Discussion
This study demonstrated differences in the distribution of
stroke severity between the OXVASC study population and
the Dijon population, and the 3 previously reported studies,
attributable mainly to a major disparity in the reported incidence
of minor ischemic stroke. Despite the use of multiple
overlapping sources of case ascertainment in all 5 studies, in
strict accordance with the published core criteria for conducting
ideal stroke incidence studies,4,5 residual differences in
ascertainment procedures probably contributed to the divergent
findings (Table 1). First, some cases of minor stroke not
hospitalized and not referred to the research teams may have
been missed in the other studies, none of which had access
to primary care computer systems to systematically identify
all patients coded with a cerebrovascular diagnosis. However,
only 4% of cases of ischemic stroke with an NIHSS score ≤2
in OXVASC were identified by such searches alone. Second,
and more important, the provision of a dedicated TIA clinic
for the OXVASC study population identified the majority of
minor ischemic strokes.
It has been reported previously that ≤25% of patients initially
referred by general practitioners to TIA clinics have evidence
of neurological deficits on the neurologist’s assessment and
symptoms persisting >24 hours.1,7,8,16 Assessment in TIA clinic
also allows the identification of those with persistent discrete
symptoms without signs that are coded in the NIHSS score.
The high proportion of patients with ischemic stroke with an
NIHSS score of 0 in OXVASC (22.1% versus 4.5% in Dijon)
would be consistent with this hypothesis, although many
patients with TIA and minor stroke do also present late, after
clinical signs have resolved. Encouraging referral to a research
clinic of all patients with possible TIA or minor stroke, who
would perhaps not have been referred to conventional clinical
services, might also have an effect on ascertainment. Moreover,
the fact that the incidence of TIA was also higher in OXVASC
than in Dijon argues against the hypothesis according to which