Increase in signal intensities on T1-weighted magnetic resonance images inasymptomatic manganese-exposed workers

Objectives. To clarify the clinical significance of increased signal intens ities on T1 weighted magnetic resonance imaging (MRI) we performed a large- scale epidemiological study on asymptomatic manganese (Mn)-exposed workers with its focus on MRI. Methods: We randomly selected 121 male workers out o f a total of 750 workers including Mn-exposed, non-exposed manual, and non- exposed clerical workers in the factories. We studied environmental and bio logical monitoring, neurological examination, and MRI. Results: The proport ion of workers with increased signal intensities among the exposed the non- exposed manual workers, and the non-exposed clerical workers was 46.1%, 18. 8%, and 0%, respectively. Especially, 73.5% of the welders showed increased signal intensities. In no subject, were clinical signs of manganism observ ed. The pallidal index correlated with blood Mn concentration. Conclusion: Increase in signal intensities on the T1-weighted image reflect recent expo sure to Mn, but not necessarily manganism. At which increase of signal inte nsity, the progression of manganism from Mn exposure occurs, remains to be solved. (C) 1999 Intox Press, Inc.