Impact of skin temperature on the screening electromyography results within the occupational medical examinations

Česká verze

Authors: A. Šplíchalová; H. Tomášková; K. Hrnčíř; L. Martinková; O. Jašurková; N. Ambrúžová
Authors place of work: Zdravotní ústav se sídlem v Ostravě ředitel RNDr. Petr Hapala
Published in the journal: Pracov. Lék., 68, 2016, No. 1-2, s. 47-53.
Category: Původní práce

*Předneseno na XXXII. kongresu pracovního lékařství, Jihlava, 15.–16. 10. 2015.

Summary

The result of an electromyography (EMG) test may be influenced by many factors. A fundamental effect on nerve impulse conduction has a skin temperature. Its reduction leads to a reduced conduction velocity and distal latency prolongation. Therefore the methodology recommends the skin temperature between 32–36 °C and below this value the examination cannot be considered valid. In case of insufficient skin temperature, the patients’ limbs are necessary to be heat up first. If heat up is not possible an emergency solution is applied by the correction of observed distal latency values of 0.3 ms or of 0.1 ms for every degree under the standard temperature. The aim of this study was to compare the measurement results of the distal motor latency (DML) of median nerves at the lack of skin temperature and after heating hands at standard temperature. The further goal was to verify the reliability of the DML measurement results after applying the above corrections during the screening EMG within occupational medicine examinations.

DML measurement of median nerves in wrist area was realized by the EMG TruTrace 2 device, which also includes a device for continuous measurement of skin temperature. In total 40 persons were examined – first at room temperature, when the skin temperature of hands did not reached 32 °C, and retested after heating hands up to the standard temperature 33–36 °C. DML values were compared by a paired t-test and evaluated on the 5% level of significance. The data analysis was conducted using the software STATA v.13.

In comparison with the DML results after heating up to the standard temperature the DML values at room temperature were significantly prolonged (p < 0.001) that led to false positive results in 55 % of the findings. Conversely, if correction 0.3 ms/1 °C was applied the resulting DML values significantly decreased (p < 0.001) and thus led to false negative results. Neither the correction 0.1 ms/1 °C has not been confirmed, as reliable especially in persons with borderline, and abnormal findings, whose results showed statistically significant differences (p < 0.05).

In conclusion, it can be summarized that a lack of compliance with the standard skin temperature during the DML testing poses a significant risk of false positive findings. The study results did not confirm the reliability of the corrections which use in practice may be a significant source of errors, especially in the case of abnormal or borderline findings. Although the abnormal findings of the EMG screening are verified by a neurologist examination, the standard methodology including recommended skin temperature is necessary to be respected during the screening test. Compliance with those conditions lead to a minimization of errors in tests and interpreting the results.

Keywords:
skin temperature – distal motor latency – median nerve – screening electromyography – occupational medical examinations

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