Contributed by Leo Verhagen, MD, PhD
Associate Professor of Neurological Sciences
Rush University Medical Center
Chicago, Illinois USA
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Tremor is an unintentional, rhythmic, oscillation of a body part in a fixed plane. Tremor results from contractions of agonist and antagonist muscles entrained by a signal pattern originating from an oscillator in the CNS. Resting tremor occurs in a body part that is not activated and completely supported against gravity. Action tremor refers to tremor occurring with voluntary muscle contraction and is subdivided into postural tremor, isometric tremor and kinetic tremor. The latter is further subdivided into simple kinetic, intention tremor, and task specific tremor, such as writing tremor.
The etiology of tremor is diverse, and includes hereditary, degenerative, and idiopathic disorders such as Wilson’s disease, Parkinson’s disease, and essential tremor, respectively; metabolic diseases (such as thyroid-, parathyroid-, liver disease and hypoglycemia); peripheral neuropathies (associated with Charcot-Marie-Tooth, Roussy-Levy, diabetes mellitus, complex regional pain syndrome); toxins (nicotine, mercury, lead, CO, Manganese, arsenic, toluene); drug-induced (narcoleptics, tricyclics, lithium, cocaine, alcohol, adrenaline, bronchodilators, theophylline, caffeine, steroids, valproate, amiodarone, thyroid hormones, vincristine); and psychogenic disorders.
Clinically tremor can be classified into physiologic tremor, enhanced physiologic tremor, essential tremor syndromes (including classical ET, primary orthostatic tremor, and task- and position-specific tremor), dystonic tremor, parkinsonian tremor, cerebellar tremor (often associated with multiple sclerosis), Holmes’ tremor (a.k.a. rubral tremor), palatal tremor, neuropathic tremor, toxic or drug-induced tremor, and psychogenic tremor.
Contributed by Hubert Fernandez, MD
Head, Movement Disorders
Department of Neurology
Cleveland, Ohio USA
Essential tremor (ET) is the most common tremor syndrome seen in adults. The characteristic tremor seen in ET is postural and action tremors, with a frequency of 4-7 Hz. These tremors may begin insidiously early in life, with an increment in tremor severity over the years. The disability in ET is associated with impairment of voluntary activities that occur as a result of the tremor. Patients commonly complain of tremors when eating, drinking and writing, spilling over food and drinks and developing a progressively illegible handwriting. The most commonly affected body parts include hands, head and voice, but may also be seen in the legs, trunk and face.
Despite being mainly a postural tremor, kinetic tremor may be present and sometimes a resting tremor of lesser severity may be appreciated. The tremor in ET is exacerbated by conditions as stress, exercise and fatigue, caffeine, certain medications and improves with relaxation and alcohol. Several tremor conditions are believed to be variants of essential tremors including: task-position specific tremor (primary writing tremor), isolated voice tremor, isolated chin tremor.
The most common treatments for ET include: primidone, beta blockers such as proporanolol and benzodiazepines. Sometimes, in medication-refractory tremor, deep brain stimulation of the VIM nucleus of the thalamus is considered.