Supplementary Material for: Self-Reported Dystonia and Dystonia on Neurological Examination: Prevalence and Concordance Across Time in a Prospectively Followed Essential Tremor Cohort

Introduction: Screening questions are important in identifying subgroups of individuals within a target population. Dystonic movements and postures are not uncommon in patients with essential tremor (ET). There is a gap in knowledge - no studies have assessed the validity of a self-report of dystonia in ET patients. We assessed the concordance between self-reported dystonia and the presence or absence of dystonia on examination (DOE).
Methods: We obtained self-report data from 274 ET cases in a serial study with up to five follow-up evaluations. At each assessment, participants could self-report dystonia, and they underwent a detailed neurological examination, from which a movement disorders neurologist assessed for the presence of DOE.
Results: Across time, the prevalence of self-reported dystonia and DOE ranged from 0.0% - 4.3% and 8.6% -17.5%, respectively. There were 74 cases with either self-reported dystonia or DOE; in only 3 (4.1%) was there a positive concordance between the two at each of their evaluations. Values for sensitivity ranged from 0.0% - 40%; specificity from 96.1% - 100%; positive predictive value from 0.0% - 67.0% (median 30.0%); and negative predictive value, from 83.1% - 94.4%.
Conclusion: Our study provides important insights into the validity of self-report data on dystonia in ET and the prevalence of DOE in ET. Our findings suggest that self-reported dystonia was not a valid means to identify DOE in ET.