Write a short note on transient ischaemic attack.

Definition

A transient ischaemic attack (TIA) is a transient episode of neurological dysfunction caused by focal brain, spinal cord or retinal ischaemia, WITHOUT acute infarction. The modern tissue-based definition has replaced the old time-based one (symptoms under 24 hours), because up to half of patients with symptoms resolving within an hour show infarction on diffusion-weighted MRI — and such patients have had a stroke, not a TIA.

Clinically, most TIAs resolve within an hour.

WHY It Matters

A TIA is a medical emergency and a warning of impending stroke. The risk of stroke is highest in the first 48 hours to 7 days, and urgent assessment and treatment reduce that risk by around 80%. The phrase to remember is that a TIA is to the brain what unstable angina is to the heart.

Aetiology

Identical to ischaemic stroke: large artery atherosclerosis with artery-to-artery embolism (carotid bifurcation, vertebrobasilar), cardioembolism (atrial fibrillation, valvular disease, endocarditis), small vessel disease, arterial dissection, and hypercoagulable states.

Clinical Features

Symptoms are sudden in onset, focal, and maximal at onset (unlike the spreading march of migraine aura or a seizure).

• Carotid territory: unilateral weakness or sensory loss of face, arm and leg; dysphasia; and amaurosis fugax — painless transient monocular visual loss, classically described as a curtain descending over the vision, from retinal artery embolism.
• Vertebrobasilar territory: bilateral or alternating weakness, ataxia, vertigo, diplopia, dysarthria, dysphagia, and bilateral visual loss.
• Non-focal symptoms — isolated dizziness, syncope, generalised weakness, confusion or incontinence — are NOT a TIA and should prompt a different line of enquiry.

Differential diagnosis (TIA mimics): migraine with aura (gradual march over minutes, positive visual phenomena, headache), focal seizure with Todd's paresis, hypoglycaemia, syncope, vestibular disorders, functional symptoms, and structural lesions such as subdural haematoma or tumour.

Risk Stratification

The ABCD2 score has traditionally been used to estimate short-term stroke risk: Age ≥ 60, Blood pressure ≥ 140/90, Clinical features (unilateral weakness scoring highest, speech disturbance without weakness next), Duration (≥ 60 minutes highest), and Diabetes.

Current practice, however, is to treat every suspected TIA as high risk and investigate urgently, rather than to use the score to defer assessment — the score has been shown to miss patients with critical carotid stenosis and atrial fibrillation.

Investigations — Urgent, Ideally Within 24 Hours

• Brain imaging — MRI with diffusion-weighted imaging is preferred and identifies infarction (which reclassifies the event as a stroke) and mimics.
• Carotid imaging (Doppler, CT or MR angiography) urgently — because symptomatic carotid stenosis requires endarterectomy within days, and delay loses the benefit.
• ECG, and prolonged ambulatory rhythm monitoring to detect paroxysmal atrial fibrillation — the yield rises with longer monitoring.
• Echocardiography where a cardiac source is suspected.
• Bloods: glucose (exclude hypoglycaemia), CBC, ESR (giant cell arteritis in the elderly with visual symptoms), renal function, lipids, HbA1c, coagulation; and in the young, thrombophilia and antiphospholipid screen, homocysteine, and vasculitis workup.

Management

1. Immediate antithrombotic therapy

• Aspirin immediately on suspicion, once haemorrhage is excluded on imaging.
• Short-course dual antiplatelet therapy (aspirin plus clopidogrel) for high-risk TIA and minor stroke, followed by single agent long term — this reduces early recurrent stroke, and the short duration limits bleeding risk.
• Anticoagulation instead of antiplatelets for atrial fibrillation and other cardioembolic sources.

2. Urgent carotid revascularisation

Carotid endarterectomy for symptomatic high-grade stenosis, performed as soon as possible (ideally within 2 weeks, and the benefit is greatest in the first days). Carotid stenting is an alternative in selected patients.

3. Aggressive risk factor modification — started immediately, not deferred

• Blood pressure control — the most effective single long-term intervention.
• High-intensity statin regardless of baseline cholesterol.
• Diabetes control; smoking cessation; weight reduction, exercise, dietary salt and alcohol reduction.
• Treat obstructive sleep apnoea where present.

4. Advice

Driving restrictions as per regulation; education on recognising stroke symptoms (FAST — Face, Arm, Speech, Time) and calling for emergency help immediately; and adherence counselling.