Minimal clinically important difference for the historic parts of the Unified Dyskinesia Rating Scale

Background: Motor complications represent an important clinical problem in the treatment of Parkinson's disease (PD). The Motor Complications Part of the Movement Disorder Society-sponsored Unified Parkinson's Disease Rating Scale (MDS-UPDRS Part IV) and the Unified Dyskinesia Rating Scale (UDysRS) are among the most reliable instruments to evaluate these problems. The minimal clinically important difference thresholds are the smallest changes in the outcome measures that are clinically meaningful.

Aims: The aim of our study was to calculate the minimal clinically important difference thresholds for the MDS-UPDRS Part IV and the historic parts of the UDysRS.

Methods: A total of 1044 paired investigations of 436 patients were analyzed. Changes in the respective outcome measures (MDS-UPDRS Part IV, UDysRS Parts I and II) were compared to the Patient-rated Global Impression of Improvement scores (anchors). Subsequently, we applied receiver-operating characteristic analysis to ascertain the MCID thresholds with optimal sensitivity and specificity.

Results: Any improvement greater than 2.1 points or any worsening greater than 1.8 points on UDysRS Part I represents a minimal, yet clinically meaningful change. In reference to UDysRS Part II, the smallest changes considered clinically relevant are 1.8 and 1.7 points for improvement and deterioration, respectively. The thresholds for the MDS-UPDRS Part IV are 0.9 points for improvement and 0.8 points for worsening.

Conclusions: Our estimates may allow the judgment of the clinical relevance of numeric changes in the dyskinesia scales.