BARCELONA – Long-term welding work may be a risk factor for developing parkinsonism – perhaps because manganese can travel directly into the midbrain via the olfactory nerve.
Two recent studies suggest a dose-response association, with increased risk as years of exposure accumulate.
©Stana/Fotolia.com
Long-term welding work may be a risk factor for developing parkinsonism.
"Manganese, in particular, has been shown to be a neurotoxin," said Jessica Lundin, a Ph.D. candidate at the University of Washington, Seattle, who presented early findings from a cross-sectional study during a poster session at the meeting. "There is some evidence that it enters via an olfactory route."
The metal is a large component of fumes created by the welding process. According to information provided by the Centers for Disease Control and Prevention, "Prolonged exposure to high manganese concentrations (greater than 1 mg/m3) in air may lead to a Parkinsonian syndrome known as manganism. Chronic exposure to the manganese-containing pesticides is also reported to cause Parkinson-like symptoms"(www.cdc.gov/niosh/topics/welding).
Recent studies have also indicated that long-term exposure to inhaled manganese is associated with neurologic and neurobehavioral deficits, according to the agency. "These effects include changes in mood and short-term memory, altered reaction time, and reduced hand-eye coordination. Affected workers frequently show abnormal accumulations of manganese in a region of the brain known as the globus pallidus."
Ms. Jessica Lundin
Ms. Lundin and her colleagues recruited 581 welders from three U.S. ship-building sites for a 3-year follow-up study. All welders underwent a baseline neurologic assessment by a movement disorders specialist. Assessments in the National Institute of Environmental Health Sciences–sponsored study included the Unified Parkinson’s Disease Rating Scale (motor subsection 3), timed motor tasks, and a questionnaire about occupational history (including prior welding jobs), lifestyle, and medical history, including smoking and neurotoxic exposure, especially to pesticides.
At baseline, individuals in the cohort had a mean age of 45 years and had welded for a mean of 23,000 hours. Individuals in the study were considered to be normal if their UPDRS3 scores were 6 or less; to be mildly affected by parkinsonian symptoms with scores of 6-14; and to have parkinsonism with scores of 15 or higher. At baseline, 199 were considered normal, with a score of 3 or lower; 306 had mild parkinsonian symptoms, with a mean UPDRS3 score of 10; and 76 qualified as having diagnosable parkinsonism with a mean UPDRS3 of 19.
Ms. Lundin compared UPDRS3 scores with total hours of welding exposure at baseline. She found a linear association, with risk increasing along with total exposure.
Subjects considered normal had a mean age of 41 years and a total exposure of 18,300 hours. Those with mild parkinsonian symptoms were a mean of 46 years old and had a mean total exposure of 25,100 hours. Those with parkinsonism had a mean age of 48 years, with a mean total exposure of 26,800 hours.
The prevalence ratio also rose with increasing exposure. Those with a total of less than 2,900 hours were considered the reference group, with no increase over expected background rates. The prevalence of parkinsonism increased by 20% for those with a total exposure of 2,900-9,600 hours, by 40% with 9,600-26,400 hours of exposure, and by 60% with more than 26,400 hours.
None of these baseline differences in UPDRS3 scores and prevalence of parkinsonism were statistically significant, but they provided a trend strong enough to justify the 3-year follow-up, Ms. Lundin said in an interview. "We will follow this group to determine incident cases of Parkinson’s symptoms and symptom progression. We also have some industrial hygienists working with us to collect samples of manganese [on surfaces] in the shipyard and in the air."
Further work will include comparison to a nonwelding reference group, as well as blood samples indicating exposure to manganese, cadmium, lead, aluminum, copper, and other metals. These analyses will be part of a multivariate regression that will control for age, she added.
The pallidal index, an imaging outcome, was one of the primary end points of a separate study of welding and Parkinson’s disease (Neurology 2011;76:1296-1301).The index is a ratio of T1-weighted imaging signal in the global pallidus, compared with a reference region of white matter.
Primary investigator Dr. Susan Criswell, Washington University, St. Louis, conducted an imaging study of 20 asymptomatic welders, also primarily recruited from shipyards. These were compared to 20 subjects with idiopathic Parkinson’s disease and 20 normal controls. Positron emission tomography with 6-[18F] Fluoro-L-dopa (FDOPA) measured dopaminergic presynaptic nerve terminal dysfunction in different brain regions in all of the participants.