![]() ![]() The higher Cf in welders and ET compared to PD subjects was confirmed by analysis of energy distribution into two frequency bands, 3–6.5 Hz and 6.6 to 10 Hz. However, the Cf of the rest tremor in the ET group was significantly lower than the Cf of the rest tremor of the welders. The mean Center Frequency (Cf) of the postural tremors was significantly higher in welders and ET group compared to PD subjects ( Figure 2). Measures derived from acceleration data were based on the Fourier power. Fast Fourier Transform (FFT) analysis was used to determine the normalized power distribution of the tremor in the frequency band 0.9 Hz to 15.0 Hz. The hand vibrations were recorded and displayed in real-time against a time axis plot on the computer screen. The pen was held with the long axis parallel to the ground. For the postural tremor the pen was held in a writing posture but the arms were extended anteriorly, level with the shoulders. The pen was held with the first three digits of the hand in a writing posture, but with the hand slightly supinated so the long axis of the pen was parallel to the ground. Subjects were asked to sit with their hands comfortably resting on their lap (proximal thighs) with one hand holding a pen-like stylus that contains a biaxial micro- accelerometer. The accelerometer utilized in this study is a component of a portable-PC based test system (Catsys System) to measure coordination reaction time, tremor and postural sway or stability (Danish Product Development, Ltd). The syndrome of manganism was inferred from the appearance of slowness, rigidity, tremors (both resting and postural), cramping or dystonia of limbs, upper motor neuron signs, and behavioral disturbances (irritability, depression) in the context of chronic exposure to welding fumes. As an exploratory study, JSR recorded tremor with a portable accelerometry system (CATSYS, LTD) in a sample of 37 welders or welding assistants each of whom was examined independently on the same day (by PN and JSR) and given a consensual diagnosis of probable manganism. Subjects with extrapyramidal signs (slowness of movement, rigidity, tremors) were then examined in subsequent visits over three years by two neurologists (PN, JSR) with expertise in Movement Disorders. The majority of the subjects who had undergone the initial screening for neurologic symptoms typically did not have extrapyramidal features, but rather exhibited signs consistent with peripheral neuropathies, radiculopathies, stroke, and occasionally demyelinating disease or motor neuron disease (see Flow Chart Figure 1). A team of physicians conducted screening examinations following a simple protocol designed to detect any neurologic abnormality. These subjects were self-selected by responding to advertisements that listed a number of symptoms and signs associated with manganese toxicity. Selection of SubjectsĪpproximately 20,000 individuals who worked as welders or assistants in shipyards and refineries were screened for neurologic abnormalities in a union-organized effort supported by a legal consortium over a period of five years. The practical goal was to assess whether differences in resting and postural tremor intensities and energy distribution across the spectrum of oscillation frequency could be useful in differentiating tremor in welders diagnosed with “manganism” from IPD and ET. The objectives of this retrospective study were (a) to characterize and analyze the tremor of welders and associated workers with a history of exposure to manganese in the workplace and (b) to compare the welders’ tremor parameters with those of de novo PD patients who had not been treated with anti-PD medications and to a group of patients with postural tremors, Essential Tremor (ET). ![]() ![]() To explore and quantify parameters of tremor in welders, a quantitative analysis of previously recorded accelerometric data was performed. Hand tremor that worsens with activity, or with arms extended, is more typical in cases of manganism. A tremor “at rest” is considered a classic sign of IPD, while such a tremor is reported as an inconstant clinical sign in manganism. ![]()
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