The aim of this study was to identify reliable and valid subgroups of spinal pain patients, using data from the Swedish version of the Multidimensional Pain Inventory (MPI-S). A second aim was to test the generalisability of the three patient profiles described in earlier studies on the MPI ("adaptive coper", "dysfunctional" and "interpersonally distressed" patients). The study base consisted of two samples of individuals suffering from long-term, non-specific spinal pain and the results were validated across these samples. Cluster analysis was used to detect distinct groups of patients and the validity of these subgroups was evaluated on variables not used to generate the cluster solution. One subgroup was characterised by lower pain severity, lower interference with everyday activities, lower affective distress and higher life control than the other two subgroups. This patient profile was similar to the MPI adaptive coper patients. A second subgroup resembled the dysfunctional patient profile, thus displaying a worse adjustment to chronic pain than the AC patients. The third patient group reported significantly lower levels of social support from "significant others" than the other subgroups. This patient profile was similar to that of the interpersonally distressed patient group. Taken together, the results support the reliability, validity and generalisability of three subgroups of chronic pain patients derived from the MPI-S.
A valid method for classifying chronic pain patients into more homogenous groups could be useful for treatment planning, that is, which treatment is effective for which patient, and as a marker when evaluating treatment outcome. One instrument that has been used to derive subgroups of patients is the Multidimensional Pain Inventory (MPI). The primary aim of this study was to evaluate a classification method based on the Swedish version of the MPI, the MPI-S, to predict sick leave among chronic neck and back pain patients for a period of 7 years after vocational rehabilitation. As hypothesized, dysfunctional patients (DYS), according to the MPI-S, showed a higher amount of sickness absence and disability pension expressed in days than adaptive copers (AC) during the 7-years follow-up period, even when adjusting for sickness absence prior to rehabilitation (355.8days, 95% confidence interval, 71.7; 639.9). Forty percent of DYS patients and 26.7% of AC patients received disability pension during the follow-up period. However, this difference was not statistically significant. Further analyses showed that the difference between patient groups was most pronounced among patients with more than 60days of sickness absence prior to rehabilitation. Cost-effectiveness calculations indicated that the DYS patients showed an increase in production loss compared to AC patients. The present study yields support for the prognostic value of this subgroup classification method concerning long-term outcome on sick leave following this type of vocational rehabilitation.