Reliable estimation of the proportion of minor stroke due to intracerebral haemorrhage

A previous hospital clinic-based study estimated that 3.5% of minor strokes are due to primary intracerebral haemorrhage, but the confidence intervals were wide. Moreover this figure may be an underestimate in older patients, who are less likely to be referred to secondary care, and who may have higher rates of intracerebral haemorrhage. Further studies are required to validate and increase the precision of this estimate and to determine any association with age, in order to plan appropriate services for minor stroke. We determined the frequency of intracerebral haemorrhage and haemorrhagic transformation of infarction in consecutive patients presenting with minor stroke (National Institute of Health Stroke Scale <= 3) in two separate cohorts: a population-based study (Oxford Vascular Study) scanned early with computed tomography, and a hospital-based stroke clinic cohort, scanned with magnetic resonance imaging. We then pooled these data in a meta-analysis with published data from similar studies identified from a systematic literature review. In the Oxford Vascular Study, of 334 cases with minor stroke (58% men, median age 75 years), 17 had intracerebral haemorrhage (5.1%, 95% confidence interval 3.2-8.0%) and four had haemorrhagic transformation of infarction (1.2%, 0.5-3.0%). In the hospital-clinic cohort, of 280 patients with minor stroke (59% men, median age 73 years), 15 had intracerebral haemorrhage (5.4%, 3.3-8.7%) and six had haemorrhagic transformation of infarction (2.1%, 1.0-4.6%). There was no trend for an increase in the frequency of intracerebral haemorrhage with age, with the lowest frequency in patients aged >= 85 years (0-3%). We identified only one previous study with a reliable estimate of the proportion of minor stroke due to intracerebral haemorrhage, and in a pooled analysis including 842 patients, the overall frequency of intracerebral haemorrhage was 4.8% (4.5-5.0%). We have shown that the proportion of minor stroke due to intracerebral haemorrhage was very similar in a population-based cohort and a hospital clinic-based cohort using different imaging strategies, and that the frequency is independent of age. A frequency of between 4.5 and 5.0% appears to be a reliable estimate at all ages.