Antipsychotic parkinsonism risk
Bandolier editors Dr Andrew Moore and Professor Henry McQuay discuss a new 'must-read' paper that will help GPs decide who needs urgent referral after a TIA
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 per cent in the first year and then about 7 per cent a year thereafter, with risk of stroke, heart attack or vascular death being about 10 per cent 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 per cent.
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 system1 looks like being a real help.
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:
·Age was dichotomised at 60 years.
·Hypertension was defined as elevated blood pressure after the TIA, with cut-off points of 140mmHg systolic and/or 90mmHg diastolic.
·Motor weakness was focal, usually unilateral, weakness (loss of power) of face, arm, hand or leg.
·Speech disturbance was dysarthria (impairment of articulation) or dysphasia (difficulty in speaking or understanding language), or both.
·Duration of symptoms was characterised as less than 10 minutes, between 10 minutes and 59 minutes, or 60 minutes or more.
·Diabetes was defined as treatment with oral medication or insulin.
These characteristics were tested on a derivation data set, a scoring system established, 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.
The derivation dataset had 209 probable or definite TIAs and the validation dataset 190. Based on the derivation dataset in which diabetes was eliminated, high levels of significance were found for unilateral weakness and duration of symptoms of 60 minutes or more and so the ABCD scoring system was developed.
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. In the 80 patients with ABCD scores of 5 or 6 there were 19 strokes within seven days of the TIA (24 per cent, or 1 in 4). In patients with a score of less than 5, the seven-day risk was 0.4 per cent, or 1 in 250.
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.
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.
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
Andrew Moore is honorary professor of health sciences at University College Swansea, and editor-in-chief of Bandolier
Henry McQuay is professor of pain relief at the Oxford pain relief unit and co-editor of Bandolier
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