59.1 Features
West Nile virus (WNV) is a zoonotic disease due to a single-stranded RNA flavivirus of the same family as Japanese encephalitis, St. Louis encephalitis, and yellow fever. WNV was first described in Uganda in 1937 and the first case in the Western Hemisphere was reported in 1999 in New York City. Demonstration of ophthalmic involvement was first reported in 2003. One study found 24% of patients with WNV had WNV retinopathy.
59.1.1 Common Symptoms
Ocular
Blurred vision, photophobia, floaters, and diplopia. Vision ranges from normal to moderate–severe impairment and often returns to near baseline. Optic neuropathy, choroidal neovascularization, and vision loss from the occlusive retinal vascular disease have been reported.
Systemic
Most are asymptomatic (i.e., 80%), while approximately 20% develop WN fever and experience high-grade fever, lymphadenopathy, headache, malaise, myalgia, nausea and vomiting, and/or gastrointestinal disorders. WN meningoencephalitis may cause altered mental status and signs of aseptic meningitis. Meningoencephalitis is associated with higher risk of WNV retinopathy. Risk of developing WNV meningoencephalitis is associated with advanced age or the presence of diabetes and mortality is 5 to 10% of patients with the neuroinvasive disease. In addition, the severity of ophthalmic manifestations has also been linked to diabetes.
59.1.2 Exam Findings
Bilateral retinopathy is more common than unilateral lesions and is typically self-limited. Diabetes is a potential risk factor for multifocal chorioretinitis and advanced age is associated with prolonged recovery. Reported ocular presentations of WNV include chorioretinitis, anterior uveitis without focal lesions, occlusive retinal vasculitis and retinal hemorrhages (which may lead to permanent field defects and vision loss), congenital chorioretinal scarring in children born to previously infected mothers, disc edema or optic atrophy (possibly due to mononuclear perivascular inflammation and subsequent occlusion of the posterior ciliary vessels), and sixth nerve palsy.
Chorioretinitis staging is as follows:
Acute stage: Deep, creamy yellow multifocal nummular chorioretinal lesions with a scattered or circumlinear distribution and an average diameter of 250 µm (range 100–1,500 µm); typically in the midperiphery and may be associated with vitritis.
Chorioretinal streaks in a circumlinear distribution have been variably described but are also seen in multifocal choroiditis and ocular histoplasmosis syndrome. Anterior segment findings may include self-limited uveitis.
Subacute stage: Pigmentation begins and a cream halo may remain.
Convalescent stage: Atrophic lesions with sharp margins (▶ Fig. 59.1, ▶ Fig. 59.2).
Fig. 59.1 (a,b) Color fundus photograph of acute West Nile chorioretinitis in the right and left eyes, demonstrating yellow chorioretinal lesions, retinal hemorrhages, and vitritis. (c,d) Following the resolution of disease activity, chorioretinal lesions are more distinct with some more pigmented and others more depigmented. Vitritis has improved.
Fig. 59.2 (a) Ultra-widefield fundus photograph of convalescent stage of West Nile retinopathy. (b) Ultra-widefield fluorescein angiography of convalescent stage of West Nile retinopathy with staining and window defects related to the chorioretinal lesions.
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