Analysis of Rapid Alternating Movements in Cree Subjects Exposed to Methylmercury and in Subjects with Neurological Deficits

• Published in: Environmental research Vol. 80; no. 1; pp. 64 - 79
• Main Authors: Beuter, Anne, de Geoffroy, Anne, Edwards, Roderick
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.01.1999; Elsevier
• Subjects: Biological and medical sciences; Case-Control Studies; Chemical and industrial products toxicology. Toxic occupational diseases; Environmental Exposure - adverse effects; Environmental Exposure - analysis; Hair - chemistry; Humans; Indians, North American; Medical sciences; Metals and various inorganic compounds; methylmercury; Methylmercury Compounds - adverse effects; Methylmercury Compounds - analysis; Middle Aged; Movement - drug effects; movement disorders; Movement Disorders - etiology; Movement Disorders - physiopathology; neurological deficit; Parkinson Disease - physiopathology; Psychomotor Performance - drug effects; quantitative measure; Quebec; rapid alternating movements; Sensitivity and Specificity; Toxicology; Canada; North America; America; Quebec; methylmercury; quantitative measure; rapid alternating movements; movement disorders; neurological deficit; Amerindian; Human; Nervous system diseases; Toxicity; Neuropsychological test; Manual activity; Alternate motion; Heavy metal; Motility disorder; Body movement; Upper limb; Measurement method; Neurological disorder; Mercury
• ISSN: 0013-9351; 1096-0953
• DOI: 10.1006/enrs.1998.3885

To quantify rapid alternating movements (RAMs) we used a simple prototype developed in our laboratory that requires the subject to rotate two hand-held foam spheres connected to optical encoders via flexible rods. Ninety-six participants, including 30 control subjects, 36 Cree subjects exposed to methylmercury, 21 subjects with Parkinson's disease, 6 subjects with cerebellar deficits, and 3 subjects with essential tremor, were involved in the study (though data for 5 were later removed). Twelve characteristics were developed and calculated from the raw data. Conditions examined included two hands at natural cadence (NC2), right and left hands separately at fast cadence (FCl), and both hands at fast cadence (FC2). Two ratios (FC2/NC2) and (FC2/FC1) combining these conditions were also examined. Test–retest reliability was >0.80 for most characteristics but was <0.70 for some characteristics, especially in the conditions executed at normal cadence. Correlations between characteristics and numbers of outliers with respect to the control group distribution were used to reduce the set of characteristics from 12 to 7 (i.e., duration, range, maximum slope, similarity in shape, smoothness, sharpness, and coherence). ANOVAs on the three largest groups generated significant results for most characteristics in the three conditions and the two ratios for Cree subjects and subjects with Parkinson's disease. ANOVAs on 3 age-matched groups (n=6) suggest that methylmercury affects the performance of the Cree subjects with the higher exposure, especially in terms of smoothness, sharpness, and coherence. These preliminary results suggest that this test is sufficiently specific and sensitive to characterize the performance of different groups of subjects. Ratios tend to improve discrimination for Cree subjects in a few characteristics but not for patients with Parkinson's disease.