The MDS-UPDRS was introduced in Movement Disorders in 2008 and has increasingly been used in the evaluation of PD patients. 1 The clinimetric program to establish its factor structure was anchored in an assessment of over 800 subjects. After the success of this program, the Movement Disorder Society (MDS) has encouraged official translations into non-English languages.
In the process of the non-English translation program, the analytic team reran our factor analysis of the English language and found a discrepancy between our original and replication analyses for dopamine dysregulation syndrome (DDS). In the original factor structure report, DDS had an item loading of 0.49 on factor 1 of part I. In the rerunning of the analysis for the current program, however, the same item had an item factor loading of only 0.19, falling outside the acceptable range to be identified with any factor in the scale. The DDS item was the only one that did not replicate in our reanalysis of the original data.
Given that DDS is a highlighted area of research and clinical care, we alert readers of the journal to our reporting error. The low factor loading indicates that this item does not capture information that relates to any other element of PD in the rest of the MDS-UPDRS. It is possible that impulse control disorder behaviors being assessed in this item do not relate to other aspects of the overall disease and its treatment, but studies have documented comorbid behaviors, including cognitive dysfunction, that we would have expected to cluster statistically with this item. 2 Alternatively, the item itself may not be created well and, therefore, is not capturing accurate information on the target behavior.
The MDS has a program to review available scales for assessing PD, and a critique of scales to document and rate the severity of impulse control disorders is currently in development. We regret having reported an inaccurate statistic and have already informed the chair of this task force. We will use our revised analysis as we evaluate the non-English translations of the MDS-UPDRS.