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This letter raises several important issues about the measurement of current perception threshold (CPT) and its application to the assessment of HAVS patients which the authors felt were related to the interpretation of our research.Our study highlighted the high prevalence of proximal neuropathy at the wrist in HAVS patients and the importance of the measurement of this neurological outcome. In a clinical diagnostic setting, the most definitive test for this proximal neuropathy is a nerve conduction study (NCS), which includes measurement of motor and sensory conduction velocities, latencies and amplitudes [1,2]. The CPT testing, however, is not without utility. In particular, we were intrigued by the fact that the CPT measurements in our study were more predictive than the NCS measurements of sensory abnormalities in the hand. In fact, the highest odds ratios for Stage 2 or greater of the Stockholm Neurological Scale were obtained for the CPT measurements. These results suggest the possibility of a second type of more distal neurological lesion in the fingers in addition to the proximal neuropathy in HAVS patients.
However, these results need to be corroborated by additional studies. Future research should focus on the relation between vibration exposure and neuroselective CPT outcomes, especially after controlling for proximal neurological effects, which may also affect CPT measurement in the fingers. Also, it would be very useful to determine if the neuroselective CPT abnormalities reported in animal studies could be clearly demonstrated in HAVS patients. Such findings would support the presence of both proximal and distal lesions in HAVS patients and help to justify utilization of quantitative sensory tests such as CPT in addition to NCS in the assessment of neurological effects in vibration-exposed workers.
Department of Occupational and Environmental Health, St. Michael's Hospital, 30 Bond Street, Toronto, Ontario, Canada M5B 1W8
Department of Public Health Sciences, University of Toronto, Toronto, Ontario, Canada
Department of Environmental Health, Harvard School of Public Health, Boston, MA, USA Department of Epidemiology, University of Nebraska Medical Center, Omaha, NE, USA
e-mail: houser{at}smh.toronto.on.ca
e-mail: ilander{at}hsph.harvard.edu
References
- Midroni G. Electromyography: indications and limitations. Can J Diagn (1996) 129–138.
- Shy ME, Frohman EM, So YT, et al. Quantitative sensory testing: report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology. Neurology (2003) 60:898–904.
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