January 04, 2017
By Marilynn Larkin
NEW YORK (Reuters Health) - When exposed to manganese from welding fumes, workers may experience a dose-dependent progression of parkinsonism, researchers say.
Although previous studies have linked welding to parkinsonism, it is not clear whether chronic low-level manganese exposure causes symptoms to worsen over time, Dr. Brad Racette of Washington University School of Medicine in St. Louis, Missouri, and colleagues note in Neurology, online December 28.
To investigate, Dr. Racette and colleagues analyzed medical records of 886 welding-exposed workers (mean age, 46) at three worksites in the Midwestern U.S. from 2006 to 2016. Workers underwent a total of nearly 1,500 examinations by a movement disorders specialist, including 606 follow-up examinations in 398 workers.
One hundred and thirty-five (15.2%) had parkinsonism, with a Unified Parkinson Disease Rating Scale motor subsection part 3 (UPDRS3) score of at least 15 on a scale of zero to 108 points.
The researchers assessed exposure to manganese through a questionnaire about job types and length of time on the job, from which they estimated weighted welding years, factoring in both total duration of welding exposure and the intensity of that exposure.
To convert weighted welding exposure years to estimated mg Mn/m3-year (the standard measurement), they multiplied the weighted welding years by 0.14 milligrams manganese per cubic meter (the estimated average exposure).
Cumulative manganese exposure was associated with a yearly increase in the UPDRS3 of 0.24 (95% confidence interval, 0.10-0.38) for each mg Mn/m3-year of exposure.
Manganese exposure was most strongly associated with progression of upper limb bradykinesia, upper and lower limb rigidity, and impaired speech and facial expression.
The association between welding exposure and progression seemed especially strong in workers who did flux core arc welding in a confined space and workers whose baseline examination was within five years of their first welding exposure.
The authors note that the American Conference of Governmental Industrial Hygienists threshold limit value for manganese exposure is 0.2 mg Mn/m3, based on neurologic health effects. This is higher than the mean time-weighted manganese concentration (0.14 mg Mn/m3) to which they estimated the participants in this study were exposed.
Dr. Racette told Reuters Health by email, "The key finding of this study is that manganese-containing welding fume exposure is associated with progressive parkinsonism at estimated manganese exposure levels that are below current government regulatory limits."
He added, "Our next step is to complete a study in which a subset of these workers undergo brain MRI and PET imaging to determine if these findings are due to damage to the same parts of the brain that are affected in Parkinson's disease."
Dr. Marcia Ratner of Boston University School of Medicine, coauthor of a related editorial, told Reuters Health by email, "The effective differential diagnosis of manganese-induced parkinsonism and Parkinson's disease depends in part on the medical and exposure histories of the patient."
"Thus, this important report by Racette and colleagues reveals a dose-dependent progression of parkinsonism in workers with ongoing exposure which could be mistaken for idiopathic Parkinson's disease if the neurologist fails to effectively inquire about the patient's current risk for exposure to neurotoxicants such as manganese," she said by email.
"Conversely," she added, "because cessation of exposure to manganese is expected to be associated with no further progression and/or with clinical improvement, progression of symptoms following cessation of exposure may reflect the presence of a comorbid neurodegenerative process."
Dr. Melita Petrossian, director of the Pacific Movement Disorders Center at Providence Saint John's Health Center in Santa Monica, California, told Reuters Health by email, "These findings suggest a need for stricter monitoring of manganese exposure in welders, closer assessments of workers, and more consistent use of adequate ventilation and consideration of other mechanisms to reduce manganese particulate matter degeneration."
"This study advanced evidence of progressive parkinsonism brought on by exposure to manganese in the context of welding and occupational exposure," she said. "However, the vast majority of Parkinson's disease patients have no occupational exposure to manganese and the current study does not address extremely low levels of exposure outside of welding exposure."
"Manganese is a naturally occurring element, present in food and in low levels in water," she observed. "There is no evidence that dietary exposure in the typical amount is associated with a higher risk of developing manganism (manganese toxicity), parkinsonism in general, or Parkinson's disease specifically . . . or that Parkinson's disease patients (should) change their dietary intake based on these findings."
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