What is Frosted Branch Angiitis?
Frosted branch angiitis (FBA) is a rare and aggressive form of retinal vasculitis characterized by acute, diffuse, translucent perivascular sheathing affecting both retinal arterioles and venules, creating a distinctive appearance resembling frost-covered tree branches in winter. 1
Clinical Presentation
FBA typically presents with:
- Sudden, painless vision loss with floaters and photopsias
- Bilateral involvement in 55% of cases (lower than previously thought) 1
- Acute panuveitis with variable degrees of retinal edema 2
- Affects predominantly young, otherwise healthy patients, though age range spans from 11 months to mid-40s 3
The hallmark fundoscopic finding is widespread translucent perivascular sheathing that affects both arteries and veins, with venules more commonly involved. This may be accompanied by retinal hemorrhages, vitreous haze, and optic disc swelling 4, 5.
Etiology and Classification
FBA is classified into three categories:
- Idiopathic FBA (45.4% of cases) - No identifiable underlying cause 1
- Secondary FBA (54.6% of cases) - Associated with underlying conditions 1
- Masquerade syndrome - Mimicking other conditions
Secondary Causes Include:
- Infectious etiologies: Streptococcal infection 4, COVID-19 5, cytomegalovirus (particularly in HIV/AIDS) 6, typhoid fever 3
- Malignancies: Hodgkin lymphoma (can be initial presentation or relapse sign) 7
- Autoimmune diseases
- Immune recovery responses in immunocompromised patients 6
Distinguishing Features
Idiopathic vs. Secondary FBA:
- Idiopathic cases tend to be bilateral more frequently, diagnosed at younger ages, with more generalized fundus involvement and more translucent exudates
- Secondary FBA shows less extensive retinal hemorrhage in idiopathic forms
- However, no pathognomonic fundus features definitively distinguish the two types 1
Diagnostic Workup
A systematic evaluation is mandatory to exclude secondary causes:
- Complete blood count, inflammatory markers
- Serological testing for infectious agents (anti-streptolysin O titers, viral panels including COVID-19, CMV)
- HIV testing in appropriate clinical contexts
- Consideration of malignancy screening, particularly lymphoma
- Fluorescein angiography: Shows late vessel staining without blood flow obstruction
- Optical coherence tomography: Demonstrates inner retinal hyperreflectivity (ischemia), macular edema, subretinal fluid 4, 5
Complications and Prognosis
Critical complications to monitor:
- Retinal vein occlusion (RVO) - FBA may be a risk factor due to severe vasculitis activating coagulation cascades and causing retinal thrombosis 2
- Cystoid macular edema - Can develop weeks after initial presentation 2
- Capillary non-perfusion and retinal ischemia 4
- Neovascularization requiring panretinal photocoagulation 5
Recurrence and surgical intervention are rare 1, but close monitoring is essential given the potential for delayed complications like RVO developing several weeks after initial improvement 2.
Treatment Approach
Immediate high-dose systemic corticosteroids form the cornerstone of therapy:
- Intravenous methylprednisolone (500 mg daily for 3 days) followed by oral taper 4
- Combined with antimicrobial therapy when infectious etiology identified 4
- Anti-VEGF therapy (intravitreal bevacizumab) for secondary macular edema or RVO 2, 5
- Immunosuppression (azathioprine) for refractory cases 5
- Panretinal photocoagulation if neovascularization develops 5
Rapid response to treatment is typical, with visual recovery often occurring within days to weeks when treated promptly 4. However, delayed complications like RVO may require prolonged anti-VEGF therapy over 14-44 months 2.
Clinical Pitfall
The question of prophylactic antiplatelet therapy remains unresolved - given FBA's association with subsequent RVO development, consideration should be given to anticoagulation, though evidence is insufficient to make a definitive recommendation 2.