TRANSIENT ISCHEMIC ATTACK
DefinitionThe most common cause of short-term neurological episodes is a transient ischemic attack, or TIA. A TIA is defined as a neurological deficit lasting less than 24 hours, caused by brain ischemia. In fact, the more typical duration for a TIA is about 10 minutes; longer deficits probably produce at least some permanent brain damage.
The symptoms of a TIA depend on the artery being occluded. Carotid TIAs can present as unilateral weakness, motor or sensory disturbances of the face or upper or lower limb, dysphasia, or homonymous hemianopsia. "Amaurosis fugax" refers to transient monocular blindness due to a carotid TIA involving the territory of the ophthalmic artery. In contrast, vertebrobasilar TIAs present with bilateral or side alternating weakness, motor and sensory disturbances, as well as varying degrees of homonymous visual impairment, gait ataxia, diplopia, dysphagia, dysarthria and dizziness. It should be noted that isolated symptoms of dizziness, dysequilibrium, tinnitus, transient amnesia, and drop attacks are generally not due to TIA.
The most likely cause of a TIA is the blockage of the cerebral blood vessel by an embolus or thrombus that then subsequently dissolves, allowing blood flow to resume before permanent damage occurs (see Stroke Mechanisms). Another possibility is vasospasm leading to temporary narrowing of the blood vessel lumen.
A diagnosis of TIA is usually made after the symptoms have passed. When an ischemic neurological deficit is only a few minutes old, the likelihood that it will revert to normal within 24 hours and thus be termed a TIA is 50%. After 2 hours, the probability is only 10%.