Manganese-induced parkinsonism, Parkinson's disease and welding

Excessive manganese exposure may induce a neurological syndrome similar to Parkinson's disease (PD), called manganism. However, close observation of manganism patients reveals a clinical disease entity different from PD, not only in the clinical manifestation and therapeutic response, but also in the neuroimaging studies, such as magnetic resonance images (MRI), positron emission tomography (PET), and dopamine transporter images (DAT), and in the neuropathological findings. The differences in the clinical manifestations between manganism and PD include in the former less-frequent resting tremor, more frequent dystonia, gait en bloc, and a wide-based and characteristic cock-walk gait. In PD, a persistent focal asymmetry is noted, whereas in manganism there is a high degree of symmetry. However, a unilateral cock-walk gait and asymmetric dystonia are also found in chronic manganism. Therefore, symmetry is not a good differential clue between manganism and PD. A failure to achieve a sustained therapeutic response is noted in manganism. Neuroimaging studies may distinguish manganism from PD. The findings in manganism are hyperintensity in the basal ganglia on T1-weighted MRI scans, and normal 6-fluorodopa PET and DAT scans. Neuropathologically, PD is associated with neuronal loss in the substantia nigra pars compacta and locus ceruleus, and the presence of Lewy bodies, whereas in manganism, gliosis mainly is limited to the globus pallidum and substantia nigra pars reticularis, with an absence of Lewy bodies. Furthermore, manganism has a clinical course different from PD; in long-term follow-up, manganism patients show a prominent deterioration in the parkinsonian symptoms in the initial 5-10 years, followed by a plateau in the following 10 years. In the most recent few years, the possible potential risk of inhaling welding fumes to accelerate the onset of PD or induce PD has been raised. Previous studies have not provided adequate evidence to support the relationship between welding and PD because of a lack of exposure data and selection bias with the patients. However, welding fumes may contain various neurotoxic substances in addition to manganese such as iron which may increase oxidative stress. Further investigation is warranted.