Tremor, the most common form of abnormal involuntary movement (AIM), is a rhythmic oscillation of a body region produced by alternating contractions of reciprocally innervated muscles.1, 2 It occurs across a wide spectrum of neurological disorders and is easily distinguished from other AIMs such as chorea, tics, and myoclonus by its rhythmic, repetitive and stereotypical appearance. Tremor causes not only discomfort and social embarrassment for patients, but also disability. Since successful treatment depends on the correct diagnosis, it is important for the clinician to recognize the various presentations of tremor and associated symptoms. This article describes the general clinical approach to the patient who presents with tremor and reviews the most common tremor syndromes and their management.
CLASSIFICATION OF TREMOR
When evaluating a patient who presents with tremor, first categorize the tremor based on its positional properties. Tremor can be divided into two main types: rest and action. Rest tremor occurs in a body part that is relaxed or supported against gravity and not involved in purposeful activities, for example, a hand tremor evident when the upper limb rests on the arm of a chair. When intermittent or minimal, a rest tremor can be brought out or enhanced on examination by having the patient concentrate on other tasks, such as performing arithmetic or opening and closing the contralateral hand. The presence of a rest tremor is virtually synonymous with parkinsonism, a condition with multiple etiologies, including drug-induced (due mainly to neuroleptics) and other neurodegenerative disorders such as multiple system atrophy (MSA) or progressive supranuclear palsy (PSP). Parkinson's disease (PD), however,, is by far the most common cause of parkinsonism, comprising approximately three quarters of all cases seen in movement disorders centers.3
Action tremor is present during the voluntary contraction of muscles, and can be subdivided into four types: postural, kinetic, isometric, and task-specific. Postural tremor is seen during the maintenance of an anti-gravity posture, such as when a patient holds a newspaper up to read, whereas kinetic tremor happens during voluntary movement. Often brought out using the fingernose-finger test, a kinetic tremor can occur at the beginning of the movement, during the course of the movement, or when approaching a target. In the latter condition, it is also known as an intention tremor, commonly seen with cerebellar lesions. Isometric tremors are present during voluntary muscle contractions not accompanied by movement, for example, when standing or when making a fist. Task-specific tremors, as the name implies, occur only during specific activities, such as writing, singing, or playing an instrument. The postural and kinetic tremor subtypes are seen far more frequently than the isometric and task-specific subtypes.
Just as each tremor type has multiple etiologies, more than one tremor type can occur in the same condition. For example, PD patients often have an action component in addition to their classic rest tremor, while the postural tremor seen in essential tremor (ET) can sometimes persist when the hands rest in the patient's lap. Though this overlap can sometimes cause difficulty for the diagnosing clinician, a tremor that diminishes with voluntary movement is likely to be a rest tremor, while a tremor rhat is present at rest but worsens with movement is probably an action tremor.
CLUES TO THE DIAGNOSIS OF TREMOR
Once the predominant type of tremor is identified, a short differential diagnosis can be generated (Table 1) and narrowed down based on clues obtained from the clinical history and neurological examination. Historical elements that are important to elicit include: 1) age at onset of the tremor, 2) mode of onset (sudden vs. gradual), 3) anatomical site(s) affected by the tremor, 4) rate of progression to other sites, 5) exacerbating and remitting factors (such as alcohol responsiveness), 6) history of alcohol abuse, and 7) family history of tremor. Furthermore, many pharmacologie agents can cause tremor (Table 2), so a thorough review of the patient's medications is essential. Associated examination findings that may shed light on the underlying etiology of the tremor include bradykinesia or rigidity (PD); nystagmus, scanning speech, ataxia (cerebellar lesion); and a wide variation in tremor frequency (psychogenic).
If the diagnosis can be established on clinical criteria and the patient responds to treatment, ancillary studies are usually unnecessary. However, in young patients (
COMMON TREMOR SYNDROMES AND THEIR MANAGEMENT
The most common tremor syndromes encountered in clinical practice are ET and PD. Although cerebellar and psychogenic tremors are less frequently seen, they are important for the general clinician to be aware of and will be briefly reviewed. Iatrogenic causes of tremor are common, and may even mimic ET or PD. If a patient is taking a medication known to induce tremor (Table 2), that medication should be discontinued before initiating other therapy.
ESSENTIAL TREMOR (ET)
ET is the most common movement disorder.2 The diagnosis can be made when a persistent, bilateral, mainly symmetrical, postural and/or kinetic tremor of the hands or arms is present, without other neurological signs or exposure to drugs that may cause tremor.5 A head tremor can also be part of the syndrome, either in addition to the hand tremor or in isolation, as long as there is no dystonic posturing. Clinical or historical features consistent with a diagnosis of ET include a positive family history and improvement of the tremor with alcohol, but these features are not present in every patient. Although ET can occur at any age, its prevalence generally increases with age.
