Revisiting the assessment of tremor: clinical review

History

Characterising the onset age, anatomical distribution (head, voice, hands, and symmetry), and temporal evolution of the tremor is important, forms the first step of the assessment, and aids in determining the underlying syndrome (outlined in subsequent sections). A key aspect to establish early is if the tremor results in functional impairment as this will determine if treatment is warranted (all current treatment options are symptomatic, that is, non-disease modifying).^7,8 Useful questions to establish this include when the tremor is worst (writing, using a cup, relaxing) and whether assistance is needed, for example, with preparing food. Then, relevant family and past histories (medication exposure, alcohol, and drug sensitivity) as well as the presence of other neurological symptoms (for example, slowing up, gait disturbance, muscle stiffness, and aches) should be explored. The latter aspects are more typical of PD than ET and can provide early diagnostic clues in differentiating these two conditions. Some tremorgenic medications to consider include salbutamol, ciclosporin, haloperidol, lithium, and valproic acid. Caffeine intake, anxiety, and alcohol use can result in or exacerbate pre-existing tremor and these aspects should be clarified on history taking. However, some forms of tremor are alcohol responsive so alcohol misuse may be secondary to an underlying neurological condition.

Examination

Observation is key and should continue throughout the consultation. This includes the patient’s gait and movements when walking into the room, particularly noting how easily they stand up (difficulty in parkinsonian syndromes), how far apart their feet are (broad stance implicates potential proprioceptive or cerebellar impairment), and if they take appropriately spaced strides (short strides in parkinsonian syndromes). Other parkinsonian features (reduced blinking, decreased facial expression, stooped posture), the location of the tremor, and the presence of systemic signs (exophthalmos, goitre) may also be evident before the formal examination.

Defining tremor characteristics (frequency, amplitude, and nature) is of little value though establishing changes in activation conditions is useful. This includes assessments at rest — limbs supported on the patient’s lap (Figure 1A) and observing for tremor with distraction (counting backwards or complex subtractions), which is typical of PD tremor. Postural tremor is then assessed with both upper limbs outstretched (Figure 1B) and followed by the finger–nose task (Figure 1E), looking for a kinetic or intention tremor. During the transition from rest to posture, re-emergent tremor (that is, the tremor disappears and then reappears) should be established (strongly suggestive of PD). Additional movements (dystonia or myoclonus) should also be noted. Definitions are outlined in Box 1.

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Figure 1.

Physical examination of tremor.^a

^aThe tremor is first assessed at rest, palm up with upper-limb support on the patient’s lap (A). A postural tremor is then searched for by asking the patient to outstretch their arms (B). A bradykinesia, suggestive of an extrapyramidal syndrome, can be identified by asking the patient to tap the finger (C and D). Eventually, an intention tremor is better shown by the nose–finger test (E).

Coexistent limb parkinsonism can be detected with finger taps (Figure 1C, D). Patients tap their thumb and index finger approximately 10 times. Small and slow movements suggest bradykinesia whereas taps progressively becoming smaller (decrement) or stopping imply PD. Rotation of the hand at the wrist to note for resistance (extrapyramidal tone) follows. Handwriting to assess for micrographia (small handwriting, progressively gets smaller) or writing tremor and functional impairment (for example, pouring water from cup to cup) completes the examination. Exacerbation (or provocation) of tremor when pouring water from cup to cup is typical of essential and dystonic tremor.

Investigations

Tests to exclude symptomatic causes (thyroid, renal, and liver function) should be performed in primary care. Additional tests may be pertinent but should be considered by specialists.

Essential tremor

Essential tremor is an isolated bilateral upper-limb action tremor syndrome. Although coexistent tremor (head, voice, lower limbs) can occur, isolated tremor in these regions should not be regarded as ET.⁵ Useful diagnostic features include tremor during action, including writing, holding a cup and saucer and pouring, together with the absence of bradykinesia. A 3-year observation period during which the tremor is considered indeterminate has been proposed. This is to safeguard against the development of additional features and therefore alternative syndromes. If the onset is sudden and deterioration stepwise this should prompt clinicians away from ET. Although responses to alcohol, propranolol, and a family history are sometimes evident, these are not reliable diagnostic features.⁵ The presence of other neurological signs, even if subtle or uncertain, constitute the new entity essential tremor plus (ET-plus)⁵ and warrant neurological input.

