Investigations
1st investigations to order
clinical diagnosis
Test
There are no validated serological, radiological, or pathological markers of ET, and, therefore, the diagnosis remains a clinical one.
Result
bilateral tremor with normal muscle tone and speed of movement; negative history and examination for Parkinson's disease, hyperthyroidism, medications, and alcohol use
Investigations to consider
CT or MRI scan of the head
Test
Currently, the role of neuroimaging techniques, such as CT or MRI of the head, in patients with suspected essential tremor is limited in daily practice because unremarkable scans are expected.[77]
However, imaging work may be useful to distinguish ET from other types of tremor.
Neuroimaging is particularly indicated when the patient has a focal neurological sign, which would not be due to ET, and which therefore suggests an alternative pathological process such as a focal lesion within the central nervous system (CNS).
Result
normal
serum ceruloplasmin
Test
This test is indicated for patients <40 years of age with parkinsonism, dysarthria, or dystonia, to rule out other types of tremor.[13]
A low serum ceruloplasmin (<200 mg/L [20 mg/dL]) indicates Wilson's disease.
Result
normal
24-hour urine copper
Test
Indicated for patients <40 years of age with parkinsonism, dysarthria, or dystonia. A high level (>100 micrograms) indicates Wilson's disease.
Result
normal
thyroid function tests
Test
This test is performed in patients with signs or symptoms of hyperthyroidism, such as diarrhoea, tachycardia, and/or exophthalmos.
Result
normal
tremor physiology studies
Test
Surface electromyography (EMG) recording from one or both hands, agonist and antagonist muscles, together with a triaxial accelerometer. Testing usually includes at least 2-minute recordings of resting, postural, and kinetic conditions, and may also include weights or entrainment protocol (e.g., providing an audible metronome rhythm at varied frequencies; asking the patient to make rhythmic movements at a given frequency with the unrecorded limb).
In the presence of a severe action tremor it can sometimes be difficult to distinguish a true rest tremor from a tremor at rest (which occurs when tremor is seen in a resting position but the arm is not completely supported against gravity).
Result
electromyographic silence in all the other muscle groups except the tremulous agonist-antagonist pairs, which show no background electromyographic activities other than rhythmic contractions; the frequency of the main component remains unchanged when a weight is placed on the affected limb; tremor frequencies may shift under entrainment but can always remain at a frequency different from the entrainment target frequency; frequency range 8-12 Hz
single-photon emission CT (SPECT) scan of the head
Test
There is evidence to suggest that I-123 (DaTscan) SPECT studies may be useful in differentiating ET from Parkinson’s disease, with ET patients having a normal putamen value on scanning.[75]
Result
normal
Emerging tests
tremor stability index
Test
A tremor stability index (TSI), which is derived from the kinetic measurement of tremor, has been proposed to differentiate ET and Parkinson’s disease tremor.[76]
It has a maximum sensitivity of 95%, specificity of 95%, and diagnostic accuracy of 92%.[76]
Result
TSI values >1.05 indicate a diagnosis of ET; TSI values <1.05 indicate a diagnosis of Parkinson's disease
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