[Essential tremor: are we just splitting hairs? Non-motor symptoms and essential tremor-plus].

Introduction: The existence of non-motor symptoms in essential tremor (ET) and the appearance of a new condition, ET-plus, are two controversial issues.

Aims: To offer a review of the current status of these two topics.

Development: We performed an analysis of the studies conducted on non-motor symptoms in ET and of the articles for and against the use of the term ET-plus.

Conclusions: Non-motor symptoms have gained increased recognition as a feature accompanying ET. Several studies have documented its presence compared to matched controls. It is not clear, however, whether these non-motor symptoms would be part of the spectrum of ET symptoms (a primary phenomenon) or whether they would be symptoms that appear as a consequence of the physical or psychological disability produced by the clinical signs and symptoms of ET itself (a secondary phenomenon). For the time being, their evaluation and treatment are not included within the standard assessment of patients with ET. In view of the heterogeneous phenotype, the term ET-plus aims to improve phenotypic homogeneity for genetic or therapeutic studies. Yet, there is no pathological basis, and epidemiological, genetic and therapeutic research studies have numerous drawbacks. In the absence of clear objective biomarkers, distinguishing between ET and ET-plus by clinical distinction alone is very complex. We should be cautious about using new terms that are not yet backed by sound scientific evidence.