Transient Ischaemic Attacks

Learning objectives

Introduction

Transient ischaemic attacks are potential harbingers for developing a possibly disabling or lethal stroke. Their occurrence should be considered as a medical emergency and a warning sign that patients need rapid and expert assessment with the diagnosis confirmed or refuted, risk factors identified and treatments initiated that can significantly reduce the likelihood of future stroke. The expert opinion is firstly to confirm the diagnosis which is often the most difficult part. If the symptoms are not coming from a TIA then the stroke risks obviously do not apply. In the last 5-10 years much work has been done to both identify those at risk of stroke and setting up effective clinical pathways to see, assess and manage patients quickly.

Definition

The definition of TIA is identical to stroke except that either symptoms which may be brain or ocular last less than 24 hours or that imaging shows no evidence of brain infarction. All of the symptomatic episode must be explicable by the expected neurology caused by the transient occlusion of a cerebral vessel. If you cannot say precisely which artery and which part of the brain are involved then you need to reflect and reconsider the diagnosis. Without some diagnostic rigour it is easy to over diagnose TIA which can have serious implications for patients. All of those who see patients with TIA need to be well versed in the differentials and particularly in all the different clinical manifestations of migrainous symptomatology.

The clinical symptoms associated with TIA are pretty much identical to stroke except for the transient nature. However transient neurology over minutes or hours has a very different differential diagnosis to that of more persisting neurology and stroke. The table below shows a list of very common TIA mimics. The diagnosis of TIA is beset by the fact that there is no blood or imaging tests for it - in fact it is the lack of imaging changes that aids one in diagnosing it so there is always a degree of subjectivity in the more grey cases. The TIA clinic is one of the places where history which is 90% of the diagnosis in neurology becomes almost 99% of the diagnosis for diagnosing TIA. Great care and attention must be taken to extract exactly what happened, in what setting and get as much history from witnesses. Diagnosis must be based on the history plus a priori risk factors.

The examination (neurology will be resolved) will be looking for persisting risks e.g. hypertension, AF will help, and this will be assessed together with the presumed a priori risk of TIA in this patient. An identical presentation in an 80-year-old hypertensive diagnosed as TIA may be diagnosed as non-TIA or even unknown in an 18 year old. It is often better to say cause unknown than to assign a wrong diagnostic label. TIA should never be a diagnosis simply because there is no other explanation.

Establishing the diagnosis

Role of GP and Emergency Department: If there is any residual neurology then treat as stroke and 999 patient to the Emergency Department. If seen by GP or ED and all neurology has definitely resolved then start Aspirin 300 mg od advise patient not to drive and do immediate referral via fax or phone to local TIA clinic

Differential diagnosis

Much of the time the patients seen in the TIA clinic do not have TIAs. Many have had symptoms greater than 24 hours and made recovery and really have the diagnostic label of stroke. Others have syncope etc. Much depends on whether you screen referrals, the information given to the referrer on the form. We make our form as simple as possible and include an ABCD2 score but if the history on the form is clearly not TIA we decline the referral. If we have any doubt we see the patient.

Risk Assessment - ABCD2 scoring

A substantial risk of stroke exists in the early period after TIA. Scores have been developed to quantify risks [1].The magnitude of risk is greater and the time to event shorter than previously recognised. A recent systematic review reported an overall 7 day stroke risk of 5.2% after TIA. The most commonly used (and best validated) tool is the ABCD2 score (table 1). The ABCD2 algorithm [1] predicts a patient's very early risk of stroke following a TIA. The score is calculated according to 5 important clinical features: Age, BP, clinical features, Duration and whether the patient is Diabetic. As can be seen an age > 60 is significant. A BP > 140/90 mmHg is significant. Unilateral weakness scores higher than isolated speech disturbance. Symptoms greater than 1 hour scores highly and under 10 mins gets no score at all.

The corresponding 2 day risks for a subsequent stroke are:

ABCD2 estimates risk of recurrence at two days from 1% for patients with “low risk” to 8.1% for those patients with “high risk”. ABCD2 scoring is recommended in UK national guidelines and many centres offer same day assessment of patients at highest risk of stroke. ABCD2 may also be useful in diagnosis. Single centre registry data (3646 patients) showed that few referrals with an ABCD2 score of 0 were subsequently found to have a cerebrovascular diagnosis. Among patients diagnosed by emergency department physicians with TIA, higher ABCD2 score was associated with a greater likelihood that the diagnosis was confirmed on expert review [2].

