Nerve excitability test and lead toxicity: a case-control study

Chung-Yao Chien; Jung-Der Wang; Chou-Ching Lin

doi:10.1186/s12995-023-00385-3

Nerve excitability test and lead toxicity: a case-control study

J Occup Med Toxicol. 2023 Sep 1;18(1):19. doi: 10.1186/s12995-023-00385-3.

Authors

Chung-Yao Chien¹, Jung-Der Wang^{2

3}, Chou-Ching Lin^{4

5}

Affiliations

¹ Department of Neurology, College of Medicine, National Cheng Kung University Hospital, National Cheng Kung University, 138 Sheng Li Road, Tainan, 704, Taiwan.
² Department of Public Health, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
³ Department of Occupational and Environmental Medicine, National Cheng Kung University Hospital, Tainan, Taiwan.
⁴ Department of Neurology, College of Medicine, National Cheng Kung University Hospital, National Cheng Kung University, 138 Sheng Li Road, Tainan, 704, Taiwan. cxl45@mail.ncku.edu.tw.
⁵ Department of Biomedical Engineering, National Cheng Kung University, Tainan, Taiwan. cxl45@mail.ncku.edu.tw.

Abstract

Background: Although conventional electrophysiological parameters have been proposed as clinical indicators for monitoring lead neuropathies, their correlations with blood lead level are weak. In this study, we investigated the applicability of nerve excitability tests (NETs) to evaluate lead intoxication.

Methods: Fourteen workers who were exposed to lead with an elevated blood level ranging from 17.8 to 64.9 µg/dL and 20 healthy controls with similar ages and body heights were enrolled. Both workers and controls underwent nerve conduction studies (NCSs), motor evoked potentials (MEPs) with transcranial magnetic stimulation (TMS), and NETs.

Results: NCSs showed prolonged distal latencies and decreased motor nerve conduction velocity of median nerves in the workers but without significant correlation to blood lead level (BLL). Significantly prolonged MEP latency was observed in the workers (+ 6 ms). NETs demonstrated hyperpolarized resting membrane potentials in stimulus-response curves and changes in the property of potassium channels under a hyperpolarized current in threshold electrotonus, implying that lead hyperpolarized nerves by interfering with potassium channels. NETs also showed a better correlation with BLL than conventional electrophysiological parameters.

Conclusions: Axonal hyperpolarization and central conduction delay are more apparently reflecting elevated BLL than NCS. NET may have the potential for early detection of lead neuropathy.

Keywords: Central conduction time; Inward rectifying channel; Lead intoxication; Nerve excitability test; Transcranial magnetic stimulation and motor conduction.