Acute Retinal Necrosis
Acute retinal necrosis (ARN) is an inflammatory condition that primarily affects the posterior pole. It typically features posterior uveitis, with or without anterior uveitis, and retinitis, inflammatory conditions believed to be caused by viruses within the herpes family. The principal causative viral agents have been found to be Varicella Zoster Virus (VZV) as well as Herpes Simplex Virus (HSV-1 and HSV-2) via polymerase chain reaction (PCR) testing of intraocular fluid.
In 1971, Urayama and colleagues of Tohoku University in Japan reported 6 cases of a syndrome characterized by acute necrotizing retinitis, vitritis, retinal arteritis, choroiditis, and late-onset rhegmatogenous retinal detachment. This constellation of findings was termed ARN syndrome.
ARN is believed to be caused by a viral infection. Most often the causative viral agent is either VZV or less commonly HSV. Older patients more often present with VZV or HSV-1 infections while younger patients more often present with HSV-2 infections. ARN has also been reported in case reports to be associated with cytalomegalovirus (CMV) and Epstein-Barr virus (EBV), but there is limited evidence to suggest these viruses cause ARN.
Genetics are believed to play a role in an individual’s risk for ARN with antigen expression of:
HLA-DQw7, HLA-Bw62, and HLA-DR4 in American Caucasian populations and
HLA-Aw33, HLA-B44, and HLA-DRw6 in Japanese populations.
Although ARN is most commonly seen in healthy, immunocompetent individuals, immunosuppression from corticosteroids, for example, may predispose patients. Immunocompromised patients, such as those with HIV, may develop progressive outer retinal necrosis (PORN), a more aggressive viral retinitis also caused by the Herpes family viruses.
This clinical entity is uncommon in the pediatric population. Most often it affects healthy, immunocompetent adults in their fifth to seventh decade. A clear racial or gender predilection has not been consistently demonstrated.
There appear to be two distinct disease phases:
- Acute Herpetic Phase: episcleritis or scleritis, anterior (usually granulomatous) uveitis, vitreous opacification, and inflammation of the retina, retinal arteries, and choroidal vasculature. Optic neuropathy can also occur.
- Late Cicatricial Phase: Retinal holes and tears occur at the junction of normal and atrophic retina, leading to retinal detachment in 50-75% of untreated eyes. Subsequent proliferative vitreoretinopathy with fibrosis and traction on the retina also contribute to retinal detachment.
- Acute Herpetic Phase: Viral particles in the retina and vitreous provoke an intense inflammatory response. Retinal opacification corresponds with infiltration of the retina with viral particles and mononuclear cells. Lymphocytes and plasma cells, which produce antibodies to the provocative viral agent, likewise permeate the vitreous. Additionally, characteristic inflammation of the retinal arterioles occurs, resulting in vaso-occlusion and rapid necrosis of dependent, downstream retinal tissue. Choroidal vasculature may also be beset by similar inflammatory changes. An animal model of ARN suggests that involvement in the contralateral eye occurs via retrograde axonal transport to the hypothalamus and the contralateral retina.
- Late Cicatricial Phase: Organizational changes in the vitreous are thought to be the result of previous cellular infiltration during the acute phase. Contractile membranes may form in the vitreous and on the surface of the thinned, necrotic retina. Approximately 50 - 75% of patients will develop retinal detachments in the affected eye after ARN; the majority of retinal detachments occur within 3 months of the onset of ARN.
The use of systemic or intravitreal antiviral agents reduces the duration of the active phase of ARN and may thereby potentially minimize the duration and extent of retinal necrosis. Chronic use of antivirals after resolution of the active phase of ARN in one eye has also been shown to reduce the incidence of ARN in the fellow eye.
Prevention of the late visual sequelae of acute retinal necrosis, namely that of retinal detachment, may be partially reduced through prophylactic laser photocoagulation of the retina surrounding areas of prior retinitis or atrophy.
The diagnosis of ARN, prior to the advent of PCR, was originally made based on clinical criteria and the use of electron microscopy to identify viral particles in retinal tissue of enucleated eyes.
Signs and symptoms
Patients with ARN typically present with acute onset of vision loss in one eye, which may be associated with redness, photophobia, pain, floaters, and flashes. Two-thirds of cases present with unilateral involvement. The remaining third of cases present with bilateral ARN (BARN).
Anterior segment involvement may include episcleritis, scleritis, corneal edema, keratic precipitates, and anterior chamber inflammation. Classically, posterior segment involvement includes vitreous inflammation, retinal vascular arteriolitis, and peripheral retinitis. Retinitis typically begins as multifocal areas of retinal whitening and opacification, oftentimes with scalloped edges; initially, this patchy retinitis usually appears peripherally and, with progression, becomes increasing confluent and more posterior in its location.
The American Uveitis Society established the following as diagnostic criteria:
- One or more foci of retinal necrosis with discrete borders, located in the peripheral retina
- Rapid progression in absence of antiviral therapy
- Circumferential spread
- Occlusive vasculopathy, affecting arterioles
- Prominent vitritis and/or anterior chamber inflammation
The diagnosis of ARN is usually made based upon clinical characteristics. However, it may be appropriate to analyze an aqueous or vitreous sample to test for presence of members of the herpesvirus family, especially in atypical or difficult diagnostic cases. Rarely, diagnostic vitrectomy or endoretinal biopsy may be necessary.
