Vibrotactile threshold and
pin-prick sensitivity as indicators of subclinical changes
in somatosensory function: effects of environmental exposure
to arsenic in drinking water
DA Otto1, HK Hudnell1, Y-H
Li2, YJ Xia2
1US Environmental Protection Agency, Research Triangle Park,
NC 27711 USA
2Institute of Endemic Disease, Huhhot, Inner Mongolia
Introduction.
Peripheral neuropathy results from exposure to a variety of
neurotoxic compounds. Clinical assessment of peripheral
neuropathy is commonly based on electrophysio-logical
measures of nerve conduction velocity (NCV). However, data
on early, subclinical changes in neurologic function
resulting from exposure to neurotoxicants are needed for
human health risk assessment. Behavioral measures of
vibrotactile thresholds (VTT) and pin-prick sensitivity
(PPS) provide non-invasive methods for assessing
somatosensory function that are suitable for use in field
studies. VTT measures have previously identified subclinical
effects from exposure to organic solvents, jet fuel,
elemental mercury and organophosphate pesticides (1). The
current study investigated the effects of environmental
exposure to arsenic in drinking water on somatosensory
function using VTT and PPS techniques.
Methods.
A population of farm families living in the Bamen region of
Inner Mongolia chronically exposed to arsenic in well water
were screened for potentially confounding factors. 309
residents (mean age 35.8 +/- 12.8 years) qualified for
participation. Subjects were assigned to three exposure
groups based on arsenic levels in individual wells as
follows: low (<20 ug/L; N=97), medium (100-300 ug/L; N=109)
and high (400-700 ug/L; N=103). VTT was measured on the
dorsal surface of digit 2 and the ventral surface of digit 5
on each hand. PPS was assessed on both arms and both legs.
Results.
VTT was significantly elevated and PPS was significantly
reduced in the high exposure group relative to both the
medium and low exposure groups. The data suggested a larger
exposure effect on PPS than VTT.
Conclusion.
These results indicate that subclinical effects of chronic
arsenic exposure on somatosensory function are observable
only at exposure levels well above those associated with
increased risk for cancer. Differences between the VTT and
PSS results suggest that small diameter unmyelinated axons
with free nerve endings in superficial skin layers may be
more susceptible to exposure than the larger diameter and
myelinated axons with Pacinian corpuscle receptors located
in deeper skin layers. This is an abstract of a proposed
presentation and does not necessarily reflect EPA policy.
(1) D Mergler. Behavioral
Neurophysiology: Quantitative Measures of Sensory Toxicity.
In: LW Chang & W Slikker (eds). Neurotoxicology: Approaches
and Methods, New York, Academic Press, 1995, ch47 pp727-736.