Tremor: a simple four-step approach to clinical assessment

Tremor is the most common movement disorder encountered in clinical practice.1-3 It is defined as an involuntary, rhythmic and oscillatory movement of a body part. Tremors tend to be relatively constant in frequency but variable in amplitude,1 which may happen due to exaggeration of the physiological tremor or due to a tremor disorder. If significant enough, it may lead to medical presentation.

The most common tremors encountered in clinical practice in order are:3

• Physiologic tremor. All persons have tremors at rest3 and, particularly, with posture, as these require continuous adjustments of agonist and antagonist muscles to prevent the limb from moving. These alternating or synchronous contractions of antagonistic muscles may become significant enough to be noticeable in healthy patients. They are increased by adrenergic and serotonergic activity, including caffeine use, anxiety or excitement, pyrexia, thyrotoxicosis and alcohol withdrawal.

• Essential tremor (ET). ET has an estimated 5% population prevalence,1 the incidence of which increases with age. A family history is present in about half of the patients,3 typically an autosomal dominant pattern of inheritance with reduced penetrance.

• Parkinson disease (PD) tremor. This is the main differential that patients will be concerned about, given its relative frequency and implications for progressive disability. A small proportion of PD cases are familial. Tremor is the presenting complaint in 70% of patients with PD.3

• Functional or psychogenic tremor. This type of tremor occurs in 10% of specialist clinic presentations;2 it tends to present as bizarre or incongruent tremor and accompanying features.

• Cerebellar tremor. These tremors are commonly caused by medications or structural lesions.2

• Dystonic tremor. This tremor is defined as tremor in association with abnormal posturing.2 It occurs in 0.03% of the population, usually under the age of 50 years, and is jerky and irregular.3

Assessment of tremor includes history and examination. Investigations are often less useful, as they will typically be normal in the most common forms of tremor. Laboratory studies for thyroid function should be performed in all patients with tremor because hyperthyroidism may exacerbate any tremor type. Tests for Wilson disease should be considered in patients under 40 years of age with any involuntary movement or posture.1 Brain imaging can be useful in patients suspected clinically of having a structural cause for tremor, but is otherwise usually not indicated. Dopamine transporter single-photon emission computed tomography scans correctly classify 97.5% of PD tremor and 100% of ET4 cases, but is not routinely available in Australia. Computed analysis of tremor with surface electromyography has limited availability, and its utility has not been proven.

The following is a useful four-step clinical approach to the evaluation of a patient with tremor. Once the symptoms and signs have been determined, the Box can be used to try to classify the type of tremor and the disease association.

Activation state

Activation state is often the most diagnostic feature of the phenomenology of the tremor (Box) and is divided into resting or action:3

• resting tremor — in body parts completely supported against gravity and relaxed; and

• action — which is further divided into postural, kinetic and intention tremor:3

  • postural tremor occurs when the joint is held in a static position but working against gravity;

  • kinetic tremor occurs during voluntary muscle activation; and

  • intention tremor occurs during target-directed movement.

   

History involves enquiring about the position where the tremor is most noticeable and about factors that may affect it. Ask the patient if the tremor is present with arms relaxed watching television, and enquire about the effect of caffeine, alcohol and family history. ET is typically relieved by small amounts of alcohol, but, in contrast with physiologic tremor, is not usually aggravated by caffeine.

Examination of activation state should commence with the patient as relaxed as possible, preferably lying on the examination couch. Next, mental distraction techniques should be used (eg, counting backwards out loud from 100), which will often increase a resting tremor. For postural assessment, have the patient extend their arms, note whether the tremor abates as the arms extend and if the tremor returns and its severity with arms extended. For kinetic tremor, observe the patient during the finger–nose–finger test, and whether the tremor worsens towards the end of this goal-directed movement (intention). Observe the patient holding a glass of water, and lastly, draw a spiral.

Distribution

The distribution refers to the body part affected, which is divided into arms, head and legs. History and examination simply involves inquiring about and looking for tremor in each of these body parts. Patients are often less aware of head tremor than relatives or physicians.

Frequency

The frequency is often divided into low (< 5 Hz), medium (5–7 Hz) or fast (> 7 Hz),3 and is often quite difficult to count accurately.

Accompanying features

The accompanying features are often the most useful disease association feature (Box), helping distinguish isolated tremor disorders from disease process and then further subclassifying disease processes.

Assess both by history and examination involvement of soft voice, facial expression and postural hypotension. Bradykinesia of hand movements is assessed with arms in near full extension, shooting fingers in and out rapidly, “playing the piano” and tapping index finger to thumb repetitively attempting to keep the amplitude and rate high. In the bradykinesia of PD there will be progressive reduction of amplitude. In particular, observe the gait pattern — narrow based, short and low steps — but reduction of upper arm swing in the tremulous arm is strongly suggestive of PD. Once the clinical assessment is complete, the Box is helpful in tremor classification.