Interdisciplinary insights into tremor in dystonia: Navigating clinical controversies, definitional challenges, and pathophysiological complexities.

This review delves into the historical evolution and ongoing controversy surrounding the relationship between tremor and dystonia. The Dystonia Consensus Panel and the International Parkinson's and Movement Disorders Society's Tremor Taskforce have attempted to define these entities, but the complexity arises when patients have a combination of both dystonia and tremor. The term "dystonic tremor" has sparked diverse interpretations, with debates over its clinical features and the need for more objectively defined characteristics. Logistic regression analyses in a large cohort of dystonia patients identified determinants such as body region affected by dystonia, dystonia severity, age, and recruitment site, with unexpected associations emphasizing the subjectivity in detecting and classifying tremor. The study further discovered diverse prevalence of "dystonic tremor" based on different definitions, revealing substantial variability among investigators. The recently convened Dystonia-Tremor panel aimed to address these challenges by proposing a more uniform nomenclature, emphasizing precise and descriptive terms. Despite the complexity, instrumented measures, such as electromyography, temporal discrimination threshold, blink reflex, and trajectory shape analysis, seem to be useful in distinguishing between tremor and dystonia. The pathophysiology debate centers around the involvement of the cerebello-thalamo-cortical and basal ganglia-thalamo-cortical circuits. Evidence supports the role of both circuits in driving the pathophysiology of dystonic tremor, challenging the notion of a clear dichotomy. The review concludes by emphasizing the need for a nuanced understanding, highlighting the intricate interplay between tremor and dystonia, and the potential of instrumental measures in advancing diagnostic accuracy.
Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Aasef G. Shaikh reports financial support was provided by United States Department of Veterans Affairs. Aasef Shaikh reports a relationship with USDepartment of Veterans Affairs that includes: funding grants. Aasef Shaikh reports a relationship with American Academy of Neurology that includes: funding grants. Aasef Shaikh reports a relationship with American Parkinson's Disease Association that includes: funding grants. Aasef G. Shaikh reports a relationship with Dystonia Medical Research Foundation that includes: funding grants. Aasef Shaikh reports a relationship with CareSource that includes: funding grants. Hyder Jinnah reports a relationship with National Institutes of Health that includes: funding grants.
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