Transient Ischaemic Attack – Obtaining a Differential Diagnosis and Predicting Patient Risk
More recently, the distinction between TIA and its mimics has been studied and tools have been proposed.9,10
Such tools are developed
by studying a cohort of patients with suspected TIA, of whom some have an eventual TIA diagnosis and others have a mimic diagnosis; predictive features of each diagnosis are identified and combined in a scoring system. The drawback of such an approach is that TIA is a heterogeneous condition with a wide range of possible presentations so that only a very complex tool would have the necessary sensitivity, at the expense of its specificity. They therefore do not present an alternative to expert assessment, but may be useful in primary or emergency care for use by the non-specialist. In general, a diagnosis of TIA is supported by a sudden onset of definite, focal symptoms attributable to a specific vascular territory, while a diagnosis of a mimic is supported by other features, such as non-sudden onset, seizure activity, pre-syncope or syncope.
Some conditions are particularly frequently misdiagnosed as TIA (see Table 1), but features in the history are often helpful in distinguishing TIA from mimics (see Table 2).
Migraine with Aura
Typical migraine presenting with aura and headache, with or without nausea or vomiting, does not present a diagnostic challenge. However, sometimes a migraine aura can develop in an individual without previous migraine and without subsequent headache. In this situation, the slow intensification and then fading of symptoms over time, often with gradual spread from one domain to another (for instance vision to speech), is suggestive of migraine as opposed to TIA.11
Epilepsy
Partial seizures and post-ictal paralysis are often mistaken for TIA. Todd’s paresis is a focal neurological deficit that can follow up to 10% of seizures, most commonly grand mal seizures, and typically causes a unilateral motor weakness but can also cause diplopia or speech disturbance. The cause of Todd’s paresis is unknown, but ‘exhaustion’ of the primary motor cortex or inactivation of motor fibres by N-methyl-D-aspartate (NMDA) receptors have been postulated. Like a TIA, Todd’s paresis can last for several hours and differentiation depends mainly on establishing the presence of seizure activity at onset.12
Partial sensory seizures tend to cause
positive symptoms such as tingling, and symptoms ‘march’ across a hand or foot and up the limb in around a minute, and may eventually be accompanied by focal motor seizures or secondary generalisation.
Intracranial Structural Lesions
Occasionally, but importantly, intracranial structural lesions such as subdural haematoma or tumour may cause transient neurological deficit, although the mechanism is unclear. Compression of an intracranial artery, sudden expansion caused by in situ haemorrhage or oedema, or focal seizures are all possible mechanisms for transient symptoms in otherwise ‘chronic’ conditions. Additional features in the history such as headache or nausea, systemic symptoms and stuttering or gradual onset are suggestive of non-TIA diagnoses. Imaging with non-contrast computed tomography (CT) lacks sensitivity for space-occupying lesions, and MRI is superior.
Transient Global Amnesia
Transient global amnesia (TGA) presents with a characteristic syndrome of sudden-onset, severe, anterograde amnesia, often accompanied by retrograde amnesia. Attacks last several hours,
EUROPEAN NEUROLOGICAL REVIEW
Table 1: Causes of Transient Focal Neurological Symptoms
Transient ischaemic attack Migraine with aura Partial epileptic seizures Structural intracranial lesions: Tumour Chronic subdural haematoma Vascular malformation Giant aneurysm Multiple sclerosis
Labyrinthine disorders: Meniere’s disease or benign positional vertigo Peripheral nerve or root lesion Metabolic derangement: Hyperglycaemia Hypercalcaemia Hyponatraemia
Psychological Transient global amnesia
Table 2: Features of Patient History Less Typical of Transient Ischaemic Attack, with Alternative (Mimic) Diagnosis Suggested
Symptom Description Timing Onset Recurrent/
stereotypical episodes Stuttering
Progressive Ill-defined
Non-focal Positive Headache
Hearing loss/ tinnitus
Course Recall Fluctuating Absent Patchy TGA = transient global amnesia.
during which the patient appears bewildered and typically repetitively asks the same or related questions, and after which the patient makes a full recovery but has no memory of the attack.13,14
The aetiology of
TGA is unclear, but mechanisms including temporary metabolic abnormality in the medial temporal lobes, venous hypertension, focal ischaemia and seizure activity have been proposed.15
Vestibular Dysfunction
The acute onset of vertigo is common and presents a diagnostic challenge, especially in elderly patients with pre-existing risk factors for vascular disease. ‘True vertigo’, or the false illusion of movement of the patient relative to the surroundings, should be distinguished from other, less specific symptoms of ‘unsteadiness’ or ‘light-headedness’.
45
Non-neurovascular Notes Diagnosis Suggested Anxiety-related
Tumour Migraine Delirium
Symptoms Prodrome/aura Migraine Seizure Syncope Delirium
Migraine Migraine
Labyrinthine disorder
Tumour Delirium TGA
Seizure Delirium
Especially hemisensory loss
Over hours/days Over minutes
Loss of consciousness Reduced attention
Labyrinthine disorder Balance disturbance Seizure
Motor symptom Visual spectra
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