Characteristics of hand tremor and postural sway in patients with fetal-type Minamata disease

Abstract

-About forty certified patients aged around 50 years old existed as living witnesses to fetal-type Minamata disease (methylmercury poisoning due to in utero exposure) in Minamata, Japan in 2006. Computerized hand tremor and postural sway tests with spectral analysis were conducted for 24 of them and in matched control subjects to examine the pathophysiological feature of neuromotor function. The tremor intensities of the patients with fetal-type Minamata disease were significantly larger than those of the 67 controls at every frequency band for both hands. In the patients, proportions for intensity at 1-6 Hz of both hands were larger, but those of the intensity at 6-10 Hz were smaller compared with the controls. The center frequency of a tremor was significantly lower in the patients than in the controls. Only eight males of the 24 patients were examined to evaluate postural sway because of extremely low scores in activities of daily living in the remaining. Most of the postural sway parameters obtained with eyes open and closed were significantly larger in the patients than in the male controls. Likewise, Romberg quotients of postural sway in anterior-posterior direction were significantly higher in the patients. In conclusion, the patients with fetal-type Minamata disease of our study showed a larger tremor of low frequency at less than 6 Hz and postural instability. Spectral analyses of computerized hand tremor and postural sway are suggested to be useful for assessing the pathophysiological change, related to a lesion of the cerebellum, resulting from prenatal methylmercury exposure.

Mercury and Mercury-Containing Preparations: History of Use, Clinical Applications, Pharmacology, Toxicology, and Pharmacokinetics in Traditional Chinese Medicine

“…Cases of severe and even fatal methyl mercury poisoning date back to England in the 1860s, accidents in Iraq in 1971 and 1972 killed hundreds of people and caused thousands of serious poisoning incidents and industrial discharges of methyl mercury in Minamata bay and the Agana River in Japan resulted in the accumulation of toxic substances in fish ( Jackson, 2018 ). In the Minamata Bay area, infants are beginning to develop serious illnesses similar to cerebral palsy, and fetuses are considered more sensitive to methylmercury than adults ( Iwata et al, 2016 ).…”