Independent Spanish Validation of the Unified Dyskinesia Rating Scale.

The Unified Dyskinesia Rating Scale (UDysRS) assesses the severity and disability caused by dyskinesias in Parkinson's disease (PD). As part of the UDysRS development plan, the International Parkinson and Movement Disorder Society (MDS) established guidelines for official non-English translations. We present here the formal process for completing this program and the data on the first officially approved non-English version of the UDysRS (Spanish). The UDysRS translation program involves four steps: translation and back-translation; cognitive pretesting to ensure that raters and patients understand the scale and are comfortable with its content; field testing of the finalized version; and analysis of the factor structure of the tested version against the original English-language version. To be designated an official MDS translation, the confirmatory factor analysis comparative fit index (CFI) had to be ≥0.90. The Spanish UDysRS was tested in 253 native-Spanish-speaking patients with PD. For all four parts of the UDysRS, the CFI, was ≥0.94. Exploratory factor analyses of the Spanish version revealed a very clear factor structure, with three factors related to ON dyskinesia, OFF dystonia, and patient perceptions of the functional effect of dyskinesias. The Spanish version of the UDysRS successfully followed the MDS Translation Program protocol, reached the criterion to be designated as an official translation, and is now available on the MDS website for use.