Time trend in diagnosing dementia in secondary care.

Background: To study the trend of diagnosing dementia in the secondary health care sector over time, we conducted a nationwide longitudinal study of the incidence and prevalence of registered dementia diagnoses in the Danish national hospital registers.

Methods: All Danish residents born before 1964 and alive at their 40th birthday were followed from their 40th birthday or January 1, 1970, whichever came later, to the date of the first dementia diagnosis recorded in the hospital registers, the date of emigration, date of death, or December 31, 2004, whichever came first. The age- and period-specific incidence and prevalence of dementia were calculated and compared to estimates from large community-based cohort studies in Europe.

Results: The study population consisted of 4,723,838 persons with 81,090,583 person-years of follow-up. 154,152 dementia cases were registered from 1970 to 2004. The incidence and prevalence of registered dementia diagnoses showed an increasing trend over time. In 2003, the age-standardized incidence rate ratio was 0.66 when compared to estimates from large European community-based cohort studies.

Conclusions: The study shows a marked improvement in the diagnostic rate of dementia in secondary care over time and indicates that this sector can be an important point of entry for patients with dementia.