Progress and Prospects in Parkinson's Research/Atypical Parkinsonism/Essential-Tremor

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"Essential Tremor (ET) is a movement disorder which is sometimes diagnostically confused with the resting tremor which is a signature symptom of PD."

Background
This tremor affects the upper limbs initially and can spread to other parts of the body. It occurs when there is ongoing muscular activity unlike the PD tremor, which occurs at rest. It can be brought on or intensified by psychological stress. The frequency is from 4 to 12 Hz.

Research
2008

Louis evaluated the epidemiology of ET.

"The development of PD has often been described in ET patients. In recent studies, ET patients were 2–4 times more likely to develop PD (that is, ET plus PD) when compared to persons without ET. ET-like action tremor is more common in PD families than control families, further supporting the links between ET and PD, and postmortem studies have now shown that a subset of ET patients has brainstem (mainly in the locus ceruleus) Lewy bodies."

2010

Schwingenschuh et al carried ut a detailed study of a oohort of patients designated as SWEDDs (Scans Without Evidence of Dopaminergic Deficit).

We used transcranial magnetic stimulation with a facilitatory paired associative stimulation (PAS) paradigm to test if sensorimotor plasticity in SWEDDs resembled the pattern seen in PD, dystonia or ET.....

''...A combination of re-emergent tremor and highest tremor amplitude in the resting condition was characteristic of PD tremor, while SWEDDs, dystonia and ET subjects had the highest tremor amplitude during action. Both SWEDDs and segmental dystonia patients exhibited an exaggerated pattern of sensorimotor plasticity in response to the PAS paradigm, with spread of excitation to an adjacent hand muscle. In contrast, PD patients showed no response to PAS, and the response of ET patients was no different from controls. Taken together, these results may help differentiate these SWEDDs patients from PD and support our hypothesis that adult-onset dystonia is the underlying diagnosis in this sub-group of patients with SWEDDs.''