “probable” Parkinson’s disease with those found in a previous study of people living in Copiah County, Mississippi.

Overall, 6 percent to 10 percent of the welders were diagnosed with definite Parkinson’s disease, while 13 percent were found to have probable Parkinson’s disease. As mentioned, their rates were 7 to 10 times higher than those in the general male population of Copiah County.

“This study is the largest, to date, implicating welding as a risk factor for parkinsonism,” Racette told Reuters Health. Other studies, he added, have found no such risk, but it’s unclear whether that is related to the smaller size of those study groups.

“We feel that our study is preliminary and requires follow-up with an epidemiology study that incorporates a control group without welding exposure,” Racette said.

Parkinson’s disease is a progressive neurological condition typically marked by four types of symptoms: tremors, muscle rigidity, slowed movement and problems with balance and coordination. The disease occurs when certain brain cells that produce the movement-regulating chemical dopamine are damaged or destroyed.

No one knows what triggers this brain damage, but scientists believe that a number of factors, genetic and environmental, likely play a role. On-the-job exposures to certain chemicals, including pesticides and herbicides, have been linked to Parkinson’s disease, and overexposure to the mineral manganese can lead to Parkinson’s-like symptoms.

The welding process creates fumes that contain manganese, and according to Racette and his colleagues, exposure to the metal “cannot be excluded” as the cause of their patients’ symptoms.

There are many potential toxins in welding fumes, Racette noted, though manganese is the one best recognized as being damaging to nerve cells.

More research, he added, will be needed to clarify exactly what led to the Parkinson’s symptoms seen in these welders.

The current study received partial funding from the Welder Health Fund, created by a group of attorneys to support Parkinson’s disease screening for welders. None of the study authors has received money related the research, according to a disclosure statement in the report.

SOURCE: Neurology, January 25, 2005.