ET tends to start distally in the arms with a typical flexion-extension motion at the wrists or abduction-adduction movement of the fingers. Although it may be unilateral in onset, both sides will eventually be involved. The most common anatomical sites of involvement after the hands are (in decreasing order) the head, voice, legs, and chin.6 The tremor tends to increase with stress, anxiety, excitement, emotional upset, fatigue or cold temperature. Although ET is sometimes preceded by the term "benign", many patients dispute the adjective. ET causes both physical and social disability. Simple tasks such as signing a check, eating, drinking from a cup, shaving, brushing teeth, and dressing can become frustrating ordeals, and embarrassed patients often avoid social situations.
Primidone (Mysoline) andpropranolol (Inderal) continue to be the mainstays of treatment for ET. Primidone, an anticonvulsant, may be the more effective agent, with approximately 70% of patients experiencing benefit, compared to 50% of patients on propranolol.7 Though dosages between 50 and 250 mg of primidone daily are usually needed to reduce tremor,8 this medication should be started at a low dose and titrated slowly up in order to minimize adverse effects. Primidone is usually prescribed in one single daily dose at bedtime, beginning with 25 mg, and increased by 25 mg weekly until the desired tremorlytic effect is obtained or side effects occur. Drowsiness is the most common side effect, but patients may also experience nausea, vertigo and unsteadiness. Propranolol, a beta-blocker, is usually effective between 240 and 320 mg daily.9 Patients are frequently referred to movement disorders centers and labeled as having "failed" propranolol treatment, when in fact, an adequate close was never administered. As with primidone, propranolol should be started at low doses and increased over weeks, while monitoring blood pressure and pulse. Contraindications for the use of propranolol include cardiac conduction block, heart failure, asthma and diabetes; side effects include lightheadedness, fatigue, nausea and depression.
Other medications for ET are generally not proven to be as effective as primidone or propranolol, though topiramate was recently shown to reduce tremor in a double-blind, placebo-controlled trial.10 Benzodiazepines such as alprazolam or clonazepam may also help if the patient has concurrent anxiety.
When the medications fail to control the tremor, surgery should be considered. Stereotactic ablation of the ventral intermediate nucleus (Vim) of the thalamus used to be the preferred surgical procedure for control of ET tremor, but has become obsolete with the advent of deep brain stimulation (DBS) of the thalamus.11 Thalamic DBS involves the placement of an electrode in the Vim nucleus. This electrode is connected to a wire, which is tunneled under the skin and attached to an implantable pulse generator located in the subcutaneous tissue overlying the pectoralis muscle. This pulse generator can then be switched on or off and programmed using a portable computer. The clinical effect of DBS is identical to that of ablation, but DBS holds an advantage over ablation in that turning the stimulator off can reverse its effects. Thalamic stimulation can also be performed bilaterally with fewer side effects than thalamotomy.
PARKINSON'S DISEASE (PD)
PD is a slowly progressive neurodegenerative disorder characterized clinically by the classic triad of rest tremor, bradykinesia and rigidity. Although a fourth feature, postural instability, is sometimes included among the cardinal manifestations, this symptom is often absent until the later stages of disease. The diagnosis of PD is made clinically, based on the presence of two out of the three cardinal features and an unequivocal, sustained response to dopaminergic therapy.' PD is uncommon under the age of 40 and increases rapidly in incidence above the age of 60 for both males and females, with a mean age at diagnosis of 70.5 years.12
Approximately 70% of PD patients will have tremor as the initial symptom."The rest tremor in PD has a frequency of 4-6 Hz and a characteristic "pill-rolling" action when the arm and hands are involved. As mentioned earlier, it is not unusual to see an action or postural tremor with PD, especially in the later stages of disease, although this action component generally has a higher frequency (-1 to 12 Hz). In addition to the arms, PD tremor can also affect the legs, lips, jaw, chin, and tongue, but rarely involves the head, differentiating it from ET. The tremor tends to start intermittently in one arm, but gradually becomes more constant, and generally progresses to the contralateral side a few years into the course of the disease. Similar to ET, factors that exacerbate tremor in PD include anxiety, stress, or emotional states or extremes in temperature.
The treatment of PD remains symptomatic. Although research efforts are focusing on neuroprotective strategies and treatment, there are no therapies that unequivocally slow the progression of PD. Therefore, if the patient's symptoms are not limiting, treatment does not need to be initiated. Nevertheless, most patients with prominent rest tremor will opt for treatment because the tremor is annoying or embarrassing. Unfortunately, the response of parkinsonian tremor to pharmacologie treatment is highly variable.1
As a general rule, if the patient is young (
When the patient presents with PD symptoms at a more advanced age (>70 years of age), carbidopa/levodopa is a more appropriate choice. Carbidopa/ levodopa comes in both standard and controlled release formulations, but patients tend to respond less predictably to the controlled release formulation. It is reasonable to begin with the 25/100 mg dose of carbidopa/levodopa two to three times a day, and then increase the dosage as needed for the patient to function independently.
