St. Louis, Jan. 22, 2001 -- Scientists have identified the first clue that welding might trigger the early onset of Parkinson's disease (PD). A research team led by neurologist Brad A. Racette, M.D., found that 15 professional welders developed typical clinical and neurological signs of the disease an average of 15 years earlier than the general population. The study is featured in the January issue of the journal Neurology with an accompanying editorial.
"This research doesn't prove that welding causes PD," explains Racette, an assistant professor of neurology at Washington University School of Medicine in St. Louis. "But it's suspicious that the majority of these patients had a much younger age of onset. Our theory is that we have identified a group of people who probably would have developed the disease eventually, but something in the welding environment caused them to develop symptoms earlier."
PD is a progressive movement disorder that affects more than 1 million Americans. It is characterized by slowness of movement and tremors that affect one side more than the other. Although genetics can account for some cases, 80 percent of PD patients lack a family history of the disease.
Scientists therefore have hypothesized that environmental factors are largely responsible. However, no such factors have been identified.
One clue, though, is that manganese miners are susceptible to a condition called manganism because they inhale large amounts of the mineral manganese. The disease is classified as a Parkinson syndrome because it bears a resemblance to PD. But both the symptoms and brain pathology are significantly different. Welding fumes also contain high levels of manganese. But when a young welder walked into Racette's office and said he was suffering from manganism, Racette knew something was fishy.
"Manganism is a very different disease. To me, this patient clearly looked as if he had PD," Racette says.
He soon discovered a lore that welding may lead to PD; material data safety sheets even list the disease as a possible hazard. But there is little scientific evidence to back up the idea. Racette and colleagues therefore set out to determine whether welding is in fact an environmental contributor to PD. They identified 15 professional welders among patients in the school's Movement Disorders Center. Then they compared the welders' medical history and clinical symptoms with those of control PD patients.
They found no clinical differences between the welders and typical PD patients. The two groups had the same severity and frequency of symptoms and responded similarly to levodopa, a drug used to treat PD. The only statistically significant difference was average age of onset: 45 for the welders or 15 years younger than for the control group.
Racette and colleagues also imaged the brains of two of the welding patients and 13 control patients. People with PD typically have lower levels of a neurotransmitter called dopamine in certain regions of their brain. Using a technique called fluorodopa positron emission tomography (FDOPA PET), the researchers determined how much dopamine the brain could take up. With that information, they assessed the extent of Parkinson-like deterioration. The FDOPA PET scans revealed no significant difference between the welding and control groups. Therefore, the welders appeared to have typical PD. "These results are really exciting because we may soon be able to identify the first environmental cause of PD," says Racette. "Our first goal is to show that welding truly does cause this disease. Then we can figure out which aspect of welding is responsible." This information, Racette argues, will help determine whether welders should take precautionary measures and also will help researchers begin to unlock the underlying cause of this debilitating disorder.
In the editorial that accompanies the paper, Canadian neurologist Ali H. Rajput, M.B.B.S., F.R.C.P.C., likens the search for environmental causes of PD to looking for a needle in a haystack. "By narrowing the focus to one environmental group, Racette et al. have chosen a smaller stack and, therefore, have a greater chance of finding whether there is a needle or not," he says.
Racette BA, McGee-Minnich L, Moerlein SM, Mink JW, Videen TO, Perlmutter JS. Welding-related parkinsonism: Clinical features, treatment, and pathophysiology. Neurology, 56, 8-13, Jan. 9, 2001.
Funding from the National Institutes of Health, the American Parkinson's Disease Association, the Charles A. Dana Foundation and the McDonnell Center for the Study of Higher Brain Function supported this study.
The full-time and volunteer faculty of Washington University School of Medicine are the physicians and surgeons of Barnes-Jewish and St. Louis Children's hospitals. The School of Medicine is one of the leading medical research, teaching and patient care institutions in the nation. Through its affiliations with Barnes-Jewish and St. Louis Children's hospitals, the School of Medicine is linked to BJC Health System.