Essential tremor plus

Patients with ET-plus have ET features with additional signs that are subtle and their presence at times questionable. Dystonia is the most common of these and may include minimal flexion posturing of the fingers/wrist or pronation/supination tilting of the outstretched hands. This group either represent novel disorders or alternative conditions (dystonic tremor, PD) in their infancy. Although diagnostic value is currently lacking, practitioners are encouraged to attempt characterisations and consider referral as it could potentially alter future outcomes.

Enhanced physiological tremor

Enhanced physiological tremor (EPT) resembles ET and occurs because of an enhancement of normal physiology by precipitating conditions (anxiety, drugs, and thyroid disease).⁹ EPT tends to vary with these factors and is not functionally limiting. The proposed 3-year ET observation period potentially aids in delineation and reversal of causes.

Tremor combined with parkinsonism

Classical parkinsonian tremor manifests with a 4–7 Hz asymmetrical hand tremor, resting ‘pill-rolling’ tremor with associated bradykinesia (with decrement), and rigidity. Lower-limb, jaw, tongue, or foot tremors can variably coexist.⁵ Postural/kinetic (action) tremor resembling ET can be a presenting feature of PD. These patients should therefore be regularly re-examined for emergence of Parkinsonism. PD tremor usually abates with action or assuming a position, with re-emergence with sustained posture (re-emergent tremor).¹⁰

Isolated focal tremors

Focal tremors affect the head, voice, palate, or limbs and occur in isolated conditions or during specific tasks such as writing or while playing instruments or sport.^11–13 These tremors potentially reflect underlying dystonia and should not be regarded as ET.^5,14 They can at times be attributed to an underlying lesion^14,15 or suggest a genetic abnormality.¹⁶

Isolated rest tremor without parkinsonism should either prompt careful clinical surveillance or imaging for dopaminergic deficiency.¹⁷ If rest tremor occurs in conjunction with an ET phenotype (typically in advanced stages) and in the absence of parkinsonism, this constitutes ET-plus.⁵ Neurophysiological assessments can aid in distinguishing PD from ET rest tremor.¹⁸ Orthostatic tremor (OT) is an isolated tremor occurring mainly in patients’ lower limbs when standing. Although coexistent upper-limb or head tremors can occur,^19,20 this should not be regarded as ET. Diagnostic delays have been noted¹⁹ as initial symptoms can be non-specific (legs feeling like jelly, unsteadiness). These features should therefore prompt a clinical suspicion for OT.

Dystonic tremor syndromes

If a tremor occurs in a body part affected by dystonia this is termed dystonic tremor (DT). Tremor and dystonia occurring in different body regions in contrast are defined as tremor associated with dystonia.^5,21 DTs are typically variable, and are jerky.²¹ Other distinguishing signs exist²¹ though detection would not be expected in general practice. The distinction between DT and ET-plus with dystonia currently solely relies on the confidence of a clinician in apportioning dystonia though neurophysiology may change this in the future. Patients with DT can present with an isolated head tremor and/or associated head and neck posturing (cervical dystonia). This can occur in isolation or in combination with an asymmetrical upper-limb tremor. DT’s variable nature can sometimes lead to a misdiagnosis of a functional tremor. Specialist input should therefore be sought in these cases nor only to clarify first the diagnosis but also for consideration of specific efficacious treatments such as botulinum toxin therapy or functional neurosurgery.

Intention tremor syndromes

Previously classified as cerebellar tremor, these cases are now considered as either isolated or combined (typically dystonia or cerebellar signs) intention tremor syndromes. Intention tremors are typically <5 Hz with an underlying cause in the brainstem-cerebello-thalamic pathway.⁵

Functional tremor

Functional tremor is diagnosed with the demonstration of ‘positive’ features (sudden onset and inconsistencies, fluctuations, distractibility, and entrainability on examination). Although a coexisting psychiatric history in particular anxiety can be present, it should not be relied upon.²² Neurophysiology can sometimes aid the diagnosis,²³ which should be established by a specialist.