Essential Tremor (ET) - Clinical Diagnosis

Essential Tremor

Clinical Diagnosis

Because no diagnostic pathologic findings or biologic markers are available, correct diagnosis often depends on the clinician's skill in recognizing the clinical features of ET. Although there are no universally accepted criteria for ET, classification schema, such as the NIH Collaborative Genetic Criteria, the TRIG Criteria, and the Consensus Statement of the MDS on Tremor, provide a framework for the definition of inclusion and exclusion criteria for ET. (Please refer to "Clinical Classification of Tremors.")

In patients with tremor, diagnostic evaluation begins with a thorough medical and historical evaluation to determine...

Presence of a positive family history
Age of onset
Anatomical distribution, type, and severity of tremor
Presence of abrupt tremor onset or concomitant neurologic disease that may suggest an alternative diagnosis
Administration of pharmaceutical agents or exposure to toxins that may induce tremor
Effect of ethanol on tremor symptoms. (Consuming even small quantities of alcohol leads to transient improvement of tremor in many ET patients. However, only rarely may other tremor patients, such as those with PD, experience such an alleviation of symptoms.)

Physical examination
Tremor patients should receive a thorough neurologic examination. To properly distinguish between resting and action tremors, patients should be evaluated while supine and when seated with the arms fully supported. (If patients are seated in a position that does not provide complete support, certain muscles may be active against gravity, producing a tremor that may be improperly classified as a resting tremor.) In addition, it is important to encourage patients to describe their tremors in detail.

During a thorough tremor-focused neurologic examination...

Muscle tone is checked throughout the body.
Cranial structures (including the mouth and jaw) are examined at rest and in action.
The tongue is observed during rest and protrusion.
The upper extremities are examined while the patient is seated with the arms fully supported.
The upper extremities are examined in an outstretched position with the hands supine (palms up), prone (palms down), and in the wing position (i.e., with apposition of the index fingers close to each other but not touching).
Goal-directed activities are performed, such as finger-to-nose, heel-to-shin, and toe-to-finger movements. In addition, the patient may be evaluated while pouring water from one cup into another.
The patient is asked to recite a standard paragraph and enunciate a sustained vowel.
Handwriting samples are obtained (e.g., script, numbers, Archimedes spirals).
Gait is evaluated and Romberg (station) and balance testing are conducted.
Careful evaluation is performed for signs of other neurologic disease, including PD and dystonia.

Tremor assessment
Although no single test is pathognomonic for ET, several tools are available to help evaluate the condition. These include a tremor assessment form that may assist in differential diagnosis, and provide information regarding tremor severity and progression. Other methods used to measure tremor include physical examination (refer to "Physical examination"), physiologic techniques, subjective clinical measures, objective functional performance tests, and assessment of the impact of tremor on patients' lives.

Physiologic techniques are used to obtain objective measures of tremor magnitude and frequency. These may include linear accelerometric studies, short-term or long-term EMG, and graphic digitizing tables for the measurement of tremor during drawing and writing. Also available are gyroscopic techniques that sense trunk and limb rotation rate and computer tracking tasks that measure the error resulting from tremor during performance of manual tasks. In addition, mechanical and optically based systems create digital coordinates of the movement of light-emitting or infrared diodes attached to the patient. When compared to simpler clinical measures, such techniques are generally expensive and time-consuming and typically are not available in the clinician's office.
Subjective clinical measures of tremor include clinical rating scales and rating handwriting or spiral drawings, known as Archimedes spirals. ET patients typically have handwriting that is shaky and large, whereas that of PD patients may initially be of normal size and progressively become smaller (micrographia). Archimedes spirals drawn by ET patients tend to illustrate natural fluctuations in tremor magnitude.
Objective functional performance tests tend to be inexpensive, are simple to use, and objectively evaluate the performance of actions involved in real-life activities. Such tests may include measuring the amount of water spilled while pouring water from one cup to another or holding a cup for 1 minute; the 9-hole pegboard test; or maze tests, such as assessment of the number of times a patient's drawn line crosses the boundaries of a preprinted spiral.
Assessment on the impact of tremor on patients' lives includes measures of disability, handicap, and QOL. Functional disability is a measure of the difficulty encountered in performing ADLs, whereas resultant handicap is often described as the consequence of having certain disabilities. QOL is typically viewed as a patient's subjective assessment of his or her state of affairs. Such measures may be quantified using generic or disease-specific questionnaires.

Other investigations
Laboratory testing may be necessary to exclude certain conditions that may be associated with tremor, such as metabolic disturbances, including hyperthyroidism (e.g., through thyroid function tests); Wilson's disease, as suggested by reduced serum ceruloplasmin levels; etc. In addition, neuroimaging studies, such as computerized tomography (CT), magnetic resonance imaging (MRI), or PET scanning, may also be required for selected patients, particularly those with tremor that is unilateral, of sudden onset, or associated with atypical clinical features.

Documentation
To objectively evaluate disease progression and patient response to treatment, it is necessary to thoroughly document tremor severity as assessed above. Documentation should also include specific details concerning the anatomic regions affected; specific tremor type(s) present (e.g., postural, kinetic, etc.); and assessment of the impact of functional disability and resultant handicap on ADLs and QOL.