Methodological Factors in Determining Risk of Dementia After Transient Ischemic Attack and Stroke: (II) Effect of Attrition on Follow-Up.

BACKGROUND AND PURPOSE Cognitive outcomes in cohorts and trials are often based only on face-to-face clinic assessment. However, cognitive impairment is strongly associated with increased morbidity and mortality, leading to substantial loss to clinic follow-up. In the absence of previous population-based data, we determined the effect of such attrition on measured risk of dementia after transient ischemic attack and stroke. METHODS Patients with transient ischemic attack or stroke prospectively recruited (2002-2007) into the Oxford Vascular (OXVASC) study had baseline clinical/cognitive assessment and follow-up to 2014. Dementia was diagnosed through face-to-face clinic interview, supplemented by home visits and telephone assessment in patients unable to attend clinic and by hand-searching of primary care records in uncontactable patients. RESULTS Of 1236 patients (mean age/SD, 75.2/12.1 years; 582 men), 527 (43%) died by 5-year follow-up. Follow-up assessment rates (study clinic, home visit, or telephone) of survivors were 947 in 1026 (92%), 857 in 958 (89%), 792 in 915 (87%), and 567 in 673 (84%) at 1, 6, 12 months and 5 years. Dementia developed in 260 patients, of whom 110 (42%; n=50 primary care records, n=49 home visit, and n=11 telephone follow-up) had not been available for face-to-face clinic follow-up at the time of diagnosis. The 5-year cumulative incidence of postevent dementia was 29% (26%-32%) overall but was only 17% (14% to 19%) in clinic assessed versus 45% (39%-51%) in nonclinic-assessed patients (P difference<0.001). CONCLUSIONS Exclusion of patients unavailable for clinic follow-up reduces the measured risk of postevent dementia. Use of multiple follow-up methods, including home visits, telephone assessments, and consent, to access primary care records substantially increases ascertainment of longer-term dementia outcomes.