Neurological and electrophysiological examination on workers exposed to mercury vapors

The authors carried out neurological examination, visual evoked potentials (VEP) examination, and electromyography (EMG) on 77 workers, aged 21-61 yrs, who were exposed occupationally to Hgo vapors for 1-20 yrs (mean 9 yrs). The mean air-borne concentration of Hgo was 0.25 mg/m3 (range 0.02-1.00 mg m3), and the mean Hg urinary concentration was 0.21 mg/l (range 0.02-0.77 mg/l). Symptoms of erethism (generally accepted as a typical sign of micromercurialism) were reported in about 80% of the workers. The static tremor of fingers (in 25%), and the absence of ankle jerk (in 20%) were the most frequently observed signs. VEP was abnormal in 39 workers (51%), but in 25 of those, an explanation for this finding could be found in their history and/or neurological status. In the 14 remaining cases, the connection with exposure to Hgo has been considered. A polyneuropathic pattern of EMG abnormality was found in 5 workers, an isolated EMG abnormality of the sural nerve in 13 workers. In 9 workers no other obvious cause for EMG abnormality was found but exposure to mercury. The association of EMG abnormality (especially decreased conduction velocity of the sural nerve) with VEP abnormality (especially shortening of latency) seems to be a relatively characteristic electrophysiological pattern in persons exposed to mercury vapors, suggesting an incipient, or subclinical damage to the nervous system.