How not to miss transient ischaemic attack

Worst outcomes if missed

Ischaemic stroke – transient ischaemic attack (TIA) is a medical emergency associated with a high risk of early ischaemic stroke. Around 10-15%of TIA patients will suffer an ischaemic stroke within three months after TIA and the majority of these occur early – a half within 48 hours. Simple risk stratification instruments such as the ABCD2 score can identify TIA patients whose risk of early stroke is even higher. Prompt diagnosis, investigation and management are therefore required.

Epidemiology

TIAs are common – the Oxford Vascular Study showed the incidence of TIA was 0.66 per 1000 per year.¹ The incidence rate is some 10-fold higher in patients above the age of 85 years. Although reported figures vary, some studies suggest up to 40% of stroke patients report symptoms of a TIA in the days prior to stroke. It is important to note that suspected TIA is more common – one half of patients referred to TIA clinics have an alternative diagnosis so GPs encounter suspected TIA frequently.

Symptoms and signs

The definition of TIA is currently debated. The traditional definition is occurrence of acute and focal cerebral or ocular symptoms lasting less than 24 hours duration, which is thought to be due to inadequate cerebral or ocular blood supply. A more recent proposed definition is an event lasting less than one hour without cerebral infarction on MRI. In primary care this distinction is not important but reminds us that the symptoms of TIA are often brief.

The most important aspect of diagnosis in suspected TIA is a detailed history. Symptoms are likely to have resolved by the time of clinical assessment so history is key. Clinical examination may reveal associated risk factors such as atrial fibrillation and hypertension.

Common symptoms of TIA arising from the carotid artery territory are:

unilateral motor weakness
dysphasia
dysarthria
unilateral sensory disturbance
amaurosis fugax
homonymous hemianopia.

TIA arising from the vertebrobasilar circulation can be more difficult to diagnose but can present with:

ataxia
diplopia
dysarthria
motor and sensory disturbance (the distribution of which may vary but is also typically unilateral).

TIA symptoms should be of sudden onset and resolve completely.

The ABCD2 score is simple risk stratification instrument based only on clinical findings. It incorporates age (1 point given if age > 60 years), blood pressure (1 point given if blood pressure is over 140 or 90 mmHg), clinical features (1 point given for speech disturbance, 2 points given for unilateral limb weakness, up to a maximum of 2), duration of symptoms (1 point given if duration greater than 10 minutes, 2 points given if duration more than one hour) and diabetes status (1 point given for the presence of diabetes mellitus). The maximum score is 7 and a total score of 4 or more can be regarded as high risk for early ischaemic stroke.

Five key questions

Was there sudden unilateral weakness or speech disturbance?
Were there other suggestive symptoms of TIA?
Are there posterior circulation TIA symptoms such as diplopia, vertigo and ataxia? These are difficult to establish on history and are less specific for TIA than limb weakness but should be taken seriously.
What was the symptom duration / have the symptoms completely resolved?
What is the ABCD2 score?

Differential diagnoses

There are numerous conditions which mimic TIA and approximately 50% of patients referred to TIA clinics have an alternative diagnosis. Examples of these are seizure, migraine disorder, transient global amnesia and causes of pre-syncope. Symptoms such as memory loss, loss of consciousness, headache and blurred vision are associated with these TIA mimics.

Investigations and early management

A rapid specialist assessment is needed to confirm diagnosis, clarify aetiology of the TIA and to initiate treatment. In patients with suspected TIA who are at high risk of early stroke (ABCD2 score of 4 or more) guidelines suggest patients undergo such assessment within 24 hours and commence an anti-platelet drug and a statin immediately. However, the aim should be to assess all patients as quickly as possible.

Brain imaging to exclude mimic should be performed, preferably with MRI. Carotid artery imaging should be performed to identify those with a symptomatic carotid artery stenosis as urgent carotid endarterectomy is of unequivocal benefit in this setting. Cardiac investigations such as ECG and prolonged ECG monitoring should be performed in most patients to identify atrial fibrillation, and echocardiography is indicated in some. Lipid levels, urea and electrolytes and a full blood count should also be checked. Other more specialised investigations may be indicated in some patients.

Five red herrings

TIA mimics – loss of consciousness, seizure, headache, memory loss are symptoms commonly associated with mimic.
Transient weakness on wakening – this is often put down to a peripheral nerve lesion but beware in patients with cardiovascular risk factors.
Ongoing symptoms – if symptoms are still present at the time of assessment you cannot assume it is a TIA. The patient may have a stroke or an alternative diagnosis.
Younger patients – although stroke and TIA are less common in younger patients, they can occur and suggestive symptoms should not be ignored.
Loss of consciousness – this is very uncommon in TIA and usually has another cause so referral to another specialty may be more appropriate.

Dr Jesse Dawson is a consultant stroke physician at the Western Infirmary in Glasgow and clinical senior lecturer at the University of Glasgow.

References