Essential Tremor

Trembling
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Diagnosis and reasoning

Tremors are the most common movement disorder encountered in clinical practice; the range of causative pathologies is wide, including both benign and not-so-benign lesions. A careful history and examination is key in these patients; in many cases, this alone will establish the diagnosis. The first step should be to classify the tremor as either resting or actional; the tremor in this patient falls into the latter category. Action tremors can in turn be subdivided into postural tremors (i.e. when the body part is maintained against gravity), kinetic tremors (i.e. occurring with any form of movement), and intention tremors (where the tremor is amplified as the target is reached). Note that the tremor in this patient can be classified as 'postural'. The main conditions giving rise to a postural tremor include essential tremor (ET), enhanced physiologic tremor (EPT), cerebellar tremor, and drug-induced tremors. The absence of drug therapy excludes the last of the above; note also that cerebellar tremors are usually of a low frequency (3 to 4 Hz), and that there are no cerebellar signs in this patient. This leaves ET and EPT as the likely candidates; however, note that EPT rarely results in severe functional impairment (as in this patient). Nevertheless, she should be screened for potential endocrine and metabolic diseases which can give rise to EPT (particularly hyperthyroidism, liver disease and renal disease). However all tests are normal in this regard. Thus, the diagnosis is ET indeed; therapy with a beta-blocker (such has propranolol) should be commenced. Gamma knife radiosurgery should be reserved for patients with severe ET unresponsive to conservative measures. Note that Levodopa is used in the treatment of Parkinson's disease; Lithium may cause tremors and has no role in the management of this patient.


Discussion

Essential tremor (ET) is the most common movement disorder, with an estimated prevalence of up to 5% of the worldwide population. The condition is familial in around 50% to 70% of cases, with an autosomal dominant pattern of inheritance. ET typically manifests as a bilateral, symmetrical tremor which is most often postural, but which can also be intentional, and involving the hands and forearms. Almost one-third of these patients may also demonstrate involvement of the head and neck. The head is affected most often, followed by the larynx, jaw, and face. Note that ethanol intake temporarily reduces tremor amplitude in 50% to 70% of patients. ET is mainly a clinical diagnosis, based on the features listed above; however, note that it is prudent to exclude organic conditions which may mimic this presentation (such as hyperthyroidism, liver disease, renal disease, and in young patients, Wilson disease). Note that while quantitative computerized analysis of tremors is available in some tertiary care centres, its ability to reliably distinguish between the various types of tremor has not been established. ET can be managed either medically or surgically; propranolol and primidone are the cornerstones of maintenance medical therapy in these patients. Surgery is indicated in patients with disabling, medically refractory tremors; surgical options include thalamotomy and thalamic deep brain stimulation. Conventional thalamotomy can be performed using stereotactic surgical techniques; the more modern gamma knife thalamotomy uses targeted radiation instead. In deep brain stimulation, electrodes are implanted in the thalamic ventral intermediate nucleus using stereotactic methods. While ET is a benign condition, there is a significant incidence of disability in these individuals. The majority report significant changes in their livelihood and socialising, and about 15% report being seriously disabled by the condition.


Take home messages

  1. Essential tremor (ET) is the most common movement disorder; it is often familial in nature.
  2. ET is a clinical diagnosis.
  3. Therapy with beta-blockers is the first line treatment in these patients.

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