Essential Tremor: From a Monosymptomatic Disorder to a More Complex Entity

Fertility rate is the number of children born per couple, person or population. In this issue of Neuroepidemiology, the article by Louis [18] examined whether ET cases and controls differed in terms of number of children. To do so, cases and controls were sampled from two distinct settings, a population and a clinical referral sample. This author has shown that the proportion of ET cases and controls with offspring was similar and the number of offspring was similar in ET cases and controls. The relevance of this study is to have shown that there is no increased fertility in ET, further refuting the idea of ET as a super-healthy condition. Taken together, all of these recent data support the view that ET is not an innocuous condition. As in other progressive, late-life neurological diseases, further mechanistic research on ET must be pursued. A better understanding of the anatomical and pathological bases of this disease will lead to advances in better symptomatic treatments, and also possibly neuroprotective therapies. Essential tremor (ET) is one of the most common neurological disorders among adults, and it is the most common tremor disorder [1, 2] . For many years, ET was viewed as a monosymptomatic condition, characterized by a kinetic arm tremor, yet over the last 10 years, a panoply of previously unrecognized motor and nonmotor problems has emerged [3–10] . The new paradigm presents ET as a more complex clinical entity [2] . In addition, emerging pathological studies are providing evidence that ET is likely to be a neurodegenerative disease [11–13] . These studies demonstrate Purkinje cell loss and other degenerative changes in the cerebellum of the majority of ET cases and Lewy bodies in the brainstem of the remaining cases [11–13] . As with other progressive neurological disorders of later life (e.g. motor neuron disease and Parkinson’s disease), ET might represent a family of related diseases that show heterogeneity at etiological, clinical and pathological levels [2] . In contrast to the view of ET as progressive and degenerative, there is an older view that ET is a benign and even possibly a ‘super-healthy’ condition. Thus, in the 1920s, the Russian neurologist Minor [14] proposed an association between familial tremor, longevity, and fertility and called it status macrobioticus multiparus . Although most researchers have not accepted this association, some modern studies have further propagated this notion of ET as benign or super-healthy by suggesting an association between tremor and longevity [15] . Yet nowadays, the weight of emerging evidence is showing that ET is not a benign or superhealthy condition. It is in fact associated with gait disturbances [3] , personality changes [4] , low morale [5] , depressive symptoms [6] , hearing impairment [7] , cognitive deficits [8] , and dementia [9] . Perhaps, the most important result in recent years has been the demonstration that elderly-onset ET represents a condition of poor prognosis, particularly in terms of increased risk of both dementia [10] and Parkinson’s disease [16] , and increased risk of mortality [17] . Published online: September 11, 2008