Does age of onset in essential tremor have a bimodal distribution? Data from a tertiary referral setting and a population-based study.

BACKGROUND/AIMS: The distribution of age of onset of essential tremor (ET) is unclear, with discrepancies in the literature. Some data suggest a bimodal distribution and other data 1 late-life peak. We studied age of ET onset in 2 distinct settings: a population-based study and a tertiary referral center.

METHODS: Age of onset data were collected.

RESULTS: In the population, there was only a small peak at the age of <or=30 years (14.1% of cases) but a clear peak in later life (85.9% of cases). In the tertiary referral center, a bimodal distribution was apparent with 1 large peak (42.2% of cases) at the age of <or=40 years and the second large peak (57.8% of cases) in later life. Familial cases accounted for only 52.6% of young-onset cases from the population, yet 82.7% from the tertiary center.

DISCUSSION: In the population-based study, a peak in later life was clearly present but a young-onset peak was barely discernable, comprising few cases. By contrast, in a tertiary referral center, age of onset was clearly bimodal. While age of ET onset is often said to be bimodal, this may be due to the preferential referral to tertiary centers of patients with young-onset, familial ET.