Cross-cultural adaptation, validation and establishment of the minimal clinically important change score of the European Portuguese core outcome measures index in patients with lumbar degenerative spine disease

Purpose The core outcome measures index (COMI) for the back is a questionnaire that evaluates five domains and has been translated into several languages and validated for different populations. We aimed to translate, cross-culturally adapt and validate it in European Portuguese for use in patients with degenerative lumbar disease. Additionally, we aimed to establish the minimal clinically important change score (MCIC). Methods The translation and cultural adaptation were done according to published guidelines. Patients awaiting surgery at a neurosurgical center completed the COMI, Oswestry Disability Index (ODI), EQ-5D questionnaires and a pain visual analog scale (VAS). To evaluate COMI’s reproducibility, patients completed the questionnaire twice within two weeks, preoperatively, in addition to answering a transition question. The MCIC was determined by analysis of postoperative changes in total COMI score, using the anchor method, with a question ascertaining surgical outcome as perceived by the patient. Results The first set of questionnaires was answered by 108 patients and the second, by 98 patients. COMI's construct validity was confirmed by demonstrating the hypothesized correlation between each domain’s score (Spearman Rho > 0.4) and the corresponding questionnaire score (ODI, EQ-5D and VAS) and through adequate correlation (Spearman > 0.6) between COMI's total score and ODI and EQ-5D total scores. Intraclass correlation coefficients between each domain and COMI’s total score were > 0.8. The MCIC was calculated as 2.1. Conclusion The cross-culturally adapted COMI questionnaire is a valid clinical assessment tool for European Portuguese-speaking patients with degenerative lumbar disease, with an MCIC of 2.1 points.