This review describes the most recent advances in epidemiology, classification, genetics, pathology and treatment of essential tremor. In addition, recent advances in more rare forms of tremor are summarized.
Clinical, biochemical, pathological and imaging studies suggest an abnormal functioning of the cerebellum in essential tremor. Minor changes of cognition and personality may be due to secondary effects. Dementia and possible shortened life span seem to be limited to late-onset essential tremor. Many of these issues are not yet finally settled and need confirmation in further studies. The current essential tremor classification seems not to reflect the variety of phenotypic expressions. Regarding treatment, there is now a level B evidence for topiramate. Levetiracetam may induce a positive response in Holmes tremor, but is ineffective in orthostatic tremor.
These findings have extended our knowledge about essential tremor. It appears that a new, more distinct classification system is required. Recent treatments have remained unchanged.
"Despite its high prevalence, ET pathogenesis remains poorly understood. Clinicopathological and neuroimaging investigations in ET patients have pointed out different types of anomalies in the cerebellum that could be involved in tremor generation (Zeuner and Deuschl, 2012; Louis, 2014). For example, a reduction in the number of Purkinje cells (PC) together with axonal morphometric changes have been described in the cerebellum of a significant subgroup of ET patients (Louis et al., 2007, 2013), but PC loss was not detected in all ET studies (Rajput et al., 2012; Symanski et al., 2014), possibly due to methodological differences (Louis and Faust, 2014). "
[Show abstract][Hide abstract] 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.
"suggest that adding load to the tasks contributes to clearing out a distinction between the profiles of tremor modulation for PDs, ETs and controls. This has been reported in the literature , though the impact of adding a load to the wrist cuff or arm to modulate tremor is still object of debate, mostly due to the role that might be played by the antagonist muscles that are not affected by the load but are able to interfere with tremor quantification when for example, the EMG is used to characterized tremor   . Taking the time evolution of tremor measures as an indicator of the level of tiredness of the participants when performing the tasks, our results show that all participants tolerate the effort on both task 3 and 4, to which the analysis was restricted. "
[Show abstract][Hide abstract] ABSTRACT: Tremor is a manifestation of a variety of human neurodegenerative diseases, notably Parkinson’s disease (PD) and Essential Tremor (ET), both affecting millions worldwide. PD is primarily caused by a progressive loss of dopamine neurons in the nigrostriatal system that leads to widespread motor symptoms such as bradykinesia, rigidity, tremor and postural instability. ET typically involves a tremor of the arms, hands or fingers. No definitive test or biomarker is yet available for PD or ET, so the rate of misdiagnosis is relatively high. As tremor is a very common feature at the onset of both diseases, it is crucial to be able to characterize it. This is made possible using acce?lerometers to quantify the tremor amplitude and frequency. In this work we aim to find tasks involving upper limb movements that are suitable to modulate both types of tremor. Four tasks were tested, differing on whether the arms moved together or alternatingly and whether loads were added. Significant differences in tremor measures were found when patients were asked to perform simultaneous rapid arms movements with loads placed on their wrists. These results may allow the design of an efficient fMRI protocol for identifying the cortical circuits responsible for the modulation of tremor.
Neuroscience & Medicine 01/2014; 05(05-05):205-213. DOI:10.4236/nm.2014.55024
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