Reply: “Segmental vs. Multifocal: The 2025 Dystonia Classification Is Helpful”

Thank you for your interest in our article on similarities and differences between segmental and multifocal isolated dystonias.1 Several points raised in the letter may reflect misinterpretations of the study's aims, methods, and conclusions.2 Our work examined whether idiopathic adult-onset isolated dystonia (IAOD) cases classified as “segmental” versus “multifocal” in two large registries can be distinguished by features other than contiguity.1 Specifically, we sought empirical justification for these traditional subgroups. We found that most differences disappear after adjustment for site of onset, suggesting that the segmental/multifocal distinction may have limited independent clinical value. This observation supports the view that current groups based on body distribution of dystonia are intrinsically unstable rather than clinically informative. Body regions were defined according to the anatomical regions of the Global Dystonia Rating Scale and classified as segmental or multifocal according to standard practices at the time of data collection. These data were collected long before publication of the 2025 consensus, which provided new recommendations for defining these distributions.3 Reorganizing legacy registry data into the 2025 framework is neither feasible nor appropriate because it would require post hoc assumptions about what was examined historically and how recorded observations map onto newly defined regions, potentially introducing artifactual classifications. Our approach prioritized transparency and reproducibility within the datasets' original operational definitions. Contrary to what was asserted, oromandibular dystonia was analyzed and reported, and proximal limb regions were not excluded. Proximal and distal limb involvement were considered together as dystonia of the corresponding limb, consistent with common clinical practice, the registries' operational structure, and recent data showing a high correlation between dystonia scores in upper and lower regions of a limb.4 This strategy does not inflate the prevalence of multifocal dystonia; rather, it reduces misclassification, given that proximal limb involvement in IAOD is rare and proximal postures are frequently compensatory and not always reliably distinguishable from true dystonia. The suggestion that our findings are driven by an artifactual limb subdivision is, therefore, unsupported by our analyses. Finally, the comparison between the 9.6% rate of near-simultaneous onset reported in a recent study5 and the 31% to 52% figures in our work1 reflects different denominators. The 9.6% figure refers to near-simultaneous onset calculated across the entire IAOD population, including focal, segmental, and multifocal cases.5 In contrast, the 31% to 52% figures represent the proportion of segmental or multifocal onset within the subgroup of patients who ultimately had segmental or multifocal dystonia and were analyzed.1 These measures are, therefore, not comparable. In any case, our conclusions do not depend on fine-grained reconstruction of onset timing but on replicated comparative patterns across two independent registries with adjustment for site of onset. We support the prospective adoption of the 2025 classification framework.3 Our study does not undermine this effort; rather, it clarifies how traditional distribution-based categories behave in legacy datasets and why the clinical value of some groupings is likely limited. Indeed, the 2025 classification questioned the value of distinguishing segmental from multifocal data. Our observations provide evidence that this distinction may indeed be unnecessary. (1) Research project: A. Conception, B. Organization, C. Execution; (2) Statistical Analysis: A. Design, B. Execution, C. Review and Critique; (3) Manuscript: A. Writing of the first draft, B. Review and Critique. H.A.J.: 1A, 1B, 1C, 3A, 3B. V.V.: 1A, 1B, 1C, 3A, 3B. G.D.: 1A, 1B, 1C, 3A, 3B. The authors have nothing to report. Ethical Compliance Statement: The authors confirm that the approval of an institutional review board was not required for this work. Informed patient consent was not necessary for this work. We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines. Funding Sources and Conflict of Interest: No specific funding was received for this work. The authors declare that there are no conflicts of interest relevant to this work. Author disclosures are available in the Supporting Information. Data sharing not applicable to this article as no datasets were generated or analyzed during the current study. Data S1. Supplementary Information. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.