What is the most likely diagnosis for a 42-year-old woman with mild diabetes and no hypertension who had a brief, unilateral (right eye) transient loss of vision lasting a few minutes?

Diagnosis: Amaurosis Fugax (Transient Monocular Vision Loss)

This patient experienced amaurosis fugax, a transient retinal ischemic attack that requires immediate emergency evaluation as a stroke equivalent, with urgent carotid imaging and stroke risk assessment within 24 hours. 1, 2

Clinical Presentation and Mechanism

Your patient's brief unilateral vision loss lasting minutes that completely resolved is the classic presentation of amaurosis fugax (transient monocular blindness). 1 This represents temporary reduction of blood flow to the right eye, typically described as a "shade drawn upward or downward over the field of view." 1

The most common cause is atherosclerosis of the ipsilateral (right) internal carotid artery, though multiple other etiologies exist. 1 The mechanism involves ophthalmic artery embolism from fibrin, cholesterol crystals (Hollenhorst plaques), or atheroembolism. 1

Immediate Management (Within 24 Hours)

This is a medical emergency requiring immediate referral to an emergency department or stroke center within 24 hours without delay for additional testing. 2 The risk of stroke is highest within the first 7 days after the event. 2, 3

Required Urgent Workup:

• Brain MRI with diffusion-weighted imaging (DWI) to identify silent brain infarctions, which occur in 19-25% of patients with retinal artery events 2, 4

• Carotid artery imaging (duplex ultrasound, CTA, or MRA) is critical, as clinically significant carotid stenosis is discovered in up to 70% of patients with symptomatic retinal artery events 2, 4, 3

• Comprehensive cardiac workup including ECG and echocardiography to evaluate for atrial fibrillation, valvular disease, and other cardiogenic embolic sources 2

• ESR and CRP in all patients over 50 years to exclude giant cell arteritis, even without classic symptoms 4, 3

Risk Stratification for This Patient

Your patient has diabetes, placing her at intermediate stroke risk. The 3-year stroke risk with medical treatment alone in patients with transient monocular blindness is stratified by vascular risk factors (hypertension, hypercholesterolemia, diabetes, smoking): 1

• 0-1 risk factors: 1.8% stroke risk
• 2 risk factors: 12.3% stroke risk
• 3-4 risk factors: 24.2% stroke risk

With diabetes alone (assuming no other risk factors documented), she has at least 1 risk factor, but full assessment requires checking for hypertension, hypercholesterolemia, and smoking status. 1

Time-Sensitive Treatment Considerations

If High-Grade Carotid Stenosis (>70%) is Found:

Carotid endarterectomy (CEA) should be performed within 2 weeks of symptom onset for maximum benefit. 1, 2 The benefit of CEA is greatly diminished beyond 2 weeks, and after 4 weeks in women, the benefit is no more than that for asymptomatic patients. 1

Immediate Medical Therapy:

• Start antiplatelet therapy immediately without delay 2
• Aggressive control of diabetes, and screening/treatment of hypertension and hyperlipidemia 2

Differential Diagnosis to Consider

While amaurosis fugax from carotid atherosclerosis is most likely, other causes must be excluded: 1

• Carotid artery dissection (requires urgent vascular imaging)
• Cardiogenic embolism (requires cardiac evaluation)
• Giant cell arteritis (less likely at age 42, but check ESR/CRP if any headache, jaw claudication, or scalp tenderness) 4, 3
• Migraine with aura (typically has positive visual phenomena, not pure vision loss)
• Hypotension (check blood pressure)
• Glaucoma (requires ophthalmologic examination)

Critical Pitfalls to Avoid

Do not delay emergency referral to perform ophthalmologic workup first - only one-third of ophthalmologists currently transfer these patients immediately despite guideline recommendations. 2 Transfer directly to a stroke center.

Do not miss the narrow 2-week window for carotid endarterectomy if high-grade stenosis is found - surgical benefit is time-dependent and greatest within 2 weeks. 2

Do not assume vision recovery eliminates stroke risk - up to 24% of patients with retinal artery events have concurrent cerebrovascular accidents on MRI, and stroke risk remains elevated for 30 days. 2, 5

Do not confuse with transient visual obscurations (TVOs) - these last only seconds (not minutes) and represent optic nerve head ischemia from raised intracranial pressure requiring papilledema evaluation, not stroke workup. 2

Long-Term Implications

In addition to stroke risk, permanent blindness may occur in the affected eye from initial or subsequent episodes. 1 Patients with acute retinal arterial ischemia are at high risk for subsequent strokes and myocardial infarctions. 5 Secondary prevention with aggressive vascular risk factor modification is essential. 6