Essential Tremor - Is There a New Nosological Concept?

Essential tremor (ET), the most common form of pathological tremor, affects up to 4% of the population. According to the traditional concept, ET is a monosymptomatic benign clinical entity where tremor is associated with longevity and positive family history. Despite the high prevalence and suspected genetic component, research failed so far to find a causative gene mutation for ET. The main reason is probably related to an imperfectly bounded nosological concept. There are still uncertainties around clinical definition of ET, which does not include isolated head tremor, voice tremor or task-specific tremors that often overlap with dystonic tremor. Moreover, numerous studies have shown the incidence of parkinsonism, cerebellar signs and cognitive disorders in ET. Age of onset turns out as a key factor, characterized by two peaks in the adolescence and in the old age. The classical concept of ET corresponds to early onset disease characterized by a positive family history, more benign progression, and relief after alcohol. Conversely, so called aging-related tremor is usually characterized by late-onset, sporadic occurrence, rapid progression, and also by cognitive dysfunction and other symptoms and signs suggestive of neurodegenerative disorder. Thus, rather than a monosymptomatic nosological entity, ET appears as a group of diseases featuring action tremor. Besides unclear etiology, the possible contribution of neurodegenerative processes remains an open question in the pathogenesis of ET. Thereafter, a thorough description of the individual phenotype along with the methods of genome-wide association studies can contribute to finding causal gene polymorphisms in ET and to elucidate the pathogenesis of various forms of the disease.