Incidence of transient ischemic attack in Rochester, Minnesota, 1985- 1989

Background and Purpose - There is scant information available on the incidence of transient ischemic attack (TIA) in a defined population. This study defines incidence rates of first TIA and subtypes of TIA during 1985- 1989 and compares the incidence to that obtained from a 1960-1972 cohort study. Methods - Medical records of all residents of Rochester with potential diagnosis of TIA during 1985-1989 were screened to determine whether the case met the criteria for TIA. All available data were used to determine the vascular distribution of the TIA. Average annual age- and sex-adjusted incidence rates were calculated for 1985-1989, and results were compared with incidence rates determined in a Rochester-based 1960,1972 cohort study. Results - Two hundred two cases of first TIA or amaurosis fugax occurred among Rochester residents during 1985-1989. The age- and sex-adjusted incidence rate for any TIA was 68/100 000 population. Incidence of amaurosis fugax was 13/100 000; anterior circulation (cerebral) TIA, 38/100 000; and vertebrobasilar distribution TIA, 14/100 000. Rates were similar to those determined from a 1960-1972 cohort study. Conclusions - The incidence rate of TIA is 41% that of stroke incidence. TIA incidence in Rochester, Minn, is higher than has been previously reported for other sites throughout the world. Although comparison with prior time periods is difficult because of ascertainment issues, it appears that there has been no significant change in TIA incidence since the decade of the 1960s or earlier. This suggests that the most common mechanism for TIA (atherosclerosis) has not changed in prevalence, nor have risk factors leading to this mechanism.