Mercury intoxication: lack of correlation between symptoms and levels.

The incidence of mercury intoxication has decreased considerably because of stricter public health regulations. However, it has not been completely eliminated and should be considered in a child with unexplained tachycardia, hypertension, mood changes, weight loss, and acrodynia. Mercury intoxication can be difficult to differentiate from pheochromocytoma and Kawasaki's disease. Here, the authors report the case of an 8-year-old boy with history of mercury exposure, signs and symptoms suggestive of mercury intoxication, and good response to chelation therapy, but with only mild increase in urinary mercury levels. This case highlights the fact that urinary mercury levels do not necessarily correlate with the severity of clinical signs and symptoms of mercury intoxication.

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

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.

Clinical investigation of the lesions responsible for sensory disturbance in Minamata disease.

To clarify the lesions responsible for sensory disturbance in Minamata disease (MD), we clinically investigated the characteristics of sensory disturbance. In all patients with the classical type MD, two-point discrimination was severely disturbed, but the involvement of superficial sensation was relatively mild. On short-latency somatosensory evoked potential study, the component corresponding to N20 was completely absent with normal N9, N11, and N13 components. Although 14 of 38 chronic MD patients demonstrated intact superficial sensation, 10 of these 14 showed mild to moderate disturbance in two-point discrimination. The two-point discrimination in chronic MD patients was significantly high irrespective of the disturbance of superficial sensation. These findings suggest that the sensory disturbance of MD patients may mainly be caused by a lesion in the sensory cortex rather than in the peripheral nerves. However, other foci could be also responsible for the sensory impairment, since 9 of 38 chronic MD patients showed intact two-point discrimination.