• Stroke
• TIA
• posterior circulation
• vertebrobasilar
• prognosis
• cerebrovascular disease
• scales

The effectiveness of early interventions to prevent stroke after transient ischemic attack (TIA) has led to the need for simple screening methods to identify patients with acute stroke and TIA for intervention.1 The Face Arm Speech Test (FAST) score has been developed to assess whether a patient is likely to have an acute stroke and in particular to identify patients as potential candidates for thrombolysis.2 The ABCD2 score has been developed as a screening tool to identify patients with TIA and minor stroke who are at particularly high risk of recurrent stroke and therefore need urgent investigation and treatment.3 Both have been primarily evaluated in groups of unselected stroke and TIA patients, the majority of whom have anterior circulation stroke.

Symptoms and signs associated with posterior circulation stroke differ significantly from those associated with anterior circulation stroke. We tested whether FAST and ABCD2 are less sensitive in patients with posterior, compared with anterior, cerebrovascular events.

Two hundred and sixteen consecutive patients with posterior circulation ischaemic stroke or TIA presenting as emergencies to our stroke service were recruited as previously described.4 Clinical details including history, examination and results of investigations were collected prospectively within 12 h from hospital admission, on a standard stroke register proforma. As a control group, data for 220 consecutive patients with anterior circulation stroke or TIA collected on the same prospective stroke register proforma were analysed.

The FAST test consists of three items (facial weakness, arm weakness and speech disturbance)2 and the score was calculated from a review of the accident and emergency (A&E) assessment and the stroke assessment proforma. For any positive item, one point was given. The FAST test is considered positive when any one of the three items is positive.

We also used an adjusted score to include common posterior circulation symptoms. These were visual disturbance (diplopia or visual field defect or visual blurring), vertigo and ataxia (gait or limb ataxia or unsteadiness). The adjusted FAST score comprised the original FAST score with the addition of up to one additional point when visual disturbances, vertigo or ataxia was present.

The seven-item ABCD2 score was determined by a review of the A&E and hospital records and the stroke assessment proforma. The ABCD2 score has been shown to be highly predictive of recurrent stroke risk when the score is ≥4.3 As for the FAST score, we also developed an adjusted ABCD2 score which included visual disturbances, vertigo or ataxia. In addition, all patients were prospectively followed up for 90 days as previously described for recurrent stroke.4

Neurological signs and symptoms in the two groups of patients are reported in table 1. Posterior circulation stroke patients often presented with more than one symptom and, compared with patients with anterior circulation stroke, presented more commonly with visual symptoms (diplopia and/or visual field defect), unsteadiness/ataxia, vertigo and nausea/vomiting. Patients with anterior circulation stroke presented more frequently with focal sensory defect or weakness, agnosia (any form, including visual, sensory or extinction), dysarthria, dysphasia and dysphagia. Drowsiness was equally common in the two groups.

Statistically significant difference was tested by χ² analysis.

In patients with posterior circulation stroke, the FAST score at presentation was positive (ie, ≥1) in only 131/216 (60.6%) patients. The sensitivity of a positive FAST score increased significantly to 172/216 (79.6%, p<0.001) and 176/216 (81.5%, p<0.001) if ataxia or visual symptoms, respectively, were added to the score. It increased to 147/216 (68%) if vertigo was added but this was not significant. In patients with anterior circulation stroke there was a higher proportion of patients with positive FAST scores (198/220, 91.7%) than in those with posterior circulation stroke (p<0.0001).

In patients with posterior circulation stroke the proportion of ABCD2 scores ≥4 at presentation was significantly lower than in patients with anterior circulation stroke (157/216=72.6% vs 206/220=93.6%; p<0.0001). The proportion increased significantly to 180/216 (83.3%, p=0.007) and 174/216 (80.5%, p=0.05) if ataxia or visual symptoms, respectively, were added to the score. It increased to 166/216 (76.8%) if vertigo was added but this was not significant.

Eighteen patients (8.9%) had a recurrent vertebrobasilar event in the next 90 days of follow-up. Of these patients only 13/18 (72.2%) had an ABCD2 score ≥4 at presentation. This proportion was 72.2%, 83.3% and 83.3% if vertigo, visual symptoms or ataxia, respectively, was added to the score. Changes were not significant.

These results show that commonly used screening tools for both identification and risk stratification of stroke and TIA patients are much less sensitive for the detection of posterior circulation, compared with anterior circulation, stroke.

We have shown that the FAST test failed to diagnose 40% of posterior circulation stroke in contrast to only 10% for anterior circulation stroke. Adding additional features to the screening tool increased sensitivity. Many of the features of posterior circulation stroke are fairly non-specific, such as dizziness and vertigo, but adding visual disturbance increased sensitivity from 60% to 80%. Unlike ataxia, which is likely to be difficult for paramedics to identify reliably, detection of visual disturbance may be more feasible. This approach has already been used in the ROSIER (Recognition of Stroke in the Emergency Room) scale which has been designed for emergency room physicians.5

The ABCD2 score is being increasingly used as a screening tool, and has been advocated as such in national stroke strategies. In this prospective study, we found that using a conventional ABCD2 cut-off of ≥4 approximately 30% of patients who had recurrent posterior circulation events within the first 90 days following stroke or TIA were not identified as being high risk. This proportion could be decreased by about a third if visual signs or ataxia was added.

In conclusion, both FAST and ABCD2 scores, which have been developed as screening tools for unselected strokes, are less effective in the diagnosis, and identification, of high risk cases for posterior circulation stroke and TIA. Including additional parameters in these screening tools, particularly the presence or absence of visual disturbance, can improve the sensitivity. However, whether this improvement can be obtained without an excessive loss of specificity needs to be determined.