Content overlap of 91 dystonia symptoms among the seven most commonly used cervical dystonia scales

Introduction Dystonia is a movement disorder characterized by sustained or intermittent muscle contractions. Cervical dystonia (CD) is the most common focal dystonia. There are several instruments assessing the symptoms of CD. However, different scales assess different features which may lead to poor patient evaluation. Aim The aim of the study was to evaluate the degree of overlap of most often used CD rating scales identified by the literature review. Methods A thorough search of the Medline database was conducted in September 2021. Then the frequency of each scale was calculated, and 7 most common scales were included in the content overlap analysis using Jaccard index (0 – no overlap, 1 – full overlap). Results Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS), Tsui score, Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS), Cervical Dystonia Impact Profile 58 (CDIP-58), Craniocervical Dystonia Questionnaire 24 (CDQ-24), Cervical Dystonia Severity Rating Scale (CDSS), Cervical Dystonia Severity Rating Scale (DDS) and The Dystonia Non-Motor Symptoms Questionnaire (DNMSQuest) were the most common scales. 91 CD symptoms were distinguished from 134 items used in the scales. The mean overlap among all scales was 0.17. 52 (62%) symptoms were examined by more than one scale. The CIDP-58 captured the highest number of symptoms (63.0%), while the CDSS captured the lowest number (8.0%). None of the symptoms were examined by seven instruments. Conclusions There was a very weak overlap among scales. High inconsistency between the scales may lead to highly different dystonia severity assessment in clinical practice. Thus, the instruments should be combined.