Exploring the relationship between essential tremor and Parkinson's disease

Baylor College of Medicine, Houston, Texas, United States
Parkinsonism & Related Disorders (Impact Factor: 3.97). 04/2007; 13(2):67-76. DOI: 10.1016/j.parkreldis.2006.05.033
Source: PubMed


Although essential tremor (ET) and Parkinson's disease (PD) are considered distinct disorders, there is overlap in some clinical features. In some PD patients, a long-standing postural tremor in the hands may precede the onset of parkinsonian features by several years or decades. Furthermore, large families with both ET and PD phenotypes have been described and autopsy studies have demonstrated Lewy body pathology in brains of ET patients. Functional neuroimaging suggests that some ET patients have dopaminergic deficit. We examine here the evidence for and against an association between ET and PD, and critically review data supporting the notion that a subset of ET patients is predisposed to developing PD.

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Available from: Joseph Jankovic, Oct 13, 2014
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    • "The action tremor of Parkinson's disease occurs in a similar frequency band as patients with essential tremor making it difficult to use frequency analysis alone to distinguish a tremor associated with essential tremor from a tremor associated with Parkinson's disease (Sturman et al. 2005; Helmich et al. 2013). The action tremor of Parkinson's disease and essential tremor can appear similar to a physician, and the underlying pathophysiology that distinguishes these 2 diseases is not fully understood (Shahed and Jankovic 2007). Prior fMRI work examining the same grip task used in the current study has shown that the basal ganglia and M1 have a reduced BOLD signal compared with control individuals (Prodoehl et al. 2010; Spraker et al. 2010). "
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    ABSTRACT: It is well-established that during goal-directed motor tasks, patients with essential tremor have increased oscillations in the 0-3 and 3-8 Hz bands. It remains unclear if these increased oscillations relate to activity in specific brain regions. This study used task-based functional magnetic resonance imaging to compare the brain activity associated with oscillations in grip force output between patients with essential tremor, patients with Parkinson's disease who had clinically evident tremor, and healthy controls. The findings demonstrate that patients with essential tremor have increased brain activity in the motor cortex and supplementary motor area compared with controls, and this activity correlated positively with 3-8 Hz force oscillations. Brain activity in cerebellar lobules I-V was reduced in essential tremor compared with controls and correlated negatively with 0-3 Hz force oscillations. Widespread differences in brain activity were observed between essential tremor and Parkinson's disease. Using functional connectivity analyses during the task evidenced reduced cerebellar-cortical functional connectivity in patients with essential tremor compared with controls and Parkinson's disease. This study provides new evidence that in essential tremor 3-8 Hz force oscillations relate to hyperactivity in motor cortex, 0-3 Hz force oscillations relate to the hypoactivity in the cerebellum, and cerebellar-cortical functional connectivity is impaired.
    Full-text · Article · Jun 2014 · Cerebral Cortex
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    • "ET and PD are considered distinct disorders. However, an overlap of some clinical features in individual patients may appear [5]. Since the diagnosis of both ET and PD remains based only on the clinical criteria, many questions regarding a nosological association remain unanswered [4-11]. "
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    ABSTRACT: Essential tremor (ET) and Parkinson's disease (PD) are considered distinct disorders. The aim of the study was to look for a link or any distinguishing features by transcranial sonography (TCS), together with the clinical examination findings in a group of patients with overlapping phenotype of ET and PD (ET-PD). A prospective observational case-control study was carried out from the 3rd January 2011 until 30th January 2013 at the Hospital of Lithuanian University of Health Sciences. The final study group consisted of 15 patients with ET-PD, 116 patients with ET-only and 141 patients with PD-only. The control group included 101 subjects. Clinical diagnosis was of a diagnostic standard. The main ultrasonographic findings in the ET-PD group were similar to those of the PD-only: hyperechogenicity of the substantia nigra (66.7%, p < 0.001) and nuclei raphe interruptions/absence (38.5%, p < 0.001). The single distinguishing TCS finding in ET-PD group was a lentiform nucleus hyperechogenicity (26.7%), however this was only significant when compared to controls (p = 0.006). An asymmetrical onset of symptoms (73.3%) in ET-PD group was characteristic to PD-only. The ET-PD patients had the longest disease duration (median 6 years, p < 0.001), the most frequent rate of positive family history (53.3%, p = 0.005), rather low prevalence of cogwheel rigidity (26.7%, p < 0.001), and higher mean Hoehn & Yahr scores compared to PD-only (2.6 +/- 0.8 vs. 1.8 +/- 0.8, p = 0.012). The main TCS findings of the present study in patients with overlapping ET-PD phenotype were similar to the PD-only group. The highest positive family history rate among ET-PD patients indicates a strong hereditary predisposition and needs genetic underpinnings. Some ET patients, who look like they may be developing co-morbid PD clinically, may have an alternative diagnosis for Parkinsonism, which could be delineated by TCS examination.
    Full-text · Article · Mar 2014 · BMC Neurology
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    • "The ongoing attempts to untangle ET and PD117–119 can be viewed from a genetics research perspective. Pragmatically, cases with both ET and PD (ET–PD) are well reported. "
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    ABSTRACT: Genetics research is an avenue towards understanding essential tremor (ET). Advances have been made in genetic linkage and association: there are three reported ET susceptibility loci, and mixed but growing data on risk associations. However, causal mutations have not been forthcoming. This disappointing lack of progress has opened productive discussions on challenges in ET and specifically ET genetics research, including fundamental assumptions in the field. This article reviews the ET genetics literature, results to date, the open questions in ET genetics and the current challenges in addressing them. SEVERAL INHERENT ET FEATURES COMPLICATE GENETIC LINKAGE AND ASSOCIATION STUDIES: high potential phenocopy rates, inaccurate tremor self-reporting, and ET misdiagnoses are examples. Increasing use of direct examination data for subjects, family members, and controls is one current response. Smaller moves towards expanding ET phenotype research concepts into non-tremor features, clinically disputed ET subsets, and testing phenotype features instead of clinical diagnosis against genetic data are gradually occurring. The field has already moved to considering complex trait mechanisms requiring detection of combinations of rare genetic variants. Hypotheses may move further to consider novel mechanisms of inheritance, such as epigenetics. It is an exciting time in ET genetics as investigators start moving past assumptions underlying both phenotype and genetics experimental contributions, overcoming challenges to collaboration, and engaging the ET community. Multicenter collaborative efforts comprising rich longitudinal prospective phenotype data and neuropathologic analysis combined with the latest in genetics experimental design and technology will be the next wave in the field.
    Full-text · Article · Jan 2013
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