Which neurophysiologic findings are characteristic of mercury-related toxic neuropathy?

Updated: Dec 06, 2017
  • Author: Jonathan S Rutchik, MD, MPH, FACOEM; Chief Editor: Tarakad S Ramachandran, MBBS, MBA, MPH, FAAN, FACP, FAHA, FRCP, FRCPC, FRS, LRCP, MRCP, MRCS  more...
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Answer

Neurophysiologic abnormalities associated with mercury exposure (inorganic and organic)

  • Inorganic mercury is noted to produce a sensory or sensorimotor polyneuropathy similar to that produced by arsenic. Chloralkali plant workers (n=138) with long-term inorganic mercury vapor exposure were noted to have elevated urine mercury levels and reduced sensation on quantitative testing, prolonged distal latencies with reduced sensory-evoked response amplitudes, and increased likelihood of abnormal needle EMG findings. Factory workers exposed to elemental mercury vapor with elevated urine mercury concentrations had prolonged motor and sensory ulnar distal latencies. Slowing of the median motor NCV was found to correlate with both increased levels of mercury in blood and urine and with increased numbers of neurological symptoms. Sensory deficits found with short-term exposure to mercury vapor, whereas motor nerve impairment occurred with longer periods of exposure.

  • Chloralkali workers exposed to inorganic mercury vapors for an average of 12.3 years were found to have median motor and sensory NCVs that were slightly reduced among the highly exposed subjects. Seventeen thermometer factory workers had high urine and blood mercury levels but no symptoms; 88% had subclinical neuropathy, mainly distal and axonal neuropathy. In another study, a sensory polyneuropathy was found in 11% of workers exposed to inorganic mercury, while a sensorimotor polyneuropathy was found in 27% of workers.

  • Chloralkali workers who were exposed to inorganic mercury for an average of 7.9 years and had ceased working in that environment an average of 12.3 years prior to the study were found to have both median sensory NCV and amplitude of the sural nerve associated with measures of cumulative exposure to mercury. A study reviewing the relationship between exposure-related indices and neurological and neurophysiological effects in workers previously exposed to mercury vapor revealed that, of 298 dentists with long-term exposure to mercury amalgam vapor evaluated for peripheral neuropathy, 30% had polyneuropathies. Another paper reported that one dentist apparently had an unelicitable sensory superficial peroneal nerve action potential that returned to normal following penicillamine treatment.

  • Industrial workers with long-term exposure to mercury were found to have performance decrements in neuromuscular functions that were reversible and correlated with blood and urine mercury levels.


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