Dementia incidence trends in rural Spain: Ten-year cohort findings from NEDICES cohort.

PURPOSE: To estimate dementia incidence in the rural population enrolled in the Neurological Diseases in Central Spain (NEDICES) cohort and to evaluate the impact of ascertainment strategies on temporal trend estimates.

METHODS

Residents aged ≥65 years were examined at baseline (1994-1995), in 1997-1998, and in 2004-2005. Incident dementia was identified through clinical reassessment, medical record review, and, for decedents between waves, via linkage to the Spanish National Death Registry. Person-time accrued from baseline to dementia, death, or censoring; incidence rates (per 1000 person-years) with 95% confidence intervals (CIs) were estimated using exact Poisson methods; incidence rate ratios (IRRs) contrasted 1994-1998 with 1999-2005.

FINDINGS: Of 2148 eligible residents in the 1993 census, 1937 were screened; 113 prevalent cases were excluded, leaving 1824 dementia-free participants. In 1994-1998, 60 incident cases occurred over 4427.3 person-years (13.6; 95% CI, 10.5-17.5): 41 detected at first follow-up, 13 reclassified at the third wave, and 6 identified from death certificates. In 1999-2005, 76 cases accrued over 2584.9 person-years (29.4; 95% CI, 23.3-36.9); 23 were actively ascertained, and 53 were registry-only, resulting in an IRR of 2.17 (95% CI, 1.55-3.04; p < 0.001). Restricting to actively ascertained cases, rates were 12.2 versus 8.9 (IRR = 0.73; 95% CI, 0.45-1.19; p = 0.20). Alzheimer's disease was the most frequent subtype.

CONCLUSIONS

The incidence increased only when death certificate diagnoses were included; active follow-up suggested stability. This higher incidence may reflect older age structure, lower educational attainment/cognitive reserve, heavier vascular risk burden, and constrained diagnostic access that shifts detection to death certification.