The anticholinergic trihexyphenidyl hydrochloride (Arcane) can improve tremor in PD, but is ineffective in controlling the other cardinal motor features of PD. Therefore, its use is limited to the PD patient who presents with a predominant tremor, but minimal bradykinesia and rigidity, or as adjunctive therapy for a tremor that is resistant to the dopaminergic medications mentioned earlier. Sedation is the main side effect in addition to anticholinergic symptoms such as blurred vision, dry mouth and urinary retention, and is usually the limiting factor in the use of this agent. Trihexyphenidyl should also be used cautiously in elderly patients because they are more prone to developing cognitive difficulties. Dosages needed to suppress tremor can range from 2 to 12 mg daily (maximum dosage 32 mg); again, it is wise to start at a low dose and titrate up for effect. If trihexyphenidyl is ineffective or poorly tolerated, propranolol (lnderal) or amantadine hydrochloride (Symmetrel) can be tried.
If the tremor is refractory to pharmacologie modalities, DBS should be considered. The three anatomical sites in which stimulation has been studied for PD include the thalamus, globus pallidus interna (GPi) and the subthalamic nucleus (STN). Thalamic stimulation is effective only for tremor, and therefore is helpful for only a small proportion of PD patients. Both GPi and STN stimulation have been shown to improve all cardinal features of PD, including tremor,17 and either would be an appropriate option for the majority of patients.
CEREBELLAR TREMOR
Cerebellar tremor most often presents as a kinetic tremor with a prominent intention component.5 The ipsilateral arm or leg is usually affected when a cerebcllar hemisphere in involved. Lesions of the cerebellar vermis, or midline, often cause an isolated postural tremor of the trunk and head, commonly referred to as "titubation". Multiple sclerosis (MS) is the most common cause; other causes include tumors, ischemie or hemorrhagic strokes, alcoholic cerebellar degeneration, vitamin E deficiency, or paraneoplastic syndromes. Treatment of the underlying cause (i.e. immunomodulatory therapy in MS, resection of a tumor) can sometimes resolve the tremor. For persistent cerebellar tremor, however, no medication has been proven to be helpful. A sensible approach is first to try the agents that are helpful for ET. If these fail to relieve the tremor, isoniazid or DBS can be considered. Isoniay.id resulted in mild improvement in one small randomized crossover trial of six patients with severe postural cerebellar tremor,18 while thalamic DBS showed some benefit for cerebellar tremor in a small number of patients with MS.19
PSYCHOGENIC TREMOR
Although there are no precise estimates of the incidence and prevalence of psychogenic tremors, clinical experience suggests that it is not rare. While it can be difficult to differentiate between psychogenic and organic tremors, the characteristic that all psychogenic tremors have in common is variability in the tremor amplitude and frequency.2 Because of this variability, the tremor often cannot be easily classified. Psychogenic tremors frequently increase in severity with attention, and decrease when the patient is forced to concentrate on other tasks. Other criteria useful in the diagnosis of this tremor include sudden or abrupt onset, variable course with spontaneous remissions, ability to perform some functions despite severe tremors, and unresponsiveness to anti-tremor medications.20 Often, "false" signs will appear on the neurologic examination, such as give-way weakness or bizarre sensory findings. Psychotherapy is the main treatment approach.
SUMMARY
Tremor is a common and disabling symptom that is associated with a large number of neurological disorders, including ET and PD. The positional properties of the tremor allow the clinician to generate a short list of diagnostic possibilities, which can then be narrowed down based on the clinical history and the neurological examination. A number of medical and surgical therapies are available for tremor, but a successful response to treatment depends on an accurate diagnosis.
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KELVIN L. CHOU, MD
Kelvin L. Chou, MD, is a Movement Disorders Fellow at the Parkinsons Disease and Movement Disorders Center, Pennsylvania Hospital, University of Pennsylvania School of Medicine, and will be joining the Department of Clinical Neurosciences at Brown Medical School as an Assistant Professor of Neurology in july.
CORRESPONDENCE:
Kelvin L. Chou, MD
Parkinson's Disease and Movement
Disorders Center
330 South Ninth Street
Philadelphia, PA 19107
Phone: (215) 829-8593
Fax: (215) 829-7552
e-mail: chouk@uphs.upenn.edu
Copyright Rhode Island Medical Society May 2004
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