Spatial and gender-dependent variations in perioral pinprick sensitivity

Twenty-eight right-handed young adults participated in a sensory testing experiment to evaluate pinprick sensitivity at ten spatially matched sites on the right and left sides of the face. Stimuli were provided by a sharp-pointed dental explorer on which a rubber eraser had been positioned to minimize variations in the extent to which the skin was indented. Sharpness was defined as the magnitude at which abrupt, localized pricking/stinging sensations were evoked. A magnitude matching procedure was used to reduce among-subject variability in the data. Specifically, each estimate of sharpness was adjusted (i.e., divided) by the subject's mean estimate of the brightness of a visual stimulus. Prior to data collection, subjects were carefully instructed on the use of a common numerical scale for assignment of values of sharpness and brightness. Repeated-measures analysis of variance of the adjusted estimates of sharpness revealed a non-significant effect of gender (p > 0.4), a highly significant effect of side (p < 0.0001), and a highly significant effect of test site (p < 0.0001). Pinprick percepts were sharper on the left side of the face than on the right. Moreover, the vermilion of the upper lip exhibited the greatest sensitivity to pinprick; the vermilion of the lower lip exhibited the least sensitivity. These results suggest that use of a patient's sensitivity to pinprick during clinical neurosensory examination must be undertaken in an informed manner. A conclusion of pathological alteration in sensation can be made only after consideration of the normal spatial variations in the percept of sharpness.