The Minimal Clinically Important Difference of the Carpal Tunnel Syndrome Symptom Severity Scale

Clinical research in hand surgery has embraced the use of outcomes questionnaires to serve as an important end point of patient outcomes. Although other outcomes parameters such as grip strength, pinch strength, and range of motion often are presented, the ability of patient-rated outcomes questionnaires to capture important changes in patients’ health-related quality of life is considered a more relevant outcome. The interpretation of changes in outcomes scores, however, can be challenging. Most researchers present an effect size or a standardized response mean to estimate changes in outcomes. Both rely on the amount of change based on the standard deviation to estimate the effect size. By using research from the social sciences, in which questionnaire scores often are used, Cohen defined an effect size of 0.2 as small, 0.5 as medium, and more than 0.8 as large. Other researchers may report the statistical difference, which in many cases may not be important clinically and the effect may be difficult to interpret. For example, a 1-kg change in grip strength is easy for most people to relate to and can be considered a clinically significant change. But a 0.1-kg difference in a study with a large sample size can be significant statistically but may not be significant clinically. Investigators and physicians may interpret a 10-point difference in the activities of daily living score on the Michigan Hand Outcomes Questionnaire differently. Does this 10-point difference (range, 0–100) indicate a greater ability to turn a doorknob or to dress? Similarly does a 1-point change (scale, 0–5) in the carpal tunnel questionnaire show a clinically significant improvement? It remains a challenge in outcomes research to determine whether a clinically important difference has been reached for different outcomes questionnaires across different conditions. Because most clinical studies in hand surgery use outcomes questionnaires, it is important for the readers of the Journal to be able to interpret outcomes questionnaire data. The minimal clinically important difference (MCID) is useful in “judging the magnitude of the benefit when comparing two treatments, calculating a sample size, making inferences about the percentage of patients improved by a therapeutic intervention, and making cost effectiveness comparisons.” But how does a clinician define what constitutes an MCID? In addition, whose frame of reference should be used in defining the MCID? For example, an employer may define an MCID as a change that will allow patients to return to work. A patient may define an MCID as the ability for self-care. A hand surgeon may define an MCID as improvement sufficient for the patient not to return to the clinic for further treatment. Therefore the fluidity of the MCID concept relies on the perspectives of the evaluator and the study participants. Individual differences in the assessment of changes create variability in establishing the MCID and remain a difficult concept in outcomes research. The article by Ozyurekoglu et al, in this issue of the Journal, emphasized the issue of a clinically important difference. By using the so-called heuristic technique, the authors explored the concept of MCID. Although some researchers may question the relevance of calculating the MCID for steroid injection in carpal tunnel syndrome, this article increased the awareness of MCID to expand the understanding of how to interpret outcomes research in hand surgery.