Phenotypic Features of Isolated Essential Tremor, Essential Tremor Plus, and Essential Tremor-Parkinson’s Disease in a Movement Disorders Clinic

Abstract

Background: Patients with essential tremor were initially considered to have isolated tremor, but additional motor and non-motor features have been increasingly recognized. The term "essential tremor plus" was adopted by the Task Force on Tremor of the International Parkinson and Movement Disorder Society to describe essential tremor patients with additional neurologic signs.Objectives: To characterize essential tremor patients and their phenotypes in a movement disorders clinic population in the context of the new tremor classification.Methods: Demographic, clinical, historical, treatment, and diagnostic data were retrospectively collected on 300 patients diagnosed by movement disorder experts with essential tremor. Patients were classified as having essential tremor, essential tremor plus, or essential tremor-Parkinson's disease combination, and features between these groups were compared. Results:Of the 300 patients, 20.7% were classified as isolated essential tremor, 53.3% as essential tremor plus, and 26.0% as essential tremor-Parkinson's disease. There was no significant difference in the duration of tremor symptoms. Essential tremor plus patients were more likely to have dystonia, tandem gait abnormalities, head tremor and greater tremor severity. Essential tremor-Parkinson's disease patients were more likely to have RBD symptoms. There was no significant difference in cognitive impairment between essential tremor plus and essential tremor-Parkinson's disease patients.Conclusions: Additional motor and non-motor features, including parkinsonism, are common in patients with essential tremor. Further studies are needed to clarify essential tremor phenotypes and to provide insights into possible subtypes.Highlights: 300 patients with essential tremor from a movement disorders clinic were re-classified based on the Movement Disorder Society Consensus Statement on the Classification of Tremors. Additional motor and non-motor features, including parkinsonism, were common, and only 20.7% of patients remained classified as isolated essential tremor.

Tremor Syndromes: An Updated Review

“…There are no prevalence studies on this newly defined “ET” or “ET plus.” However, according to the previous diagnostic criteria, ET was one of the commonly observed movement disorders among adults. Several movement disorder centers have reclassified their ET patients using the new diagnostic criteria and have reported that ET plus outnumbers the isolated (pure) ET patients after such re-classification ( 8 – 10 ). As mentioned above, one of the core features of ET is action tremor (kinetic > postural) of both upper extremities.…”

“…There is growing body of evidence that some ET patients when followed longitudinally develop PD ( 10 , 18 , 19 ). Based on many clinical, epidemiologic, imaging, genetic and pathologic studies, a subset of ET patients appears to be at a high risk of developing PD.…”

“…Therefore, emergence of these NMS should prompt detailed evaluation to explore the possibility of PD or co-existent PD. The exact relationship between ET and PD is not well-understood but better understanding of the etiopathogenesis of ET and PD and their subtypes should lead to better insights into the relationships between these two common, but not well-defined movement disorders ( 10 , 18 ).…”

“…As discussed earlier, ET with additional neurological soft signs is now labeled as ET plus, as per the new tremor classification. This categorization has its own merits and limitations ( 10 ). The classification defines isolated ET which is helpful for genetic studies and for selection of a homogenous population of patients in interventional trials.…”

“…The introduction of ET plus group will have substantial impact on epidemiological studies. Indeed, since the publication of the Consensus statement, many studies have demonstrated that ET Plus is more prevalent than ET ( 6 – 10 ). In such scenarios, the significance of the previous clinical and epidemiological studies in which a large proportion of ET plus patients were categorized as ET, is going to be relatively uncertain ( 8 ).…”