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Cohort study.To estimate the minimal clinically important change (MCIC) on the pain intensity numerical rating scale (PI-NRS) and the Roland Morris Disability Questionnaire (RMQ) in subacute and chronic patients with low back pain (LBP), with and without referred pain to the leg (LP), seen in the routine clinical practice of the Spanish National Health Service.MCIC have been explored in Anglo-Saxon and Northern European LBP patients. No data on the influence of LP on MCIC are available. In Southern European patients, determinants of disability have shown to be different, and MCIC for pain and disability are unknown.Data from the postmarketing surveillance of 1349 LBP subacute and chronic patients treated in routine clinical practice were used for this study. Three different methods were used to estimate the MCIC over a 12-week period: the mean change score (MCS), the minimal detectable change (MDC), and the optimal cutoff point in receiver operant curves (OCP). Patients' own “global perceived effect” was used as the external criterion. The effect on MCIC of initial scores, duration of pain, and existence of LP were assessed.Different methods led to different MCIC values, with those deriving from OCP being the smallest. Depending on the methods which were used, the MCIC for LBP ranged from 1.5 to 3.2 PI-NRS points in patients with a baseline score below 7 points, and from 2.5 to 4.3 in patients with a baseline score ≥9 points. The MCIC for disability ranged from 2.5 to 6.8 RMQ points in those with baseline scores below 10 points, and from 5.5 to 13.8 inthose baseline scores ≥15 points. These values were similar for patients with LP, and were not influenced by the duration of pain.In subacute and chronic patients, improvements in LBP of ≤1.5 PI-NRS points, or in disability of ≤2.5 RMQ points should be seen as irrelevant. In those patients, MCIC range values are similar in patients with LP, are consistent across different cultural settings and remain stable no matter what the duration of pain is.