Dystonia is a rare disorder characterized mostly by involuntary slow and twisting movements. On the other hand, tremor is a common disorder characterized by regular shaking movements. Patients with dystonia are often misdiagnosed with tremor. Patients with tremor are often misdiagnosed with dystonia. The result is that these patients may be treated with the wrong types of medications, sometimes for years. In addition, previous small studies coming from single sites have indicated that these two disorders are often combined. However, estimates of the frequency of their combination vary considerably.
The objective of this study was to define the frequency of co-occurring dystonia with tremor, and the factors that influence this combination. Our multicenter study involved 2,362 subjects with dystonia recruited by 37 Dystonia Coalition sites distributed across North America, Europe, and Australia. Movement disorder experts used a standardized exam to record dystonia and tremor.
In the whole group, 53 percent of subjects with dystonia also had tremor. However, this percentage depended on several factors, including the type of dystonia, the duration of dystonia, and the severity of dystonia.
We were surprised that site of recruitment had a significant impact on the frequency of tremor in these dystonia cases. This impact is probably not related to geographical location of the subjects, but rather to differences in how investigators diagnose dystonia or tremor.
These findings help us understand the clinical heterogeneity in individuals with dystonia. They also point towards the need for more stringent diagnostic criteria, so that more consistent results can be obtained across the world. We hope that better information regarding their combination will raise awareness that both need to be considered, as well as aiding faster recognition of both disorders.
Overall, our study points to an important relationship between two distinct disorders. Understanding the biological basis for this connection is important for both disorders—findings in dystonia may provide useful insights into tremor, and vice versa.
The Dystonia Coalition (DC) is part of the Rare Diseases Clinical Research Network (RDCRN), which is funded by the National Institutes of Health (NIH) and led by the National Center for Advancing Translational Sciences (NCATS) through its Office of Rare Diseases Research (ORDR). DC is funded under grant number U54NS116025 as a collaboration between NCATS and the National Institute of Neurological Disorders and Stroke (NINDS).