Transient ischaemic attacks and prevention of strokes

Clinical features

These episodes are transient and therefore the diagnosis is made on the basis of the history. The onset is usually rapid over seconds or minutes. The resolution is more variable, with complete recovery in minutes to the full 24 h. A wide range of different clinical disturbances can occur. In considering them, it is important to distinguish whether they arise from the anterior circulation (the carotids) or the posterior circulation (the vertebral and basilar arteries).

Anterior circulation TIAs include:

amaurosis fugax (fleeting blindness) – loss of vision in one eye, ‘like a shutter coming down’

aphasia, or other language problems such as dyslexia or dysgraphia.

Posterior circulation TIAs include:

homonymous visual field loss

dysarthria

combined brain stem symptoms: vertigo, diplopia, dysphagia; these are rarely TIAs if they occur in isolation

bilateral weakness or sensory loss.

Anterior or posterior circulation TIAs include:

unilateral weakness affecting the face, arm or leg in isolation or combination

unilateral sensory loss affecting the face, arm or leg in isolation or combination.

TIAs rarely lead to blackouts or alteration of consciousness. If this occurs, alternative diagnoses should be considered.

Because TIAs are transient and alarming, it is often difficult for the patient to characterize them exactly. It is therefore common not to be certain whether visual loss was monocular, indicating amaurosis fugax, or hemianopic, indicating a posterior circulation TIA. If in any doubt, the investigations should be directed as for an anterior circulation event.

A history of risk factors for atheroma is important (see Table 1, p. 64). In young women, the type of oral contraceptive is important: the combined oestrogen–progestogen pill increases their risk by two to three times, but there is no increased risk with progesterone only.

Examination of a patient following a TIA usually reveals no neurological abnormalities. Occasionally a cholesterol embolus is seen on fundoscopy (Fig. 1). The cardiovascular system is more likely to reveal relevant abnormalities such as hypertension, hypertensive retinal changes, arrhythmias, heart murmur, signs of cardiac failure suggesting left ventricular dysfunction, loss of peripheral pulses and bruits.

Fig. 1 Cholesterol embolus on fundoscopy

(courtesy Peter Scanlon).

Differential diagnosis

Most TIAs are sufficiently clear-cut for a confident clinical diagnosis to be made. The conditions that produce similar presentations include the following:

Migraine: there is usually a slower progression of the neurological deficit, taking 15–30 min to develop; there are usually positive symptoms such as flashing lights or marked tingling associated with this. There is usually an associated migrainous headache.

Partial seizures: these are usually much shorter lived, lasting seconds to a few minutes; when they recur they are very stereotyped.

Transient global amnesia: this causes profound anterograde amnesia, lasting hours, with normal physical function.

Intracranial lesions: these usually produce progressive deficits; occasionally they may produce intermittent symptoms.

Metabolic changes: hypoglycaemia can produce transient neurological deficits.

Peripheral nerve lesions: for example, carpal tunnel syndrome produces intermittent sensory loss in the hands.

Investigation

Investigation is directed at looking for risk factors for vascular disease, potential sources of embolism in either the carotid arteries or in the heart, causes of tendency to thrombosis and causes of inflammatory vascular disease (see Table 1, p. 64). The investigations need to be tailored to the patient. Younger patients will require more aggressive investigation, particularly if there are no risk factors for atheroma. In these patients, careful evaluation of the heart and screening for thrombophilia and possible vasculitic processes are needed. Screening for sickle cell disease is indicated in all patients at risk.

In patients where the differential diagnosis is thought to include an intracranial lesion or partial seizures, brain imaging with either CT or MRI is indicated. An EEG may prove helpful in the diagnosis of patients with partial seizures.

Secondary prevention of stroke and transient ischaemic attacks

The risk of stroke is highest immediately after a TIA and falls quite rapidly in the days following the TIA. There is therefore a strong case for rapid assessment and early initiation of secondary prevention strategies.

Carotid stenosis

The North American Symptomatic Carotid Endarterectomy study and the European Carotid Surgery trials are landmark studies that evaluated the usefulness of this surgical procedure in a range of degrees of carotid stenosis (Fig. 2). Both studies found a reduced risk of recurrent stroke in patients with a greater than 70% stenosis in the surgical group and especially those with stenosis greater than 80% (Fig. 3). The benefit of surgery depends on achieving a low surgical morbidity and mortality (7% or less). The risk of stroke is greater with a tighter stenosis and if the plaque is ulcerated, so the benefit is greater for these patients. An occluded carotid artery poses no further risk of embolic stroke.

Fig. 2 Angiogram showing carotid stenosis.

Fig. 3 Kaplan–Maier survival curves to show survival time free of stroke in patients with 80–99% carotid stenosis following endarterectomy (surgery) and in controls.

(By kind permission of the Lancet: European carotid surgery trialists’ collaborative group 1998. Randomised trial of endarterectomy for recently symptomatic carotid stenosis; final results of the MRC European carotid surgery trial (ECST). Lancet 351: 1379–87.)

Initial studies have found angioplasty to have similar effectiveness to endarterectomy, though further studies are ongoing. This technique has proved useful in the treatment of other peripheral and coronary artery stenoses.

Primary prevention of stroke

This revolves around the control of risk factors for atheroma in the general population, in particular the control of hypertension. Control of hypertension reduces the stroke rate by 40%, regardless of age.

There is dispute about the best management of asymptomatic carotid stenosis. Trials found that the stroke risk was about 2% per year in unoperated patients compared with 1% in the operated group, suggesting a very small benefit compared with a 2% operative risk. Put another way, 86 patients need to have the operation to prevent one stroke.

Transient ischaemic attacks and prevention of strokes

Diagnosis of TIAs depends on the history.

10% of patients have a TIA prior to having a stroke.

Management relies on understanding the pathophysiology of the TIA.

Management includes control of vascular risk factors and use of aspirin, and in selected patients, anticoagulation or carotid endarterectomy.