Preface to the Fifth <scp>MDS</scp> Video Challenge Case Supplement for <i>Movement Disorders Clinical Practice</i>

The MDS Video Challenge is an annual and traditional event at the International Congress of Parkinson's Disease and Movement Disorders. This session has been the major attraction of the annual conference among the participants, especially the residents, fellows, and young faculty members. This special issue documents the cases presented at the 2023 MDS Video Challenge in Copenhagen, Denmark, along with the respective videos and discussions with key learning points. These cases were shortlisted from 168 submissions (83 from the Asian and Oceanian sections, 38 from the European section, 39 from the Pan-American section, and 8 from the African section) highlighting challenging phenomenological and etiological associations. The number of cases submitted was twice compared to last year, highlighting the growing interest of the participants in all regions. The masters of ceremonies for 2023 were Drs. Anthony E. Lang (Canada) and Kailash P. Bhatia (United Kingdom), and the panel of discussants comprised Drs. Norbert Brueggemann (Germany), Veronica Bruno (Canada), Hrishikesh Kumar (India), Matej Skorvanek (Slovakia), and Aparna Wagle Shukla (United States). This special issue includes 8 submissions, from 7 different countries, namely Canada, Chile, France, India, Italy, Malaysia, and the Netherlands. All the information from these educational cases has been thoroughly synthesized by the authors for publication in the supplement.1-8 Thus, it allows everyone to review and learn from them anytime. There is a wide diversity in clinical presentation and final diagnosis; however, cases related to genetic disorders (5 cases) and underlying autoimmune conditions (2 cases) are the major highlights. This trend is consistent with the recent editions of the supplements published in the past 4 years.9-12 The presented genetic cases have raised interesting key points, namely the many faces of genes such as ATP1A3, including atypical phenotypes1; the possibility that a well-established family history may not always be present; and the presentation in populations where they have been rarely observed.3 Another aspect was that sometimes typical magnetic resonance imaging findings for a disorder might not be specific, and other related disorders should be considered.4 The 2 cases on autoimmune etiology remind us that, when suspecting an autoimmune neurological disorder, the same phenotype can be associated with multiple antibodies. Conversely, 1 antibody can present with different phenotypes or a combination of a full range of symptoms.7, 8 Additional important take-home messages are the importance of a levodopa trial in patients with dystonia, as it might be beneficial,5 and the recognition of parkinsonism after an uncal herniation.6 Finally, we should be cautious before suggesting a functional overlay and keep in mind the uncommon association of deafness with dystonia.2 Cases presented during the MDS Video Challenge are complex with different phenomenology and etiology. However, they help the audience in learning pattern recognition and approach to these disorders. They enrich our clinical knowledge and skills helping in our therapeutic decision-making. As the editors of this supplement, we are grateful to the presenters, masters of the ceremonies, patients, and their family members, but also to the journal reviewers of all submitted case reports. We look forward to future editions of the MDS Video Challenge. (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. S.P.: 1A, 1B, 1C, 2A, 2B, 2C, 3A, 3B C.G.-S.: 1A, 1B, 1C, 2A, 2B, 2C, 3A, 3B Ethical Compliance Statement: We confirm that the approval of an institutional review board was not required for this work. We also 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 Conflicts of Interest: No specific funding was received for this work. The authors declare that there are no conflicts of interest relevant to this work. Financial Disclosures for the Previous 12 Months: C.G.-S. received speaker honoraria from Insightec and Asociación Madrileña de Neurología. She received travel expenses to attend scientific conferences from Boston Scientific and Esteve. The authors declare that there are no additional disclosures to report.

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