Features
Diffuse unilateral subacute neuroretinitis (DUSN) is a typically monocular inflammatory condition caused by various subretinal nematodes. DUSN tends to affect younger individuals and is classified into early and late stages, with characteristic findings associated with each. Early disease usually does not result in dramatic vision loss and consists of recurrent, evanescent gray-white or yellow-white clusters of fundus lesions that disappear and reappear in different locations. Later disease, which is linked to more drastic visual decline, is associated with retinal arteriolar narrowing, optic disc atrophy, and degeneration of the retinal pigment epithelium (RPE).
In the United States, the disease burden is highest in the southeast, as well as the northern and Midwestern portions. In the southeast, the majority of cases are linked to a smaller nematode, whereas the larger nematode is usually identified in cases occurring in the northern and Midwestern United States.
The exact pathogenesis of the disease is unknown. The current assumption is that the ocular pathology results from a noxious reaction of the retina and optic nerve to the subretinal organism. In particular, a smaller nematode, Ancylostoma caninum (400–1,000 µm in length), and a larger nematode, Baylisascaris procyonis (1,500–2,000 µm in length), are hypothesized to lead to the disease and are thought to survive in the eye for multiple years. A. caninum is also associated with cutaneous larva migrans, which has preceded DUSN in a subset of patients. B. procyonis is a parasite found in raccoons and squirrels that causes central nervous system disease. In addition, there have been reports of neural larva migrans in association with DUSN, and serological studies have confirmed the presence of this organism in some patients. Exposure through animal contact is thought to be the mechanism of infection.
63.1.1 Common Symptoms
In early stages, patients may be asymptomatic or experience mild visual decline, scotomas, or floaters. In later stages, the visual decline is greater, including possible worsening of scotomas and floaters.
63.1.2 Exam Findings
In early disease, exam findings mainly consist of rotating crops of gray–white or yellow–white retinal lesions parallel to the path of the nematode. These lesions typically last up to 2 weeks before disappearing and can lead to scarring in late disease stages. Patients may present with optic nerve damage, resulting in an afferent pupillary defect and optic nerve swelling, vitritis, and retinal arteriolar narrowing (▶ Fig. 63.1). Less commonly reported findings include exudative changes, choroidal neovascular membranes, and intra- and subretinal hemorrhage. Rarely, a macular star may develop.
Fig. 63.1 (a) Fundus photograph of diffuse unilateral subacute neuroretinitis, demonstrating vessel attenuation and optic nerve pallor. (b) Retinal periphery demonstrates extensive pigmentary changes and vessel attenuation. Possible nematode is noted in the inferonasal area.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
