Nigral MRI features of asymptomatic welders.

Abstract Introduction Manganese (Mn)-induced parkinsonism involves motor symptoms similar to those observed in Parkinson’s disease (PD). Previous literature suggests that chronic Mn- exposure may increase PD risk, although Mn-induced clinical syndromes are considered atypical for PD. This study investigated whether asymptomatic welders exhibit changes in the substantia nigra (SN), the key pathological locus of PD. Method Brain MRI data were obtained from subjects in central Pennsylvania participating in welding and/or PD biomarker studies. Diffusion tensor imaging fractional anisotropy (FA; estimate of microstructural integrity) and R2* (estimate of iron and other PD-related brain changes) values in the SN pars compacta (SNc) and SN reticulata (SNr) were compared in welders or PD patients with group-matched controls, and among age-matched subgroups. The SN MRI markers within welders were related to exposure estimates. Results Compared to controls, PD patients had lower FA and higher R2* (ps≤0.018) values in the SNc whereas welders who had chronic but low-level Mn-exposure showed similar FA and R2* values in both SN regions (p>0.240). Subgroup analyses confirmed the overall group comparisons, and also revealed that PD patients had lower SNc FA values compared to age-matched welders (p=0.012). There was a non-linear association of the SN FA with chronic welding exposure (p=0.049). Conclusion Asymptomatic welders did not show nigral imaging changes, suggesting that neurotoxic processes associated with Mn-exposure may be different from those in PD when the exposure level is relatively low. Greater welding duration/level, however, was associated with SN changes, a finding that should be explored further in future studies.