Objective: To compare the incidence of the different tremor syndromes using 1998 versus 2018 consensus criteria for classifying tremor disorders.

Background: In 1998, the Consensus Statement on Tremor issued by the Movement Disorder Society (now called the International Parkinson Disease and Movement Disorder Society [IPMDS]) classified the different tremor disorders [1]. Twenty years later, the IPDMS published new consensus criteria, mainly due to subsequent advances in essential tremor, tremor associated with dystonia and other monosymptomatic and indeterminate tremors [2]. Tremor syndromes are specific combinations of clinical signs and symptoms that commonly coexist.

Method: We conducted a retrospective review of all patients referred to our Movement Disorders Unit due to tremor between 2003 and 2018. We reviewed the tremor syndrome in the first visit according to the 1998 consensus criteria. Afterwards, the new 2018 consensus criteria were applied to each patient.

Results: Data of 1,001 patients were obtained, 513 (51.2%) were women and the mean (SD) age at the first visit was 70.06 (11.88) years (range 19-98). Considering 1998 criteria vs 2018 criteria, 422 (42.2 %) vs 457 (45.7 %) patients met criteria of parkinsonian tremor syndrome, 307 (30.7%) vs 181 (18.1%) of classic essential tremor (ET), 66 (6.6%) vs 141 (14.1 %) of enhanced physiologic tremor syndrome and 16 (1.6%) vs 59 (5.9%) of indeterminate tremor, respectively. Both criteria diagnosed the same number of dystonic tremor, orthostatic tremor, psychogenic tremor and Holmes’ tremor. Considering 1998 criteria, we diagnosed 129 (12.9 %) patients of drug-induced and toxic tremor syndromes that according to the 2018 criteria were included in the enhanced physiological tremor or in parkinsonism associated with tremor. Considering 2018 criteria, 61 (6.1%) patients met criteria of isolated segmental action tremor, 23 (2.3%) of ET plus, 19 (1.9 %) of focal tremor and 14 (1.4%) of isolated rest tremor.

Conclusion: Using 2018 criteria, the incidence of ET was lower, probably because the new definition of ET requires at least a 3-year history of tremor and excludes isolated head and isolated voice tremors so that patients were classified as isolated segmental action tremor, focal tremor or indeterminate tremor. However, the incidence of enhanced physiologic tremor increased to include the drug-induced and toxic tremor syndromes considering the 1998 criteria.

References: [1] Deuschl G, Bain P, Brin M. Consensus statement of the Movement Disorder Society on Tremor. Ad Hoc Scientific Committee. Mov Disord 1998;13(Suppl 3):2-23. [2] Bhatia KP, Bain P, Bajaj N, Elble RJ, Hallett M, Louis ED, Raethjen J, Stamelou M, Testa CM, Deuschl G; Tremor Task Force of the International Parkinson and Movement Disorder Society. Consensus Statement on the classification of tremors, From the task force on tremor of the International Parkinson and Movement Disorder Society. Mov Disord. 2018 Jan;33(1):75-87.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-impact-of-the-new-classification-criteria-on-the-incidence-of-tremor-syndromes/