Differentiating sensory and affective-sensory pain descriptions in patients undergoing magnetic resonance imaging for persistent low back pain.

The study design is a cross-sectional survey with psychometric analysis. The objective is to determine the validity of a modified version of the Short-Form McGill Pain Questionnaire (SF-MPQ). The SF-MPQ has been widely used to differentiate between reports of sensory and affective pain. The validity of this instrument to reflect independence between these constructs remains unclear. The SF-MPQ, the Roland-Morris Questionnaire (RM) and a measure of current pain intensity were completed by 373 patients undergoing lumbar magnetic resonance imaging (MRI). Four hypothesized factor structures for the SF-MPQ (three 2-factor and one 1-factor solution) were tested using confirmatory factor analysis. A modified 2-factor solution (MSF-MPQ) containing 3 items labeled sensory and 5 items labeled affective-sensory had the best degree of fit. Correlations between factors were substantially lower for the modified 2-factor solution (0.48) than for previously described 2-factor solutions (0.88 and 0.92) indicating a higher degree of independence between these factors. Correlations with measures of pain intensity and the RM were significant, but slightly lower, for the subscales of the modified 2-factor solution (0.26-0.40) than for the subscales of the previously described 2-factor solutions (0.34-0.45). The MSF-MPQ can be used as a brief tool to differentiate the language used to describe pain in patients who are undergoing lumbar MRI. The evidence indicates that this clinical tool can be used to categorize how these patients describe their pain and potentially may be very valuable in determining the optimal course of treatment.