Essential tremor (ET) is the most common movement disorder. ET’s often called Benign Essential Tremor, because it usually doesn’t result in marked or striking disability. Few ET patients become disabled; most are able to cope.
ET’s sometimes called Familial Tremor, or Hereditary Tremor, or Heredito-Familial Tremor because in approximately 50% of patients there’s a family history. ET’s sometimes called Senile or Senescent Tremor because it usually occurs in senior citizens. Senile or Senescent refers to the age at ET occurs, not to the patient’s mental capacity. Because of the misleading association of the terms senile or senescent tremor with senility or mental decline the term Senile or Senescent Tremor isn’t used.
ET’s a chronic disorder characterized by involuntary rhythmical trembling or oscillation of a body part – usually the hands. The trembling usually begins on both sides symmetrically unlike the trembling of PD which begins on one-side. ET may begin insidiously with the patient unaware of (or in denial of) of the trembling until it’s pointed out. ET usually begins in the 2nd, 3rd, 4th or 5th finger – where it’s apt to go un-noticed. This is unlike the trembling of PD which usually begins in the thumb and is more apt to be noticed. The trembling in ET may, for years, remain unchanged in amplitude, frequency and distribution. Or the trembling may slowly change in amplitude and distribution. Or the trembling may increase in amplitude and distribution. The changes are rarely rapid or striking.
The trembling in ET may, in some patients, affect the head, the voice (as the vocal cords or tongue tremble), the legs or the trunk. In some patients trembling may begin in the head, the voice, or the tongue. The trembling in ET rarely begins in the legs. Trembling that begins in an arm and a leg on the same side of the body, or in the jaw is more likely to be PD.
Trembling of the hand is the most common symptom of ET. The trembling involves flexor and extensor muscles – and consists of rhythmical up-and-down movements. Rarely the trembling has a rotatory component. The trembling begins bilaterally and symmetrically. However, in approximately 10% of patients the trembling begins in one hand. In ET, the frequency of the trembling is 4-12 cps (or hertz). The frequency varies from patient-to-patient but is constant in an individual patient.
In most ET patients the trembling worsens (or first becomes visible) when the patients voluntarily maintains his hands in a fixed posture or position as in holding his hands stretched in front of him. This type of trembling is called a postural tremor.
In some ET patients the trembling worsens (or first becomes visible) when the patient voluntarily moves his hands as in performing an action such as bringing a glass of water to his lips, tying his shoes, or threading a needle. This type of trembling is called an action, or a kinetic, or a movement tremor. Most ET patients exhibit both postural and action trembling. In those ET patients who exhibit both postural and action trembling – postural trembling usually dominates.
In a few ET patients the trembling worsens (or first becomes visible) as the patient, in performing a goal-directed voluntary movement, as in taking his finger and touching his nose, approaches the goal (his nose). This type of trembling is called an intention tremor. A few ET patients exhibit a postural, a kinetic, and an intention tremor. In these patients the postural trembling dominates. Some ET patients exhibit an action and an intention tremor. In these patients the action trembling dominates.
A few ET patients exhibit only an intention tremor. Usually, but not always, an isolated intention tremor, one not associated with a postural or action tremor, indicates disease or dysfunction of the cerebellum.
The cerebellum is an oval structure approximately 1/10th the volume of the brain (or cerebrum). The cerebellum sits below the brain and behind the brainstem. The name, cerebellum, means "little brain." The cerebellum regulates movement and balance.
Rarely, ET patients exhibit trembling at rest, trembling when the hands are relaxed and not moving. This type of trembling is called a rest tremor. In ET patients who exhibit rest trembling, the trembling is never isolated – it’s always associated with postural or action trembling. Isolated rest trembling, especially confined to one side-of-the-body, indicates PD. All trembling, ET trembling, cerebellar trembling, and PD trembling disappear during sleep.
Uniform criteria aren’t agreed upon. The following, however, are useful in diagnosing ET and excluding other causes of trembling.
Estimates regarding ET’s prevalence vary. This is so because there’s disagreement on diagnosing ET. A study that includes physiological tremor with ET will come to a different conclusion from one that distinguishes physiological tremor from ET. The prevalence of ET increases with age. A study that surveys people in a retirement community will come to a different conclusion from one that surveys people in a college town. A study that surveys people attending a movement disorder clinic (one that attracts ET patients) will come to a different conclusion from one that surveys people in a general medical clinic.
Among people of all ages, the prevalence of ET varies from 4,000 to 40,000 patients per million of population (a 10-fold difference). Among people of age 60+ years, the prevalence of ET varies from 13,000 to 50,000 patients per million of population. ET may affect as many as 10 million Americans, 3.7% of the population. ET’s 20 times more common than Parkinson disease (PD). Although almost all PD patients see a doctor and half see a movement disorder specialist, perhaps less than 1% of ET patients see a doctor. For every 10 PD patients who see a movement disorder specialist, one ET patient sees a movement disorder specialist. This reflects the benign course of ET. ET affects males and females equally. In some patients, ET begins in adolescence.
In ET patients, as time passes, the trembling in most patients, but not all, increases. And, ET patients develop varying degrees of disability. The disability results solely from the trembling. This is unlike PD where the disability results mainly from the slowness of movement and/or the rigidity and less from the trembling. In ET the trembling increases and worsens over decades.
