Verbal instructions influence pain thresholds assessment: A study using manual and electronic mechanical stimulators.

BACKGROUND

Quantitative sensory testing (QST) relies on psychophysical techniques and instructions to test subjects. This study examined the effect of different verbal instructions for mechanical pain thresholds (MPTs) using two different stimulation techniques; weighted pinprick stimulators and an electronic von Frey device (EvF). The test-retest reliability and within session variability in the MPTs for each verbal instruction were compared in addition.

METHODS

Sixteen healthy volunteers participated. The MPTs with two different verbal instructions (pinprick and pain) were evaluated with two different stimulation techniques at three test sites: on the skin of the right cheek (face), on the buccal gingival mucosa of the right upper premolar region (gingiva) and on the tip of the tongue (tongue). The exact same protocol was repeated 1-2 weeks later for test-retest reliability.

RESULTS

The MPT values with pain instruction were significantly higher than the values with the pinprick instruction for all sites and both stimulation techniques (p < .001). The absolute values of MPT were affected by instruction differences but it did not seem to have a major impact on reliability, and there were no significant differences in within session variability (p > .079) between the two different verbal instructions (pinprick and pain).

CONCLUSIONS

The specific wording of standardized QST instructions resulted in significant differences in MPT values regardless of which of the two stimulation techniques were used; pinprick stimulators or EvF. This emphasizes the importance of careful standardization of QST instructions in addition to standardization of the stimulus application.

SIGNIFICANCE

Quantitative sensory testing (QST) is a widely accepted tool for somatosensory testing and the reliability and variability in the QST test battery has been found to be acceptable. Changing minor details in the wording of standardized QST verbal instructions resulted in significant differences in mechanical pain thresholds. This emphasizes the importance of careful standardization of QST instructions in addition to standardization of the stimulus application.