Incidence and subtypes of early-onset dementia in a geographically defined general population.

OBJECTIVE: To estimate the incidence of early-onset dementia (EOD) and to compare the clinical characteristics of EOD vs late-onset dementia (LOD) in a geographically defined area. METHODS: We used data from the Registry of Dementia of Girona (ReDeGi), an epidemiologic surveillance system of dementia. The ReDeGi is a standardized clinical registry of new dementia cases diagnosed in the 7 hospitals of the Health Region of Girona (Catalonia, Spain), which encompasses an area of 5,517 km(2) and 690,207 inhabitants. EOD cases were defined as those patients residing in the target area at the time of diagnosis who were diagnosed with dementia with an age at onset of symptoms before 65 years. RESULTS: The ReDeGi registered 2,083 patients between January 1, 2007, and December 31, 2009 (6.9% EOD). The incidence rate of EOD for the age range 30-64 was 13.4 cases per 100,000 person-years (95% confidence interval 11.3-15.8). Alzheimer disease was the most frequent cause of EOD (42.4%), followed by secondary dementia (18.1%), vascular dementia (13.8%), and frontotemporal dementia (9.7%). EOD cases at the time of diagnosis were less impaired on the Mini-Mental State Examination and had a greater score on the Blessed Dementia Rating Scale behavior subscale than LOD cases. The frequency of a personal history of depression was higher in EOD cases. CONCLUSIONS: The incidence of EOD was less than 6 cases per 100,000 person-years in the age group 30-49 years; in the age group 50-64 years, the incidence rate was 3-fold higher and doubled with each 5-year increase.