Sunday, November 13, 2011

Amaurosis Fugax and Transient Ischemic Attack

Signs and Symptoms
Both amaurosis fugax (AF) and transient ischemic attack (TIA) are diagnosed almost exclusively by history alone. Patients with both AF and TIA are typically elderly with a history of diabetes, hypertension, or generalized atherosclerosis. Younger patients with these conditions may have a history of cardiac valve disease, blood constituent or coagulation abnormalities, or drug use.

Amaurosis fugax is a painless, monocular loss of vision, which may be total or sectorial. This is a traditional blackout of the patient’s vision. Amaurosis fugax can occur in isolation, antecedent, or crescendo and is unprovoked and unpredictable. Vision loss typically lasts only seconds, but may last for hours and will resolve completely. There are no other neurological symptoms or findings in association with AF.

Transient ischemic attacks can result in a total painless loss of monocular vision; however, TIA may occur with no ocular involvement whatsoever. Other significant neurological signs and symptoms associated with TIA include dysphasia, contralateral hemiparesis, and paresthesia. Temporary paresis most commonly involves the contralateral arm, leg, or both face and arm, or both arm and leg. Numbness typically involves the contralateral hand, foot, face, and contralateral half of the tongue. A TIA will typically last for 15 minutes, but may go for hours.

TIA and AF result from either an embolic, thrombotic, vasospastic, or hematological phenomenon. Thrombus development occurs via cholesterol deposition and atheroma formation within vessel lumens. From this process forms a thrombus, which may cause transient blood flow cessation and symptoms of TIA or AF. Also, inflammatory cell infiltration of the muscular walls of arteries in giant cell arteritis will lead to lumen narrowing and occlusion with resultant TIA or AF. More commonly, however, the thrombus ulcerates and releases particles which lodge within vessels and result in distal ischemia. This produces the signs and symptoms of TIA or AF. Occasionally, cholesterol emboli is seen lodged at a retinal arteriole bifurcation in patients experiencing AF. However, visible retinal emboli are often not observed as their very nature allows for the emboli to break up and move distally. This explains why cholesterol emboli typically result in transient neurologic deficits. Calcific emboli may dislodge from the heart and indicate valve disturbance. This type of emboli is not malleable and more likely to cause a permanent occlusion of the retinal arteriole.

Vasospastic causes of TIA and AF may be due to non-embolic idiopathic arterial narrowing or the possible release of an as-yet-unidentified vasospastic substance. Occasionally, use of exogenous sources such as cocaine may lead to localized vasospasm and TIA and AF.

Hematological causes of TIA and AF result when there are abnormalities in the normal blood constituents. Hematological causes include polycythemia, sickle cell disease, anemia, and hypercoagulable states.

There is significant morbidity and mortality associated with TIA and AF. Patients experiencing uncomplicated AF have an 85 percent likelihood of full recovery while 10 to 15 percent will eventually develop a central retinal artery occlusion. The average untreated annual stroke rate of patients with untreated AF is 2 percent. Refer these patients to a neurologist or internist for carotid artery studies, such as Doppler imaging or magnetic resonance angiography. If there is significant stenosis of the carotid artery, consult a vascular surgeon for possible endarterectomy. However, these patients are typically medicatedwith blood thinners such as aspirin and they do quite well.

Patients experiencing hemispheric TIA are at more risk. The average annual untreated stroke rate in this group is 8 percent. Refer this patient to a neurologist since other neurological areas are involved in the attack. Typically, this patient requires carotid endarterectomy. The patient with hemispheric TIA has a 25 percent mortality rate within one month, 33 percent within six months, and 60 percent within seven years.

Patients who experience either TIA or AF and have retinal emboli visible at ophthalmic exam also have a high rate of mortality. In this group, the mortality rate is 15 percent within one year, 29 percent within three years, and 54 percent within seven years. In this group, cardiac death is more prevalent than stroke and thus these patients must be referred to a cardiologist.

Clinical Pearls

Amaurosis fugax in elderly patients may be the initial sign of giant cell arteritis. In these cases, devastating vision loss from anterior ischemic optic neuropathy likely ensues within several weeks of an episode of AF. These patients need an immediate Westgren ESR, and possible temporal artery biopsy, along with the requisite carotid studies.

Most cases of TIA and AF show no visible evidence at examination. These diagnoses can be made by history. Optimal management involves referral to the appropriate medical specialist.

The number one hematological cause of AF is sickle cell disease.


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