Neuropsychological testing for the assessment of manganese neurotoxicity: A review and a proposal

Background: Manganese exposure can cause neurobehavioral and neurological signs and symptoms. A review of the literature was carried out in order to identify the most sensitive and effective methods to assess these outcomes. Methods: Studies on manganese exposure performed with neuropsychological tests were reviewed using Medline. Test methods, obtained outcomes, and dose-response relationships were considered. Based on the review and additional considerations, a testing battery for adult and children was identified. Results: A total number of 31 studies were reviewed and divided in 18 occupational, 7 environmental, and 6 on children. A large variety of tests exploring motor and cognitive functions and mood were applied. Neurobehavioral effects were dose-dependent in several studies and determined by much lower exposure levels compared to 1 mg Mn/m³ in total dust which is considered to be the minimum concentration able to induce the classical clinical features of "manganism." Although through a wide variety of tests, the observed outcomes support the knowledge that manganese exposure can cause neurobehavioral effects. Motor functions are mainly affected in adults, and cognitive functions and behavior are more affected in children. Conclusions: Literature on manganese neurobehavioral effect is quite consistent, however, further improvement may be achieved by using better structured and more comparable evaluation methods. Based on the analysis of the existing experiences a test battery including tests of motor functions, response speed, cognitive functions, intellectual abilities, mood, and symptom questionnaires is suggested. We recommend that the tests indicated should always be included in future studies as a core battery.