Objective: To evaluate the validity and reliability of recordings of pain location among patients with pain from 2 different sources, using the McGill Pain Map (MPM).
Methods: Consecutive outpatients from a rheumatology clinic and inpatients recovering from surgical interventions participated in a structured interview during which the McGill Pain Questionnaire and the MPM were administered. After an interval of 3 to 6 weeks for the rheumatology patients and 1 to 2 days for the postoperative patients, a 2nd identical interview was administered. Criterion related validity was examined by testing whether the extent [total number of painful areas (NPA)] and distribution (individual body areas affected) of pain differed significantly between the 2 patient groups and whether, among postoperative patients, the distribution of pain was consistent with the site of surgical incision. Test-retest reliability of the recordings on the MPM was measured by calculating a kappa coefficient for each individual body area on the MPM, and an intraclass correlation coefficient for the NPA.
Results: 51 rheumatology and 47 postoperative patients were interviewed. Significant differences in the total NPA (4.1 +/- 3.0 vs 11.5 +/- 6.2; p < 0.001) and in the distribution of the painful areas were observed between the 2 groups. Among postoperative patients, there was no significant difference in the NPA between the 2 interviews (4.1 +/- 3.0 vs 4.3 +/- 3.5; p = 0.53), while among rheumatology patients, there was a reduction in the NPA at the second interview (11.5 +/- 6.2 vs 9.8 +/- 5.3; p = 0.007). Reliability of the recordings of pain location by individual areas averaged 0.50 (range 0.04 to 0.76). The reliability of the NPA was 0.82 for the combined group of patients (0.71 and 0.84, respectively).
Conclusion: Recordings of pain location using the MPM are valid and reliable. The MPM is a valuable instrument for studies of the distribution of pain in populations.