The following tests may be performed on aqueous or vitreous samples for further diagnostic certainty:
- Viral PCR
- Viral culture
- Use of direct or indirect immunofluorescence to identify viral antigens
- Measurement of viral antibodies
- Intraocular antibody titers with calculation of the Goldmann-Witmer coefficient
- Progressive outer retinal necrosis
- CMV retinitis
- Toxoplasma chorioretinitis
- Acute multifocal hemorrhagic retinal vasculitis
- Intraocular lymphoma or leukemia
- Bacterial/Fungal retinitis or endophthalmitis
- Behcet disease
- Sympathetic ophthalmia
- Vogt-Koyanagi-Harada syndrome
- Commotio retinae
- Central or branch retinal artery occlusion
- Ocular ischemic syndrome
- Collagen-vascular disease
Without intervention, the active phase of the disease can last between 6-12 weeks, while treatment with antivirals and/or steroids may reduce the latency to 4-6 weeks. Treatment of ARN is complex and should be individualized based on overall clinical picture and vitreoretinal findings. Prospective, randomized controlled trials have not been performed given the rarity of the disease; thus, treatment recommendations are based on case reports/series. Treatment modalities may include antiviral, anti-inflammatory, and antithrombotic therapy in cases with ischemic optic neuropathy, as well as laser photocoagulation for retinal detachment prophylaxis or surgery for retinal detachment repair.
Antiviral therapy can be administered systemically (intravenously or orally) as well as via intravitreal injection. Prior to the mid-1990’s, intravenous (IV) administration of antiviral agents (usually acyclovir) was carried out for at least the first week after diagnosis of ARN because it was believed that higher serum and intraocular concentrations of the antiviral agent could be achieved; thereafter, it was considered appropriate to transition the patient to oral antivirals (acyclovir, famciclovir, valacyclovir, or valganciclovir) for an additional 4-12 weeks. With the advent of newer antiviral agents, many physicians now advocate the use of oral antiviral agents such as famciclovir, valacyclovir or valganciclovir as initial induction agents for treatment of ARN. Renal function should be monitored while patients are on systemic antivirals. Intravitreal delivery of antiviral agents is also common practice. The use of steroids and antithrombotic therapy (i.e. Aspirin) is controversial and may be used at the treating physicians’ discretion.
Commonly used systemic antiviral agents include the following which can be tapered slowly over months following resolution of the acute herpetic phase of ARN:
- Acyclovir (15 mg/kg/day divided every 8 h IV for 7 days, followed by 800 mg five times daily orally for 3–4 months)
- Famciclovir (500 mg orally q8h)
- Valacyclovir (1000–2000 mg orally q8h for induction)
- Ganciclovir (500 mg IV q12h)
- Valganciclovir (900 mg twice daily orally for 3 weeks induction, then 450 mg twice daily po for maintenance)
Antiviral agents administered intravitreally can provide beneficial adjunctive therapy, especially if retinitis is threatening the macula or optic disc:
- Ganciclovir (200-2000 ug per 0.1 mL)
- Foscarnet (1.2-2.4 mg per 0.1 mL)
Steroids may have a beneficial therapeutic effects if initiated 24-48 hours after the start of antiviral therapy or once regression of retinal necrosis been demonstrated:
- Prednisone (0.5-2.0 mg/kg/day orally for up to 6-8 weeks)
Aspirin may minimize vascular thrombosis and propagation of further retinal ischemia and necrosis. Topical steroid drops and cycloplegics have also been shown to be beneficial, depending upon the degree of anterior segment inflammation. Topical antiviral therapy has been shown not to be efficacious in treatment of ARN.
Patients with unilateral ARN should be closely followed with dilated examination of both of their eyes. Approximately 50-75% of patients with ARN will go on to develop a retinal detachment. Reports of second eye involvement range from 3-35%, with variable involvement attributable to etiologic agent, course of therapy, and immune status.
Some retina specialists advocate the use of prophylactic laser along the posterior margin of the junction of necrotic and non-necrotic retina to prevent incidence of retinal detachment. The rates of success in preventing retinal detachment are variable, and consensus does not exist on whether laser demarcation should be employed. This may be due to the confounding fact that eyes in which laser can be successfully performed typically have optically clearer vitreous, less inflammation, and thereby less risk for developing retinal detachment.
Vitrectomy with or without use of scleral buckle, with either gas or silicone oil tamponade, is usually reserved for those cases in which traction-rhegmatogenous retinal detachment occurs.
- Retinal holes and tears
- Retinal detachment
- Proliferative vitreoretinopathy
- Vitreous hemorrhage
- Macular pucker
- Optic neuropathy
The visual outcome of eyes affected by ARN is variable and largely depends upon vision at time of presentation as well as whether or not secondary retinal detachment or ischemic optic neuropathy occurs. Development of retinal detachment depends upon the extent of retinal necrosis present at the time of diagnosis, the amount of vitritis overlying areas of retinal necrosis (with more vitritis associated with a higher risk of RD), and varying response to treatment regimens.
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