Essential tremor--a neurodegenerative disorder associated with cognitive defects?

In the past decade, the hypothesis that essential tremor is a monosymptomatic tremorogenic disorder has been questioned. New clinical, neuroimaging, electrophysiological and pathological studies indicate that essential tremor is associated with subtle neurological deficits and could be considered a slowly progressive neurodegenerative disorder. The aim of this Review is to describe the nonmotor neurological symptoms that are commonly associated with essential tremor, and highlight the cognitive deficits associated with this condition. Several clinical studies have demonstrated that essential tremor is associated with mild deficits in attention, executive functions, memory and, possibly, other cognitive processes. Population-based surveys have confirmed that dysfunction in these cognitive domains affects patients both with severe and mild essential tremor. Clinical studies have also indicated that cognitive deficits associated with essential tremor are progressive and that patients with this condition have an increased risk of dementia. Mood and cognitive deficits commonly observed in patients with essential tremor are similar to symptoms of cerebellar cognitive affective syndrome. Further evidence is required from prospective studies to support the interpretation that essential tremor is a slowly progressive neurodegenerative disorder.