The McGill Pain Questionnaire in the assessment of phasic and tonic experimental pain: behavioral evaluation of the 'pain inhibiting pain' effect.

The McGill Pain Questionnaire (MPQ), supplemented with a German version, was administered to 10 healthy subjects to evaluate two laboratory pain models. Ischemia pain was induced as a tonic pain model and electrical intracutaneous stimuli were applied as a model of phasic pain. In addition, both pain models were employed simultaneously in order to evaluate their mutual influence. Tonic pain was rated higher than phasic pain on the affective, evaluative and miscellaneous MPQ subscales. Furthermore, the sensory descriptor choices for the two pain models were dissimilar, although the number of words chosen as well as the intensity represented by these words were of equal magnitude. These findings indicate that the sensory quality of the pain models is different and that the aversive component is much greater for the tonic pain than for the phasic pain. When applied simultaneously, tonic pain was able to inhibit phasic pain perception. This modulation could be demonstrated on visual analog scales of intensity (-44%) and aversiveness (-49%), on a 10-point category scale (-27%), and on the MPQ scores present pain intensity (PPI) (-29%), number of words chosen (NWC) (-25%) and pain rating intensity (PRI) (-28%). Differences were significant on the 5% level for the visual analog scales, the category scale and PPI. Evaluation of the MPQ subscales revealed that mainly the affective dimension of phasic pain was reduced under concurrent tonic pain. It is concluded that the MPQ is as well-suited to characterize differential analgesic effects as it is to differentiate properties of pain models.