Traditionally those with an ABCD2 score of 4 or more were considered high risk and current metrics insist should be seen=, assessed and imaged within 24 hours of initial presentation. The remainder should have the same within 7 days. The new guidance from Royal College Physicians suggests that all should be seen within 24 hours with no differentiation. It may be appropriate to perform some form of telephone triage to help separate TIA from all the other non-TIA referrals.

Investigations

• Initial Evaluation: Prompt initial evaluation same day if possible or next morning. Rapid assessment, initiation of treatment and investigation will avoid hospital admission.
• Hospitalisation: Should only be considered in those with high risk and recurring symptoms with poor access to urgent help. Strict instructions to 999 if symptoms persist for more than a few minutes. Need blue lighted by ambulance to centre that provides 24/7 thrombolysis
• Lab testing: Full blood count, ESR (especially when ocular symptoms) serum electrolytes and creatinine; fasting blood glucose and lipids
• Electrocardiography: same day. Is there AF is the main question, also recent MI, LVH, LBBB
• 24 hr Holter or 7 day Holter should be considered where PAF is being considered
• Brain imaging study: CT or MRI is preferable. One of these should be done urgently same day. MRI if needed should preferably be within 7 days to catch any DWI changes
• Vascular imaging: Carotid ultrasound should be done and is standard for looking for surgical amenable and symptomatic carotid disease. This may be backed up by CT or MR angiography

Role of the TIA clinic

Referrals

Referrals often are appropriate but sometimes are not thought through. Syncope or neurology after syncope is unlikely to be TIA and the syncope is the matter that needs addressed. Transient neurology in those with brain tumours or other intracranial pathology is unlikely TIA and likely to be the pre-existing pathology. Isolated transient dysarthria is often so non localising and non-specific that it is not helpful unless it occurs with no confounding factors, isolated vertigo is the same. Transient neurology in older patients with dementia may simply be step wise progression of dementia and these patients are unlikely to benefit from clinic visit and should be discussed with the clinical staff. Those in Nursing homes who are frail with a poor prognosis are possibly going to have little to gain by attending. The issue is also that in many cases there are equally valid alternative explanations for transient neurology. Common sense should be considered and discussion with patient and family is appropriate to determine what is in their best interest. I often phone triage and speak with all involved and if unsure can bring them to clinic.

Medical Management

• Atherothrombotic TIA: Daily long-term antiplatelet therapy: combination extended release dipyridamole plus aspirin (reasonable as first choice), clopidogrel, or aspirin alone. Anticoagulation is not recommended. Clopidogrel is preferred as price has fallen dramatically and much better tolerated and probably better compliance than with twice daily dipyridamole which often causes headache.
• Cardioembolic TIA: Long-term anticoagulation for atrial fibrillation (continuous or paroxysmal). If patient intolerant to anticoagulation, aspirin 75-325 mg daily or clopidogrel 75 mg daily if intolerant to aspirin.
• Hypertension: Lower blood pressure to < 140/90 mm Hg or < 130/80 mm Hg for diabetics, with an ACE inhibitor alone or in combination with a diuretic, or with an angiotensin-receptor blocker
• Lipids: Initiate a daily statin. Goal LDL-cholesterol level < 2.59 mmol/l (< 100mg/dl)
• Smoking: Initiate a cessation program
• Diabetes: Fasting blood glucose goal <126mg/dl
• Physical activity: Recommend =10 min of exercise such as walking, bicycling, running, or swimming =3 times/week
• Discuss driving and employment and mood, fatigue and other relevant and active problems

Surgical Assessment

• Carotid endarterectomy: Preferably within 2 weeks of cerebral or retinal TIA in those with TIA attributed to a high-grade internal carotid artery stenosis.
• 100% occluded: no surgery.
• 70-99% internal carotid artery stenosis: Recommended
• 50-69% stenosis: Recommended at centres with perioperative complication rate < 6%
• < 50% stenosis: Not recommended

References

• [1] Johnston SC1, Rothwell PM, Nguyen-Huynh MN, Giles MF, Elkins JS, Bernstein AL, Sidney S.. Validation and refinement of scores to predict very early stroke risk after transient ischaemic attack. Lancet. 2007 Jan 27;369(9558):283-92.
• [2] Josephson SA1, Sidney S, Pham TN, Bernstein AL, Johnston SC.Higher ABCD2 score predicts patients most likely to have true transient ischemic attack.Stroke. 2008 Nov;39(11):3096-8. doi: 10.1161/STROKEAHA.108.514562. Epub 2008 Aug 7.