12 Essential Tremor: Evaluation, Imaging and Medical Treatment
Abstract
Essential tremor (ET) is a common movement disorder characterized by postural and action tremors of the hands, head and voice, often with a family history, that tends to improve with alcohol and worsens with stress or anxiety. It can typically be distinguished from other tremor types, including parkinsonian, dystonic, neuropathic, and drug-induced tremors. Symptoms are often symmetric and clinical progression is typically slow. The pathophysiology is thought to be mediated by abnormal output activity in the cerebello-thalamo-cortical pathways, and is supported by post-mortem and imaging studies. Medical treatments for ET include propranolol and primidone (amongst others) and may require polypharmacy in advanced cases.
12.1 Introduction
Essential Tremor (ET) is one of the most common movement disorders with an estimated prevalence of 0.4%-3.9% with an even higher prevalence of 4.6% in those older than 65. 1 , 2 This disorder has a bimodal distribution of age at onset with a small peak in those individuals in their second and third decade with a larger incidence in individuals in their seventh and eight decades. 3
12.1.1 Phenomenology and Family History
Essential Tremor is defined as a typically hereditary and predominantly postural and kinetic tremor syndrome affecting the hands. Tremor of other body parts (e.g., the head, voice and trunk) may also be present. 4 The characteristic 4–12 Hz postural tremor is typically bilateral and largely symmetric. 4 , 5 Approximately 60–70% of patients report improvement with alcohol, while anxiety, stress, and caffeine worsen tremor. 5 Half of ET patients have a family history, especially those with onset earlier in life. 6 Younger-onset ET patients perform similar to unaffected peers in education and working life while the older-onset patients may have dementia and increased mortality, though neither differs significantly in their level of response to oral medications. 6 A specific disease-causing gene(s) has not been identified.
12.1.2 Rating Scales
Symptom severity can be assessed in the research and clinical settings using clinical scales such as the Fahn-Tolosa-Marin Tremor Rating Scale (TRS) and the Tremor Research Group Essential Tremor Rating Assessment Scale (TETRAS). The TRS is a 5-point (0–4) scale with a maximum total score of 144 7 while the TETRAS was developed more recently and has a maximum score of 64. 8 Both clinical scales include assessment of tremor amplitude in different positions and tasks along with impact on activities of daily living.
12.1.3 Clinical Progression
Progression of ET is slow, especially earlier in the disease process. Patients with younger onset and family history may experience symptoms for over 40 years. 9 One study found four factors that significantly correlated with increased baseline tremor score: older age at first clinic visit, longer disease duration, use of drugs for movement disorders, and the presence of voice tremor. Three factors significantly correlated with faster tremor progression: unilateral or head or neck tremor at onset, asymmetrical disease, and longer duration between baseline and previous follow-up. In this study, the TRS score increased by less than 1 point per year prior to the first clinic visit and approximately 2 points per year during the observed study period (mean follow-up = 3.6 years). 10
12.1.4 Differential Diagnosis
Differentiating tremor syndromes can be difficult given the overlap of rest, postural, and kinetic tremors in tremor disorders. Specific types of tremor are required for diagnosis of their tremor syndrome while other tremors are allowed for diagnosis (▶ Table 12.1). For instance, while action tremor is typically associated with ET and rest tremor with Parkinson’s disease (PD), rest tremor can be seen in up to 30% of ET, but tends to occur in later, more severe stages, and does not exclude the ET diagnosis. 11
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