Although anxiety or stress may temporarily increase the trembling, a sudden and persistent increase in trembling indicates a super imposed disease: an electrolyte or hormonal imbalance, an adverse effect of a drug, Parkinson disease.
Eventually, ET patients may develop difficulty performing everyday tasks such as holding or manipulating small objects, tools, or utensils. ET patients may have difficulty writing, drinking water from a cup or glass, feeding themselves, applying make-up, shaving, or dressing.
In ET patients, after the hands, the most frequently affected body part is the head, followed by the voice, tongue, palate, legs, or trunk. Head, voice, tongue, palate, leg, or trunk trembling may occur in isolation or maybe associated with trembling of the hands. Jaw trembling as distinct from head trembling is usually a symptom of PD not ET. In ET patients the head trembling usually, 75% of the time, occurs in a horizontal plane and is called a "no-no" tremor. Sometimes the head trembling occurs in a vertical plane and is called a "yes-yes" tremor. And sometimes the head trembling occurs in a horizontal and vertical plane and is called a "complex" tremor. In most ET patients with isolated head trembling, the head trembling results from dystonia not ET.
In some ET patients, as the trembling of the voice, tongue, and palate increases and worsens, speech becomes "tremulous" or "shaky" and may be difficult or impossible to understand. Such speech is called "dysarthria". In ET patients dysarthric speech, if it occurs, occurs after age 65 years. In ET dysarthric speech is rare below age 65 years – and when it occurs below age 65 years causes other than ET should be sought.
In ET patients the psychological and social effects of the trembling is embarrassing, can be un-nerving, and may be devastating. Among lay-people unfamiliar with ET, trembling in an otherwise normal appearing individual suggests alcoholism or drugs. ET because it’s physically less debilitating than PD has received less publicity than PD. More people have ET than PD – yet it’s difficult to name several famous people with ET. ET patients are better able to disguise their disability. ET may, in some patients, lead to withdrawal from social life because of embarrassment.
In 1994, the Essential Tremor Study Group reported on the relationship of ET to other movement disorders. The Group evaluated 678 ET patients. Among the 678 patients, 6.1% had PD, 6.9% had dystonia (a sustained abnormal contraction of muscles) and 1.8% had myoclonus (an intermittent and usually rhythmical jerking of a limb or limbs).
The Group concluded that the frequency of PD among individuals with ET is greater than would be expected in the general population. Many, but not all, experts believe there’s a relationship between PD and ET, that ET patients are more likely to develop PD. Others believe ET and PD are part of a spectrum.
Many, but not all, experts believe there’s a relationship between dystonia, myoclonus, and ET. Dystonia’s less common than ET. While 6.9% of ET patients have dystonia, 25%-50% of dystonia patients have ET. Other experts disagree. They consider the head and/or the hand tremor of dystonia as distinct from ET. Some ET patients, especially those 75+ years of age, are unsteady when walking.
The postural and/or action trembling seen in 25% of PD patients, the postural trembling seen in dystonia, and the postural and/or action trembling of ET may be sorted-out from each other by recording the trembling with an accelerometer, by recording the activity of the contracting muscles with an electro-myogram (EMG), and by correlating the activity of the accelerometer and the EMG.
In many patients ET’s inherited. But how an inherited defect results in trembling is unknown. Examination, after death, of the brains of ET patients is normal. It’s been proposed that abnormalities in specific brain structures: the olives, the cerebellum, the thalamus result in these structures acting as oscillators, setting-up self-propagating currents, resulting in trembling.
, an anti-convulsant, a drug used in epilepsy, can reduce the severity of trembling in ET. Primidone’s long acting. The starting dose is 25 mg given at night. The dose is gradually raised to 250mg at night. If a patient doesn’t improve, the dose is raised gradually to 250 mg every 8 hours. Primidone should be given with meals to minimize stomach distress. Approximately 70% of ET patients improve, to varying degrees. If a patient doesn’t improve, primidone should be discontinued – gradually. Primidone’s a barbiturate, like phenobarbital, and abrupt withdrawal may cause convulsions.
Primidone’s main side effect is drowsiness. This may limit treatment. Additional side effects may include unsteadiness, irritability, decreased appetite, and decreased sexual desire. Many of side effects eventually disappear.
a beta-blocker, a drug used to control high blood pressure or slow a rapid heart rate, can reduce the severity of trembling in ET. Beta-blockers inhibit or block the actions of adrenalin on blood vessels and the heart. The starting dose is 40mg twice-a-day. The dose may be gradually raised to 120 mg three times-a-day. Approximately 50% of ET patients improve, to varying degrees. If a patient doesn’t improve, propranolol should be stopped--gradually. Propranolol and other beta-blockers may be inappropriate for patients with certain heart problems, insulin-dependent diabetes, certain types of lung problems including asthma, and vascular disease.
Possible side effects of propranolol therapy include dizziness, fatigue, depression, nausea, and impotence. These side effects are reversible upon stopping propranolol. Some patients develop a tolerance for primidone and/or propranolol and primidone. Primidone and propranolol may be used in combination.
Other Drugs:
Surgery is an option for patients with incapacitating tremor unresponsive to medication: primidone and propranolol. There are two types of surgery:
In ET the procedure of choice is DBS of the thalamus. Whether DBS should be done on one-side or both-sides requires a determination of how incapacitating the tremor in each hand is.