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Transient Ischaemic Attacks: Mimics and Chameleons
Chameleons
Limb-shaking TIAs
Rhythmic, involuntary jerky limb movements can occur in haemodynamic TIAs, which may thus be mistaken for focal motor seizures. The presence of limb shaking is a well-established sign of hemisphere hypoperfusion, due to severe carotid or middle cerebral artery disease. The episodes tend to be brief (<5 min), recurrent and avoid the face. They can be precipitated by activities that may reduce cerebral blood flow (such as postural change, coughing and exercise). Previously reported cases do not exhibit the Jacksonian march typical of focal motor seizures, the other main differential for this presentation. MRI, including DWI sequences, can help in showing a classical 'borderzone' pattern of established or recent ischaemia, especially if symptoms are prolonged or recurrent (figure 4).
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Figure 4.
Imaging from a patient who presented with recurrent attacks of rhythmic jerking of the left arm, related to changing from a sitting to standing position. (A) MR angiogram showing critical right middle cerebral artery stenosis. (B) Fluid-attenuated inversion recovery (FLAIR) MRI showing high signals in the right hemisphere white matter in a 'borderzone' distribution.
TIAs with Altered Conscious Level or Other Brainstem Symptoms
Loss of consciousness is not characteristic of a TIA. However, transient ischaemia of the thalami or brainstem can very rarely cause such symptoms. We have very occasionally seen patients who give a classical history of transient quadriparesis with intact cognition suggesting a 'locked-in' TIA due to brainstem ischaemia.
Spontaneous Limb Movements or Posturing Due to Brainstem Ischaemia
Occasionally, rhythmic movements of the limbs can accompany acute brainstem ischaemia. These movements may be seizure-like rhythmic jerking, sometimes with prolonged tonic muscle contractions. The movements may be intermittent, and easily confused with a seizure. It is vitally important clinically to recognise the possibility of brainstem ischaemia in such cases, as they may be a warning of impending brainstem infarction from basilar thrombosis. The pathophysiology of these movements is not well understood: they may represent a 'release phenomenon' resembling 'decerebrate' posturing, or disturbance of function of the reticular formation.
Capsular Warning Syndrome
The capsular warning syndrome is one of the most dramatic presentations in stroke medicine. In this striking phenomenon, in situ disease of a single penetrating artery is thought to cause fluctuating ischaemia and neuronal dysfunction limited to the internal capsule. The early stroke risk is high. Many attacks can occur in a short period of time (eg, 24–48 h) leading to suspicions of seizures or functional disorder in some patients. A similar phenomenon relating to pontine perforating artery ischaemia ("pontine warning syndrome") is also described.
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