Essential Tremor and Parkinson’s Disease: Exploring the Relationship

Abstract

BackgroundThere is longstanding controversy surrounding the possible link between essential tremor (ET) and Parkinson’s disease (PD). Inconsistent and unreliable diagnostic criteria may in part account for some of the difficulties in defining the relationship between these two common movement disorders.MethodsReferences for this systematic review were identified using PubMed with the search terms “essential tremor” AND “Parkinson’s disease” with articles published in English between 1960 and September 2018 included.ResultsIn this review we provide evidence that some patients diagnosed with ET have an increased risk of developing PD years or decades after onset of action tremor. There are several still unresolved questions about the link between the two disorders including lack of verifiable diagnostic criteria for the two disorders and marked overlap in phenomenology. Here we review clinical, epidemiologic, imaging, pathologic, and genetic studies that address the ET–PD relationship. Several lines of evidence support the association between ET and PD, including overlapping motor and non-motor features, relatively high prevalence of rapid eye movement sleep behavior disorder (26–43%) in ET patients, increased prevalence of PD in patients with longstanding antecedent ET, increased prevalence of ET in family members of patients with PD, and the presence of Lewy bodies in the brains of some ET patients (15–24%).DiscussionThere is a substantial body of evidence supporting the association between ET and PD within at least a subset of patients, although the nature and possible pathogenic mechanisms of the relationship are not well understood.

Functional Outcomes of Cerebellar Malformations

“…While previously thought of as a motor systems disease, PD has emerged as a syndrome encompassing a wide variety of etiologies with symptoms across behavioral domains (Jankovic, 2008; Michel et al, 2016). Similarly, ET, once defined as a benign tremor disorder, has increasingly been associated with non-motor symptoms (Bologna et al, 2019) and may herald more pervasive neurodegenerative disease (Laroia and Louis, 2011; Tarakad and Jankovic, 2018). In particular, patients suffering from either disease, PD or ET, are predisposed to depressive mood changes, sleep disruptions, and cognitive impairments (Puertas-Martín et al, 2016).…”

Brain TRODAT‐SPECT Versus MRI Morphometry in Distinguishing Early Mild Parkinson's Disease from Other Extrapyramidal Syndromes

“…As a result of overlapping symptoms and signs, differentiation between PD and ET might be occasionally challenging. The reported error rate in the clinical diagnosis of these disorders is about 24% 15,16 . In the early stages of PD, conventional brain magnetic resonance imaging (MRI) does not manifest any abnormalities and is only useful for excluding other diagnoses; however, volumetric MRI can quantify the volume loss in different parts of the brain of parkinsonian patients 17 .…”

Essential tremor: genetic update

“…6). Additionally, neurodegenerative changes such as Lewy bodies (LBs) reported in brains of some ET patients suggest the overlap between ET and PD (Refs 5–7).…”