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High-risk mini strokes

Study
Results
Comment

A transient ischaemic attack (TIA) is usually defined as causing symptoms for less than 24 hours, but it is unlikely that brain or eye is actually ischaemic for more than a few minutes. What we observe is the clinical effects of reversible impairment of neuronal function resulting from a short period of ischaemia. The risk of stroke after a TIA is about 12% in the first year and then about 7% a year thereafter, with risk of stroke, heart attack or vascular death being about 10% a year. This is about seven times the risk in the background population. But there is also a high risk of stroke in the seven days after a TIA, possibly as high as 10%.

Although patients with a suspect TIA should be assessed and investigated within a week, this is often not achieved in practice. The problem may be deciding not what sort of care is most appropriate, but which patient having a TIA needs emergency assessment? A simple diagnostic scoring system [1] looks like being a real help.

Study

The likelihood of chance associations related to TIA and subsequent seven-day stroke was eliminated by using only factors previously significantly found to be independent predictors of stroke in the three months after a TIA. These were age, clinical features characterised (motor weakness and speech disturbance), duration of symptoms, diabetes, and hypertension. The criteria decided upon were:

These characteristics were tested on a derivation data set, a scoring system established (Table 1), and the scoring system tested on a validation data set. The derivation and validation data used information from several large population-based cohort studies performed in Oxford over several years. Two main studies each had about 100,000 people, with high levels of case ascertainment, and of follow up.



Table 1: ABCD scoring system



ABCD
Meaning
Question
Score
A Age <60 years
0
    ≥60 years
1
B Blood pressure Systolic >140 mmHg and/or diastolic ≥90 mmHg
1
C Clinical features Unilateral weakness
2
Speech disturbance without weakness
1
    Other
0
D Duration of symptoms ≥60 minutes
2
10-59 minutes
1
    <10 minutes
0


Results

The derivation dataset had 209 probable or definite TIAs and the validation dataset 190. Based on the derivation dataset in which diabetes was eliminated, and high levels of significance were found for unilateral weakness and duration of symptoms of 60 minutes or more, the ABCD scoring system was developed (Table 1).

This was tested on the validation data set, where 19/20 strokes occurring in the seven days after TIA had ABCD scores of 5 or 6 (Figure 1). In the 80 patients with ABCD scores of 5 or 6 there were 19 strokes within seven days of the TIA (24%, or 1 in 4). In patients with a score of less than 5, the seven day risk was 0.4%, or 1 in 250.



Figure 1: Results of scoring





All of the strokes within seven days occurred in people with focal weakness or speech disturbance, and 16/20 had focal weakness. Focal weakness or speech disturbance, being older than 60 years, or duration of symptoms of 60 minutes or more captured 18 of 20 strokes.

Comment

This is a beautiful example of how to create and test a simple clinical scoring system. It used good quality derivation and validation data. There is much more to this study than Bandolier can capture, and, though detailed, it is one of those must-read papers. It will be useful to GPs, nurses, and emergency room staff to identify high risk of stroke after TIA, and to make appropriate decisions about how and where to care for such patients. Best of all, it provides a simple way for anyone to use some simple observations to judge the need for urgent hospital referral after a TIA.

Reference:

  1. 1 PM Rothwell et al. A simple score (ABCD) to identify individuals at high early risk of stroke after transient ischaemic attack. Lancet 2005 366: 29-36.

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