Differences in frequency of finger tremor in otherwise asymptomatic mercury workers.

Abstract

Tremor was measured from the index finger during low force, position holding in 18 control subjects and 18 battery workers with low level exposure to mercury. All workers were asymptomatic on clinical neurological examination. No differences were found in average tremor amplitudes between the groups, but statistically significant abnormalities in tremor frequency distribution existed. Tremor power spectra in the group of mercury workers were shifted toward the higher frequencies and compressed into narrow frequency peaks. These results suggest that measurements of finger tremor that evaluate the frequency distribution can produce a higher diagnostic yield than traditional visual We used a measurement system specifically designed to be sensitive to subtle amplitude and frequency features by being sufficiently lightweight and pliable to accurately track fine vertical movement oscillations. Subjects were positioned so that tremor was measured from the isolated index finger of the supported hand, a low mass limb segment less likely to damp oscillations, and with less intersubject anthropometric variability in size, weight, and elasticity than the extended hand, forearm, or entire upper extremity.8 19 The natural resonant frequency of the index finger has been determined to be around 25 Hz, well outside the range of the neuromuscular frequencies of interest in tremor measurement (4-16 Hz).20We evaluated finger tremor associated with precision movement in a group of 18 asymptomatic mercury workers and age matched controls. All the mercury workers received a special medical examination specifically designed to search for signs and symptoms of mercury toxicity. Urine samples of workers were also evaluated for mercury content. The purpose of the investigation was to compare the sensitivity and specificity of tremor measurement to conventional clinical examination procedures. We were also interested in determining whether certain features of tremor frequency were shared by the mercury workers and how they were related to indicators of exposure. Methods SUBJECTSThe 18 study subjects were employed by one firm and worked in one of three plants producing cylindrical, alkaline magnesium batteries and button type mercury battery cells. Their mean age was 33-3 (SD 12-6, range 20-57 years). Fourteen were men and four were women. The mean duration of exposure 838 copyright.

Neurotoxic Effects in Workers of the Clinical Thermometer Manufatcure Plant

“…Some of the study outcomes support the findings concerning the alterations of neuroendocrine secretion and motor coordination at very low occupational exposure levels of inorganic mercury, below the current biological exposure index [21]. They also indicate that abnormal tremors and other neurological effects may even occur in lower urinary mercury concentrations [22]. Nevertheless, other studies have disclosed that exposure to high concentrations of mercury may produce fatalities and devastating neurological damage among adult survivors [23].…”

Effects of mercury vapor exposure on neuromotor function in Chinese miners and smelters

“…The increased tremor at a high frequency (i.e., 10-14 Hz) is almost accordant with the Wndings provided by Chapman et al (1990) and Verberk et al (1986). Likewise, younger patients with essential tremor exhibit tremor frequencies in the range of 8-12 Hz (Elble 2005).…”

“…Such increased tremor has been conWrmed by many previous reports (Albers et al 1988;Biernat et al 1999;Chapman et al 1990;Fawer et al 1983;Frumkin et al 2001;McCullough et al 2001;Netterstrøm et al 1996;Roels et al 1982); in an exceptional case, Boogaard et al (1996) failed to Wnd any signiWcant diVerence in intentional tremor between mercury-exposed workers with the median UHg of 17 (range 3.5-71.9) g/g Cre and the control subjects with the median UHg of 2 g/g Cre. Additionally, tremor in patients with Minamata disease has been reported to be diVerent from physiological tremor and other pathological tremors from the viewpoint of frequency and amplitude (Yamanaga 1983), while the toxico-kinetics and -dynamics diVer between elemental mercury and methylmercury.…”

“…By contrast, many researchers, except for one group (Boogaard et al 1996), have reported that hand tremor is associated with mercury exposure (Albers et al 1988;Echeverria et al 1998;Fawer et al 1983;Langolf et al 1978;McCullough et al 2001;Netterstrøm et al 1996;Roels et al 1982;Wood et al 1973). Given the spectral analysis of hand tremor, the tremor frequencies aVected by mercury vapor have been observed at 6.6-10 Hz (Biernat et al 1999), at 8-12 Hz (Verberk et al 1986), and at 10-15 Hz (Chapman et al 1990). Actually, since current risk assessment of mercury vapor is based on the tremor toxicity (Agency for Toxic Substances and Disease Registry 1999), other adverse eVects on the nervous system may also be relevant.…”

Occupational and Environmental Toxicology of Mercury and Its Compounds.

“…2) Increased complaints of tiredness, memory disturbance and other symptoms have been reported in selfadministered questionnaires 34) 3) Subclinical finger tremor has been observed using apparatus analyses 33,36,37) 4) Slower and attenuation of power spectrum of EEG 38) 5) Impaired performance in neurobehavioral or neuropsychological tests 39) …”