Diffuse Unilateral Subacute Neuroretinitis
Diffuse unilateral subacute neuroretinitis is an uncommon but important disease likely caused by nematode infection. It should be considered in the differential diagnosis of posterior uveitis occurring among otherwise healthy, young patients (mean age, 14 years; range, 11–65 years) because early recognition and prompt treatment may preserve vision. Evidence to date suggests that DUSN is caused by solitary nematodes of 2 different sizes, apparently related to geographic region, that migrate through the subretinal space. The smaller worm, measuring 400–1000 μm in length, has been proposed to be either Ancylostoma caninum (the dog hookworm) or Toxocara canis, though the latter has never been reported to be isolated from an eye with DUSN. The larger worm is believed to be Baylisascaris procyonis (the raccoon roundworm), which measures 1500–2000 μm in length and has been found in the northern midwestern United States and Canada. The disease has also been reported outside North America.
The clinical course of DUSN is characterized by the insidious onset of unilateral loss of vision from recurrent episodes of focal, multifocal, or diffuse inflammation of the retina, RPE, and optic nerve. The early stages of the disease are marked by moderate to severe vitritis; optic disc swelling; and multiple, focal, gray-white lesions in the postequatorial fundus that vary in size from 1200 μm to 1500 μm (Fig 11-40). These lesions are transient and may be associated with overlying exudative retinal detachment. The worms may be visualized in the subretinal space, especially in the early stages. Differential diagnosis at this phase of the disease includes sarcoidosis-associated uveitis, MCP, acute posterior multifocal placoid pigment epitheliopathy, multiple evanescent white dot syndrome, serpiginous choroidopathy, Behçet disease, toxocariasis, OHS, nonspecific optic neuritis, and papillitis. The later disease stages are typified by retinal arteriolar narrowing, optic atrophy, diffuse pigment epithelial degeneration, and abnormal electroretinographic results (Fig 11-41). These findings may be confused with posttraumatic chorioretinopathy, occlusive vascular disease, toxic retinopathy, and retinitis pigmentosa. Although highly unusual, bilateral cases have been reported, as have cases of DUSN associated with neurologic disease (neural larvae migrans).
The diagnosis is made according to the aforementioned clinical picture and is most strongly supported by the observation of a worm in the subretinal space (Video 11-1). Results of systemic and laboratory evaluations are typically negative for patients with DUSN. Electroretinographic abnormalities may be present even when the test is performed early in the disease course.
Figure 11-40 Fundus photograph of diffuse unilateral subacute neuroretinitis. Note the multiple white retinal lesions and the nematode in the subretinal space (arrow).
(Courtesy of E. Mitchel Opremcak, MD.)
Figure 11-41 Fundus photographs of a 23-year-old male with diffuse unilateral subacute neuroretinitis.
(Courtesy of Howard Schatz, MD, and the Retina Image Bank, American Society of Retina Specialists.)
How to find a live worm in diffuse unilateral subacute neuroretinitis.
Courtesy of Carlos A. A. Garcia, MD.
Access the video at www.aao.org/bcscvideo_section09.
Medical therapy alone with corticosteroids may only transiently control inflammation. Direct laser photocoagulation of the worm in the early phases of the disease does not appear inflammatory and may be highly effective in halting progression of the disease (see Fig 11-38). Successful treatment and immobilization of the subretinal worm have been reported with oral thiabendazole (22 mg/kg twice daily for 2–4 days with a maximum dose of 3 g) and albendazole (200 mg twice daily for 30 days), which may be a better-tolerated alternative. Thus, if the worm cannot be visualized, patients may undergo a course of antihelminthic therapy to increase the chance of identifying and treating the nematode. In patients who undergo laser and inflammation does not improve, antihelminthic therapy may treat a presumed second unvisualized nematode.
Cortez R, Denny JP, Muci-Mendoza R, Ramirez G, Fuenmayor D, Jaffe GJ. Diffuse unilateral subacute neuroretinitis in Venezuela. Ophthalmology. 2005;112(12):2110–2114.
de Amorim Garcia Filho CA, Bezerra Gomes AH, de A Garcia Soares AC, de Amorim Garcia CA. Clinical features of 121 patients with diffuse unilateral subacute neuroretinitis. Am J Ophthalmol. 2012;153(4):743–749.
Souza EC, Casella AM, Nakashima Y, Monteiro ML. Clinical features and outcomes of patients with diffuse unilateral subacute neuroretinitis treated with oral albendazole. Am J Ophthalmol. 2005;140(3):437–445. [Erratum appears in Am J Ophthalmol. 2006;141(4):795–796.]
Excerpted from BCSC 2020-2021 series: Section 9 - Uveitis and Ocular Inflammation. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.