The impact of psychological factors on condition-specific, generic and individualized patient reported outcomes in low back pain

BACKGROUND: An individualized patient reported outcome (PRO) has recently been recommended within LBP research, but no study has evaluated this instrument with commonly applied PROs. Moreover, the impact of psychological factors has mostly been assessed for disease-specific instruments. The objective of this study was to assess the predictive value of illness perceptions, pain catastrophizing and psychological distress on 12 month outcomes assessed by specific, generic and individualized PROs recommended in low back pain (LBP). METHODS: Secondary analysis of patients with sub-acute or chronic LBP recruited for a cluster randomized controlled trial in primary care who completed a self-administered questionnaire at baseline and 12 months. 12 month scores for the Roland Morris Disability Questionnaire (RMDQ), the EuroQol (EQ-5D), and the Patient Generated Index (PGI) were dependent variables in hierarchical regression analysis. Independent variables included baseline scores for the Brief Illness Perceptions Questionnaire (Brief IPQ), Hopkins Symptom Check List (HSCL-25), Pain Catastrophizing Scale (PCS), health/clinical and sociodemographic variables. RESULTS: Of the 216 eligible patients included, 203 patients responded to the baseline questionnaire and 150 (74%) responded at 12 months. The mean age was 38.3 (SD 10.2) years and 57.6% were female. The Brief IPQ showed a statistically significant variation in the 12-months score of all the PROs, explaining 2.5% in RMDQ, 7.9% in EQ-5D, and 3.6% in PGI. Most of the explained variation for EQ-5D scores related to illness perceptions. The PCS explained 3.7% of the RMDQ and 2.5% in the EQ-5D scores. The HSCL-25 did not make a significant contribution. CONCLUSION: Illness perceptions and pain catastrophizing were associated with 12-month outcomes as assessed by condition-specific, generic and individualized PROs. The Brief IPQ and PCS have relevance to applications in primary care that include interventions designed to enhance psychological aspects of health and where the contribution of such variables to outcomes is of interest. Further studies should assess whether the Brief IPQ perform similarly in LBP populations in other health care settings.