How do I differentiate between retinal arteritis and retinal phlebitis?

Distinguishing Retinal Arteritis from Retinal Phlebitis

Retinal arteritis and phlebitis can be reliably differentiated by their distinct fundoscopic and fluorescein angiography findings, with arteritis showing arterial sheathing, delayed arterial filling, and arterial occlusion, while phlebitis demonstrates venous sheathing, perivenular hemorrhages, and irregular venous caliber.

Key Clinical Distinctions

Retinal Arteritis Features

Arteritis presents with specific arterial-focused pathology that is readily identifiable on examination:

• Arterial sheathing and segmental discontinuity of small and large retinal arteries are hallmark findings 1
• Delayed retinal arterial filling on fluorescein angiography is a critical diagnostic feature 1
• Cotton-wool spots and Kyrieleis plaques (white deposits on vessel walls) indicate arterial inflammation 1
• Sclerotic arteries with focal or elongated segmental changes 1
• Retinal vascular nonperfusion in arterial distribution territories 1
• Boxcar segmentation (slow, segmented blood flow) in retinal arterioles 2

Retinal Phlebitis Features

Phlebitis demonstrates venous-specific inflammatory changes:

• Perivenular hemorrhages and irregular venous caliber with dilated and sclerotic segments 1
• Focal venous sheathing at the site of inflammation, often not at arteriovenous crossings 3
• Vein sheathing visible on fluorescein angiography 4
• Surrounding exudation at the site of focal venular abnormality 3
• Progression to branch retinal vein occlusion at the inflammation site 3

Fluorescein Angiography Distinctions

FA is essential for definitive differentiation and reveals vessel-specific pathology:

• Arteritis shows: Delayed arterial filling, arterial nonperfusion, and variable dye leakage from affected arteries 1
• Phlebitis shows: Venous leakage, venous staining, and venous occlusive patterns 4
• Inflammatory artery sheathing (33.7% in infectious cases) versus vein sheathing patterns help distinguish the two 4

Critical Etiologic Considerations

When Arteritis Predominates

Arteritis strongly suggests specific urgent etiologies requiring immediate action:

• Giant Cell Arteritis (GCA) is the most common non-embolic cause in patients over 50 years, requiring immediate high-dose corticosteroids 5, 6
• Infectious uveitis shows significantly higher arteritis rates (57.9%) compared to non-infectious causes (11.2%) 4
• Embolic disease from carotid stenosis or cardiac sources presents with arterial occlusion patterns 2, 5

When Phlebitis Predominates

Phlebitis suggests different pathophysiologic processes:

• Focal retinal phlebitis represents a distinct entity starting with focal venular wall abnormality 3
• Systemic inflammatory diseases (SLE, sarcoidosis, Behçet's disease) can cause phlebitis 7, 4
• Non-infectious uveitis more commonly presents with venous rather than arterial involvement 4

Practical Diagnostic Algorithm

Follow this systematic approach for differentiation:

1. Perform dilated fundoscopy looking specifically for arterial versus venous sheathing patterns 5
2. Obtain fluorescein angiography to document arterial filling times, vascular leakage patterns, and areas of nonperfusion 5, 1
3. Use OCT to identify paracentral acute middle maculopathy (PAMM) suggesting arterial ischemia 5
4. Check for emboli visible in arterioles (suggests arterial embolic disease) 5
5. Assess for cotton-wool spots (more common in arteritis) versus hemorrhages (more common in phlebitis) 1, 4

Critical Pitfalls to Avoid

Arteritis is far more urgent than phlebitis due to stroke risk and GCA:

• Never delay GCA workup in patients over 50 with arteritis—check ESR, CRP immediately and start corticosteroids if clinical suspicion is high 5, 8
• Arteritis requires immediate stroke center referral within 24 hours as it represents a stroke equivalent with 3-6% stroke risk in the first 1-4 weeks 2, 6
• Infectious arteritis (57.9% of infectious uveitis) requires different treatment than non-infectious phlebitis 4
• Vitreous cells may obscure retinal details in arteritis cases, requiring high index of suspicion 1

Most Discriminating Finding

The single most reliable distinguishing feature is inflammatory artery sheathing (33.7% in infectious cases) versus vein sheathing, which is definitively visualized on fluorescein angiography showing arterial versus venous leakage patterns 4. This distinction is critical because arteritis demands urgent systemic evaluation for GCA, stroke risk, and infectious causes, while phlebitis typically indicates less immediately life-threatening conditions 5, 6, 4.