By Arif Dalvi, MD, MBA
Palm Beach Neuroscience Institute
By definition essential tremor (ET) is a monosymptomatic disease with tremor as the only symptom and without an underlying cause in the form of other neurological diagnoses.
ET presents most commonly as a postural tremor of the hands, although a head or voice tremor are often seen. The presence of additional neurological signs and symptoms such as bradykinesia (slowness of movement), muscle rigidity or alteration in gait and balance point to an alternative diagnosis, most often Parkinson’s disease (PD) or parkinsonism. However, it is not uncommon for patients with a typical postural tremor to have poor balance, mild memory loss or even mild parkinsonian features.
Diagnosing ET and ET-Plus
There are two considerations in making the diagnosis in patients.
- About 6-10% of patients with ET will go on to develop superimposed PD after many years or even decades after having typical ET.
- Thought must be given to the possibility of what has been recently described in the medical literature as an essential tremor-plus (ET-plus) syndrome.
ET-plus refers to the presence of mild, neurological signs in addition to typical tremor. Parkinson’s disease or stroke should be ruled out prior to making this diagnosis.
There is some evidence that the ET-plus presentation is more common than isolated or classical ET. An ET-plus syndrome, with accompanying mild cognitive impairment and mild difficulty with balance in the form of ataxia, can also be observed in the setting of the Fragile X-associated tremor ataxia syndrome (FXTAS). Genetic testing for the FMR1 gene can help confirm FXTAS which, due to its association with the X chromosome, occurs predominantly in men.
Nonmotor Symptoms of ET
A number of nonmotor symptoms are described in association with ET. These include cognitive impairment, apathy, anxiety, depression, sleep disturbances and abnormalities in hearing and smell. Mild cognitive impairment may be seen in older ET patients beyond that expected for their age. Verbal fluency and verbal recall may be impaired. Cognitive impairment tends to be less severe in ET in comparison to Parkinson’s disease (PD). Anxiety and depression are also seen in many ET patients. Hearing loss is more frequent in ET than age-matched controls. Olfactory function (sense of smell), on the other hand, appears to be less affected compared to PD. Excessive daytime sleepiness is also seen in ET. While definite pathological correlates have not been determined for these nonmotor symptoms, their presence does support the understanding of ET as a neurodegenerative disease. Appropriate clinical examination of ET patients should therefore include evaluation of cognition, depression, anxiety and sleep disorders using appropriate rating scales.
Imaging the brain and/or spinal cord with MRI or CT can suggest alternative structural explanations for the ET-plus syndromes such as normal pressure hydrocephalus or vascular parkinsonism. In younger patients, a postural tremor in association with other neurological signs should prompt screening for Wilson’s disease, a disorder of copper metabolism with numerous neurological symptoms including tremor.
DaTscan imaging is not routinely required for a diagnosis of ET. However, in patients with an ET-plus syndrome, DaTscan imaging can help confirm superimposed PD leading to more appropriate treatment of symptoms such as bradykinesia and gait disorder. Alternatively, a therapeutic trial of carbidopa/levodopa can help solve the diagnostic conundrum.