What is Essential Tremor, how is it evaluated and how is it treated?
Aparna Wagle Shukla, M.D., Physician and Research Scientist at the University of Florida Center for Movement Disorders
What is Essential Tremor?
Essential tremor (ET) is the most common movement disorder encountered in expert clinics. Family history is often positive and thus ET is frequently referred to as a benign tremor or familial tremor, though it is not benign. The typical age of onset is either in early 20s and 30s or in the late 60s and 70s. Men and women are affected equally. Tremors in many cases are mild but can cause significant functional limitation of the activities of daily living, such as writing, eating, drinking or dressing. Essential tremor increases in frequency with age, and is present in more than 1% of individuals 70 years of age or older. Tremors typically worsen with emotional and physical stress. Alcohol is found to alleviate the tremors in some, but not all cases; and the underlying mechanism is not clear. Although response to alcohol is important for clinical diagnosis, it is not recommended as a treatment. Essential tremor like Parkinson’s disease is now considered a neurodegenerative disease, however the speed of progression is extremely slow and the disease course can sometimes run for many decades. In the later stages of disease, tremors are noted to become more severe, there is a wider distribution and there may be changes in the gait and cognition of the affected individuals.
What is the difference between Essential Tremor and Parkinson Disease tremor?
How is Essential Tremor evaluated?
Essential tremor most commonly affects the arms, tremors are typically asymmetric in the beginning and with advancement, tremors of other regions, notably the head, face, voice, trunk, and legs, are seen either separately, or in combination. There is also a general rule, if prominent tremors are seen in the legs, Parkinson’s disease should be ruled out.
Diagnosis of essential tremor is based on specific criteria observed during the clinical exam. These criteria include the presence of tremors in both hands and forearms engaged in routine daily tasks and absence of any additional neurologic symptoms or signs. A bedside physical exam involves observation of tremors during postural elevation of the arms, on kinetic tasks like drawing an Archimedes spiral (See Figure), line drawing, writing, pouring water into glass and on intentional maneuver such as finger-to nose testing. Tremors occur mainly in the distal hands and are 4 to 12 Hz in frequency, but this can be widely variable. Tests such as those shown below are ways in which a physician can evaluate and monitor tremor.
Sometimes during the passive movement of the forearm, a cogwheeling type of resistance is felt by the physicians resulting in a mistaken diagnosis of Parkinson’s Disease. This type of resistance is felt particularly in older individuals. However, in Parkinson’s Disease tremors in the hands are present mainly at rest, tremors are classically but not always pill rolling in character, tremors are unilateral or asymmetric in presentation, tremors in legs are prominent, and there are other pertinent accompanying symptoms such as slowness, lack of dexterity in the hands, stiff muscles, softening of speech, lack of expression on the face, shuffling gait and postural instability. It is possible however to have a resting tremor in essential tremor.
Another important differential diagnosis for essential tremor is enhanced physiologic tremor that is sustained as a result of either an identifiable cause, such as medication or hyperthyroidism; or a cause that is not readily identifiable. Caffeine, cigarettes, and medications such as lithium, prednisone, levothyroxine, beta-adrenergic bronchodilators, valproate, and selective serotonin-reuptake inhibitors commonly result in these enhanced physiologic tremors. Adult-onset idiopathic dystonia, and Wilson’s disease are other conditions on the list that are particularly applicable to younger individuals. Physicians should ask the necessary questions to distinguish these pertinent differential diagnoses.
Although at present there are no validated serologic, radiologic, or pathological markers for diagnosis, major initiatives are actively being explored. Recently an imaging technique known as DaTscan™ (125I-iofluane SPECT), which measures the integrity of the dopamine system in the brain was approved by the FDA, to help distinguish ET from PD. At University of Florida, Dr. Vaillancourt and colleagues are conducting a major NIH sponsored study to investigate the role of functional MRI (fMRI) and diffusion tensor imaging (DTI) in the diagnosis of essential tremor. These techniques follow well established imaging methods. The functional MRI has an ability to look at the brain activity based on changes in regional blood flow, whereas DTI is used to examine changes in brain connectivity by measuring water diffusion along nerve fiber tracts in the brain. University of Florida also offers a quantitative computerized analysis of tremor that can helps distinguish essential tremor from other types of tremor. This technique is simple, noninvasive, and can be scheduled in the physiology laboratory on an as needed basis.
How is Essential Tremor treated and managed?
At present there is no cure for essential tremor, but tremors can be alleviated with multiple therapies. Mild tremors may not require pharmacological treatments and can be addressed with various non-pharmacological techniques. These techniques include the use of weighted utensils or application of weights to the wrists during daily functional tasks to reduce the amplitude of tremors. These weights are available at stores such as Walmart and Target, or can be ordered online. Another non-pharmacological approach is use of cooling the arms; a technique also used for the control of tremors. All of these techniques can successfully control some of the tremors in although the benefits are short-lasting for some patients. At University of Florida, clinicians routinely schedule essential tremor patients with an occupational therapist for evaluation and demonstration of these techniques.
Propranolol and primidone are the mainstays of medical treatment. Multiple studies have documented the efficacy of propranolol and primidone in the treatment of hand tremors, although these medications have less efficacy for control of tremors located in the head, voice, leg, and trunk. In the early stages these medications are effective in reducing the amplitude of tremors roughly in the range of 40-50% but over time they may lose efficacy. Sometimes a combination of these two drugs can be tried to facilitate greater synergistic benefits. The potential benefit of these therapies should be weighed against the possible side effects. Side effects of the medications should always be explained before initiation of therapy. Propranolol is known to result in slowing of the heart rate, fatigue, worsening of diabetes, worsening of mood and exacerbation of asthma. Primidone on the other hand is found to cause worsening of gait, balance, sleepiness and behavioral issues in some individuals. If tremors continue to remain inadequately controlled, a trial of a second-line medication, such as benzodiazepines, gabapentin, topiramate, or botulinum toxin, can also be tried. Finally, for select cases of medication refractory disabling tremors, deep brain stimulation (DBS) of the thalamus is the new standard of care. DBS surgery is now well established and FDA approved. More than 100,000 surgeries have been performed worldwide and several studies have proven its effectiveness in control of essential tremors. DBS will not stop progression of the tremor and in some cases there may be speech and walking related side effects. The University of Florida offers each of these therapies through its integrated multidisciplinary program.
In conclusion, essential tremor is a slow progressive disease, has clear well-established guidelines for diagnosis and can be treated by nonpharmacological, pharmacological and surgical approaches.