Responsiveness and minimal clinically important difference for pain and disability instruments in low back pain patients

BACKGROUND: The choice of an evaluative instrument has been hampered by the lack of head-to-head comparisons of responsiveness and the minimal clinically important difference (MCID) in subpopulations of low back pain (LBP). The objective of this study was to concurrently compare responsiveness and MCID for commonly used pain scales and functional instruments in four subpopulations of LBP patients. METHODS: The Danish versions of the Oswestry Disability Index (ODI), the 23-item Roland Morris Disability Questionnaire (RMQ), the physical function and bodily pain subscales of the SF36, the Low Back Pain Rating Scale (LBPRS) and a numerical rating scale for pain (0–10) were completed by 191 patients from the primary and secondary sectors of the Danish health care system. Clinical change was estimated using a 7-point transition question and a numeric rating scale for importance. Responsiveness was operationalised using standardardised response mean (SRM), area under the receiver operating characteristic curve (ROC), and cut-point analysis. Subpopulation analyses were carried out on primary and secondary sector patients with LBP only or leg pain +/- LBP. RESULTS: RMQ was the most responsive instrument in primary and secondary sector patients with LBP only (SRM = 0.5–1.4; ROC = 0.75–0.94) whereas ODI and RMQ showed almost similar responsiveness in primary and secondary sector patients with leg pain (ODI: SRM = 0.4–0.9; ROC = 0.76–0.89; RMQ: SRM = 0.3–0.9; ROC = 0.72–0.88). In improved patients, the RMQ was more responsive in primary and secondary sector patients and LBP only patients (SRM = 1.3–1.7) while the RMQ and ODI were equally responsive in leg pain patients (SRM = 1.3 and 1.2 respectively). All pain measures demonstrated almost equal responsiveness. The MCID increased with increasing baseline score in primary sector and LBP only patients but was only marginally affected by patient entry point and pain location. The MCID of the percentage change score remained constant for the ODI (51%) and RMQ (38%) specifically and differed in the subpopulations. CONCLUSION: RMQ is suitable for measuring change in LBP only patients and both ODI and RMQ are suitable for leg pain patients irrespectively of patient entry point. The MCID is baseline score dependent but only in certain subpopulations. Relative change measured using the ODI and RMQ was not affected by baseline score when patients quantified an important improvement

What is an acceptable outcome of treatment before it begins? Methodological considerations and implications for patients with chronic low back pain

Understanding changes in patient-reported outcomes is indispensable for interpretation of results from clinical studies. As a consequence the term “minimal clinically important difference” (MCID) was coined in the late 1980s to ease classification of patients into improved, not changed or deteriorated. Several methodological categories have been developed determining the MCID, however, all are subject to weaknesses or biases reducing the validity of the reported MCID. The objective of this study was to determine the reproducibility and validity of a novel method for estimating low back pain (LBP) patients’ view of an acceptable change (MCIDpre) before treatment begins. One-hundred and forty-seven patients with chronic LBP were recruited from an out-patient hospital back pain unit and followed over an 8-week period. Original and modified versions of the Oswestry disability index (ODI), Bournemouth questionnaire (BQ) and numeric pain rating scale (NRSpain) were filled in at baseline. The modified questionnaires determined what the patient considered an acceptable post-treatment outcome which allowed us to calculate the MCIDpre. Concurrent comparisons between the MCIDpre, instrument measurement error and a retrospective approach of establishing the minimal clinically important difference (MCIDpost) were made. The results showed the prospective acceptable outcome method scores to have acceptable reproducibility outside measurement error. MCIDpre was 4.5 larger for the ODI and 1.5 times larger for BQ and NRSpain compared to the MCIDpost. Furthermore, MCIDpre and patients post-treatment acceptable change was almost equal for the NRSpain but not for the ODI and BQ. In conclusion, chronic LBP patients have a reasonably realistic idea of an acceptable change in pain, but probably an overly optimistic view of changes in functional and psychological/affective domains before treatment begins